Friday, August 22, 2014

EARTHQUAKES AND FAULTS


Causes of Earthquakes
There are basically three types: 

1. VOLCANIC
2. TECTONIC
3. COLLAPSE

(Also man-made due to nuclear explosions) 



Tectonic Earthquakes 

Most earthquakes occur at plate margins due to tension, compression or shearing forces.
Rocks at plate margins are in constant motion and are being pushed, pulled, bent, twisted and folded.
Inevitably at some point they must break or crack to produce FAULTS!!
[Note – some rocks break much more easily than others]


What is a Fault?
A fault is a break or fracture between two blocks of rocks in response to stress.
Three types of stresses produce faults 1) Tension
2) Compression
3) Shear

One block has moved relative to the other block.
The surface along which the blocks move is called a fault plane.


 
There is a chicken and egg relationship between faults and earthquakes

  1. 1)  It was initially thought that earthquakes caused faulting (but then what caused the earthquake?)
  2. 2)  It was later realized that faulting produced the earthquakes.
          Thus earthquakes may occur because:-

  1. a)  Rocks are initially broken to produce a fault.
  2. b)  Movement or re-activation of an already existing fault.
 
 



















 








































Saturday, February 2, 2013

MONOHYBRID AND DIHYBRID CROSS

Monohybrid Cross 
  • is a method of determining the inheritance pattern of a trait between two single organisms.
  • a cross between parents who are true-breeding for a trait; i.e., both are homozygous for one allele of the gene, for example AA x aa, in which A is the dominant allele for a trait and a is the recessive allele for that same trait.

Sample Problem

In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds?

Analysis

  • The figure above represents a monohybrid cross of F1-hybrid plants. 
  • Both parent plants are heterozygous (Ss) for an allele that determines seed shape. 
  • Presence of the dominant allele (S) in homozygous (SS) or heterozygous (Ss) plants results in spherical seeds. 
  • Homozygous recessive (ss) plants have dented seeds.
  • To solve the sample problem, youll need to set up a Punnett square.
  • Punnett square - a diagram that is used to predict an outcome of a particular cross or breeding experiment

Steps to Solve the Sample Problem

  • Set up a 2 by 2 Punnett square.
  • Write the alleles for parent 1 on the left side of the Punnett square.
  • Each gamete will have one of the two alleles of S the parent. In this particular cross, half of the gametes will have the dominant (S) allele, s and half will have the recessive (s) allele. We will use blue and brown to keep track of the alleles of each parent.
  • Write the alleles for parent 1 on the left side of the Punnett square.
  • Each gamete will have one of the two alleles of S the parent. In this particular cross, half of the gametes will have the dominant (S) allele, s and half will have the recessive (s) allele. We will use blue and brown to keep track of the alleles of each parent.
  • Write the alleles from parent 2 above S s the Punnett square.
  • For this heterozygous parent (Ss), half of the S gametes will have the dominant (S) allele, and half will have the recessive (s) allele.
  • Fill the squares for parent 1.     S s 
  • Fill each square with the allele from Parent 1 that lines up with the row.    SS S s
  • Fill the squares for parent 2.     Ss ss
  • Fill each square with the allele from Parent 2 that lines up with the column.
  • Interpreting the results of a Punnett S s square 
  • Genotypes that resulted from this monohybrid cross  (Ss x Ss) 
                                 25% homozygous dominant
                                 50% heterozygous 
                                 25% homozygous recessive
  • Phenotypes that resulted from this monohybrid cross  (Ss x Ss) 
                                75% Spherical 
                                25% Dented

Dihybrid cross  
  • is a cross between F1 offspring (first generation offspring) of two individuals that differ in two traits of particular interest.
  • used to test for dominant and recessive genes in two separate characteristics
  • The rules of meiosis, as they apply to the dihybrid, are codified in Mendels First Law and Mendels Second Law, which are also called the Law of Segregation and the Law of Independent Assortment, respectively
Example Problem

In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and disk- shaped fruit (D) is dominant over sphere- shaped fruit (d).. If a squash plant true- breeding for white, disk-shaped fruit is crossed with a plant true-breeding for yellow, sphere-shaped fruit, what will the phenotypic and genotypic ratios be for: 

                     a. the F1 generation?
                     b. the F2 generation?

Steps to Solve the SampleProblem

  • Write down the cross in terms of the parental (P1) genotypes and phenotypes: 
              WWDD (white, disk-shaped fruit) X wwdd (yellow, sphere- shaped fruit)
  • Determine the P1 gametes, place them in a Punnett Square and fill in the resulting genotypes:   WWDD  X wwdd   

  • Determine the genotypic and phenotypic ratios for the F1 generation: 
All F1 progeny will be heterozygous for both characters (WwDd) and will have white, disk- shaped fruit .
  • Write down the cross between F1 progeny: 
                 WwDd (white, disk-shaped fruit) X WwDd (white, disk-shaped fruit)
  • Determine the F1 gametes, place them in a Punnett Square and fill in the resulting genotypes:
  • Determine the genotypic and phenotypic ratios for the F2 generation:
      Genotypic ratios:
 
1/16 will be homozygous dominant for both traits (WWDD)
 2/16 will be homozygous dominant for
color and heterozygous for shape (WWDd)
 2/16 will be heterozygous for
color and homozygous dominant for shape (WwDD)
 1/16 will be homozygous dominant for
color and homozygous recessive for shape (WWdd)
       4/16 will be heterozygous for both traits  (WwDd)
              2/16 will be heteozygous for color and homozygous recessive for shape (Wwdd)
       1/16 will be homozygous recessive for color and homozygous dominant for shape (wwDD)
  2/16 will be homozygous recessive for
color and heterozygous for shape (wwDd)      1/16 will be homozygous recessive for both traits (wwdd)
     This is a 1:2:2:1:4:2:1:2:1 genotypic ratio

  • Determine the genotypic and phenotypic ratios for the F2 generation:
     Phenotypic ratios:

9/16 will have white, disk-shaped fruit
3/16 will have white, sphere-shaped fruit
3/16 will have yellow, disk-shaped fruit
1/16 will have yellow, sphere-shaped fruit
     This is a 9:3:3:1 phenotypic ratio
















PUNNETT SQUARE

A Punnett square is a chart which shows/predicts all possible gene combinations in a cross of parents (whose genes are known). Punnett squares are named for an English geneticist, Reginald Punnett. He discovered some basic principles of genetics, including sex linkage and sex determination. He worked with the feather color traits of chickens in order to quickly separate male and female chickens. 


Genetic Problem using Punnett Squares - Example and Steps

Sample Problem

*In pea plants (which Gregor Mendel studied), tall pea plants are dominant over short pea plants. Using Punnett Squares, you can predict the genotypes and phenotypes of the offspring of a cross between a homozygous (purebred) tall pea plant and a homozygous (purebred) short pea plant. 


Step 1.
Designate letters which will represent the genes/traits. Capital letters represent dominant traits, and lowercase letters represent recessive traits. 
             T = tall t = short 
Step 2.
Write down the genotypes (genes) of each parent. These are often given to you or are possible to determine.
genotype = the genes of an organism; for one specific trait we use two letters to represent the genotype.

              TT X tt
                      (tall) (short) - both homozygous (same) or purebred 

Step 3.
List the genes that each parent can contribute.
                                                           Parent 1 Parent 2

Step 4.
Draw a Punnett square - 4 small squares in the shape of a window. Write the possible gene(s) of one parent across the top and the gene(s) of the other parent along the side of the Punnett square.




Step 5.
Fill in each box of the Punnett square by transferring the letter above and in front of each box into each appropriate box. As a general rule, the capital letter goes first and a lowercase letter follows.


Step 6.
List the possible genotypes and phenotypes of the offspring for this cross.
The letters inside the boxes indicate probable genotypes (genetic makeup) of offspring resulting from the cross of these particular parents. There are 4 boxes, and the genotypic results can be written either as fractions or percents. In this case, all 4 boxes out of the 4 are showing the Tt genotype. Therefore, each of the offspring has a 4/4 or 100% chance of showing the Tt genotype.

We have also written the phenotype (physical appearance) in each box under the genotype. Remember, T = tall and t = short (see step #1 above). Since a capital letter indicates a dominant gene, T (tall) is dominant over t (short). Therefore, each of the offspring has a 4/4 or 100% chance of being tall. 


What are the possible genotype(s) of a tall plant? 

What are the possible genotype(s) of a short plant? 

What would be the phenotype of TT? 

What would be the phenotype of tt? 

Why is the phenotype of Tt tall and not medium/average?


Practice

Using the steps of the Punnett Squares  do some Punnett squares on your own. Grab your paper and a pencil. For each problem, be sure to do the work for each step and don't forget the genotypes and phenotypes of the offspring. We'll get you started with the first problem.

Problem #1 - Use a Punnett square to predict the genotypic and phenotypic outcome (offspring) of a cross between two heterozygous/hybrid tall (Tt) pea plants. 

Step 1 - Designate letters which will represent the genes/traits. 

         T = tall t = short (and they do not always have to be the letter T!

Step 2 - Write down the genotypes of each parent. It is helpful if you write the phenotype in parenthesis under the genotypes. 

           Tt X Tt
        (tall) (tall) 


Step 3 - List the genes that each parent can contribute.

Step 4 - Write the possible gene(s) of one parent across the top and the gene(s) of the other parent along the side of the Punnett square.



*Now you're on your own to finish Steps 4 through 6.

Problem #2 - In pea plants, yellow peas are dominant over green peas.
Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between a plant heterozygous/hybrid for yellow (Yy) peas and a plant homozygous/purebred for green (yy) peas. 


Problem #3 - In pea plants, yellow peas are dominant over green peas.
Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross between two plants heterozygous for yellow peas.










Saturday, January 19, 2013

DNA TIMELINE

PRE 1920s

1866

Gregor Mendel (1822-1884), Father of Genetics

Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next. Mendel's Laws of Heredity are usually stated as:

1) The Law of Segregation: a gene pair defines each inherited trait. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.


2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.


3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.


The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of progeny number and type. Mendel's work and his Laws of Inheritance were not appreciated in his time. It wasn't until 1900, after the rediscovery of his Laws, that his experimental results were understood.


1869

FRIEDRICH MIESCHER (1844-1895)

Friedrich (Fritz) Miescher isolated the first crude preparation of DNA, he just didn't know it. He named it nuclein. Fritz came from a well-respected family that was part of the intellectual elite in Basel, Switzerland.
Miescher was an excellent student despite his shyness and a hearing handicap. Miescher initially wanted to be a priest, but his father opposed the idea and Miescher entered medical school.
He decided to base his career on medical research. He experimented and isolated a new molecule - nuclein - from the cell nucleus. Miescher continued to work on nuclein for the rest of his career.
Miescher himself believed that proteins were the molecules of heredity. However, Miescher laid the groundwork for the molecular discoveries that followed. Miescher died in 1895 from tuberculosis.

1900


CARL ERICH CORRENS (1864-1933)

 Carl Correns was born in Münich, Germany, and was orphaned at an early age. He was raised by his aunt in Switzerland. In 1885, he entered the University of Münich to study botany. Correns was a tutor at the University of Tübingen when he began to experiment with trait inheritance in plants in 1892.
Correns was active in genetic research in Germany, and was modest enough to never have a problem with scientific credit or recognition. In 1913, Correns became the first director of the newly founded Kaiser Wihelm Institut für Biologie in Berlin-Dahlem. Unfortunately, much of his work was unpublished and destroyed when Berlin was bombed in 1945.


 
HUGO DE VRIES (1848-1935)


Hugo de Vries was born in Haarlem, Netherlands. He was a Professor of Botany at the University of Amsterdam when he began his genetic experiments with plants in 1880. He completed most of his hybridization experiments without knowing about Mendel's work. Based on his own results, de Vries drew the same conclusions as Mendel. De Vries published his work in 1900, first in French then in German.
It is now known that de Vries had the right idea, but for the wrong reasons. Most of the variants that de Vries isolated from Oenothera lamarckiana were due to aberrant chromosomal segregations, and not to mutations associated with specific genes.


ERICH VON TSCHERMAK-SEYSENEGG (1871-1962)

Erich von Tschermak-Seysenegg was born in Vienna, Austria. His father was a well-known mineralogist, and his maternal grandfather was the famous botanist, Eduard Fenzl, who taught Gregor Mendel at one point. He studied agriculture at the University of Vienna, and worked on a farm to gain practical agricultural experience. Tschermak graduated with a doctorate from the Halle-Wittenberg University.
Tschermak was a plant breeder, and his hybridization experiments were done with the idea of improving crops using the laws of heredity. He did most of the work himself, and produced high-yielding food crops such as wheat, barley, and oats. In 1903, Tschermak was appointed associate professor at the University of Agricultural Sciences in Vienna, and later became a full professor. He has a major influence in agriculture and plant breeding in Austria.


1911

THOMAS HUNT MORGAN (1866-1945) 



Thomas Hunt Morgan established the chromosomal theory of inheritance.
Morgan had become interested in species variation, and in 1911, he established the "Fly Room" at Columbia to determine how a species changed over time. For the next 17 years, in a 16 X 23 ft. room, Morgan and his students did ground-breaking genetic research using Drosophila melanogaster, fruit flies.
In 1933, Thomas Hunt Morgan received the Nobel Prize for Medicine for his work in establishing the chromosomal theory of inheritance. He shared the prize money with his children, and those of his long-time colleagues, Alfred Sturtevant and Calvin Bridges. Although Morgan officially retired from his position at Cal Tech in 1941, he continued to work in the lab until his death in 1945.


1920 - 194

1920

HERMANN MULLER (1890-1967)

Hermann Muller showed that X-rays could induce mutations. Born in Manhattan in 1890. His father influenced Hermann with his socialist ideals and a love of science.
In the 1920s, Muller performed his Nobel prize-winning research showing that X-rays could induce mutations and he became instantly famous.
Muller's outspoken views on socialism also got him in trouble with the Texas administration. He helped publish a Communist newspaper at the school, and the FBI tracked his activities. Feeling that U.S. society was regressing during the Depression, Muller left for Europe in 1932.
Muller spent eight weeks in Spain helping the International Brigade develop a way to get blood for transfusions from recently killed soldiers, and then worked at the University of Edinburgh where he continued to work on X-rays and other mutagens like UV and mustard gas.
In 1946, Muller won the Nobel Prize for his work on mutation-inducing X-rays and he used the opportunity to continue pressing for more public knowledge about the hazards of X-ray radiation. Muller died in 1967 of congestive heart failure.


1931

BARBARA MCCLINTOCK (1902-1992)

Barbara McClintock did pioneer work in plant genetics and determined the mechanism for transposition in corn. She was born in Hartford, Connecticut. Her father was an army doctor and her mother was a piano teacher. She had a passion for information, and in a time when a woman's career was a successful marriage, McClintock was determined to go to college.
By the time she finished her undergraduate credits, she found herself in graduate school in the new field of cytology. As a paid assistant in her second year of graduate work, she improved on a method that her employer was using and was able to identify maize chromosomes. It was a problem he had been working on for years and she effectively scooped her own boss. McClintock was awarded an unshared Nobel Prize for Physiology or Medicine in 1983. McClintock was a research investigator at Cold Spring Harbor until her death in 1992.



GEORGE WELLS BEADLE (1903-1989)

George Wells Beadle 
George Beadle, "Beets" to his friends, and Edward Tatum experimentally demonstrated the "one gene one protein" hypothesis. Born in Wahoo, Nebraska, his father was a farmer. Beadle's mother died when he was four, and his father and housekeepers raised Beadle, his brother, and his sister.
Beadle's father thought he might become a farmer. However, Beadle's high school science teacher encouraged him to go to college.
Beadle and Tatum shared the 1958 Nobel Prize in Physiology or Medicine.
In 1945, Beadle accepted the Chair of the Division of Biology at Caltech, replacing T. H. Morgan who had died. After retirement in 1969, Beadle took up research again. In 1981, Beadle developed Alzheimer disease. He died in 1989. 

1941

EDWARD LAWRIE TATUM (1909-1975)


Edward Tatum was born in Boulder, Colorado. While Tatum was growing up, his family moved a number of times. His father had different teaching positions at various universities and colleges in the Midwest. Tatum grew up in a science-oriented household as his father had a Ph.D and an M.D.
Edward Tatum shared the 1958 Nobel Prize in Physiology or Medicine. And in 1958 Tatum and his student Joshua Lederberg shared the Nobel Prize in Physiology or Medicine.
Tatum died in 1975 from heart failure complicated by emphysema from a lifetime of cigarette smoking.


JOSHUA LEDERBERG (1925 - 2008)

Joshua Lederberg was born in Montclair, New Jersey, and as he said in a 1998 interview, he must have been born a scientist.
In addition to his own bacterial research, Lederberg had two other interests. One was artificial intelligence; Lederberg helped develop one of the first computer systems (DENDRAL) that could make decisions using a specific set of algorithms and a database. Lederberg's other interest was exobiology.
Lederberg's latest project is to compile an informational web site at the National Library of Medicine using archival material he has accumulated over the years.


1944

OSWALD THEODORE AVERY (1877-1955) 

Oswald Avery and Maclyn McCarty showed that Fred Giffith's "transforming principle" was DNA. Avery was born in 1877 in Halifax, Nova Scotia. His father was a Baptist minister.
During his study at Colgate University he became the leader of the college band and acquired the nickname "Babe" because of his small stature.
Avery found medical research more intellectually satisfying. Avery worked on many strains of bacteria, applying different immunological and chemical methods. In 1913, Avery published a clinical study of the tuberculosis bacterium.
In 1954, he was diagnosed with liver cancer. Avery died the following year after a painful illness.

 

EVELYN WITKIN (1921 - )

A native New Yorker, Evelyn Witkin was a pioneer in the field of biological responses to DNA damage, Witkin made history in the mid-1940s with her first experiments. She identified a strain of E. coli bacteria known as B/r that was more resistant to radiation than the parental B strain. This was the first time mutations conferring resistance to radiation had been isolated. Witkin's research focused on how bacteria could repair DNA damage caused by ultraviolet (UV) radiation.
Evelyn Witkin has received numerous honors and awards in recognition of her achievements, including election to the National Academy of Sciences in 1977. Her current passion involves finding connections between two of her favorite Victorians, Robert Browning and Charles Darwin.

Early 1950s

1950 

ERWIN CHARGAFF


He isolated DNA from different organisms and measured the levels of each of the four nitrogenous bases. The nucleotides must be arranged so that there are about equal amounts of A (adenine) and T (thymine), and about equal amounts of G (guanine) and C (cytosine) (Chargaff's ratios).


1952

ROSALIND ELSIE FRANKLIN (1920-1958)

Rosalind Franklin produced the X-ray crystallography pictures of BDNA which Watson and Crick used to determine the structure of double-stranded DNA. She was born in London, England. Her family was well-to-do. Rosalind Franklin was extremely intelligent and she knew by the age of 15 that she wanted to be a scientist. Her father actively discouraged her interest since it was very difficult for women to have such a career.
She published a number of papers and she did a lot of the work while suffering from cancer. She died from cancer in 1958.
In 1962, the Nobel Prize in Physiology or Medicine was awarded to James Watson, Francis Crick, and Maurice Wilkins (her colleges) for solving the structure of DNA.


ALFRED DAY HERSHEY (1908-1997)

Alfred Hershey and Martha Chase did the Hershey-Chase blender experiment that proved phage DNA, and not protein, was the genetic material. Alfred Hershey was born in Owosso, Michigan. In 1946, working with Delbrück, Hershey discovered that phage can recombine when co-infected into a bacteria host. This led to a new area of phage genetics.
As leading researchers in the field of bacteriophage, Delbrück, Luria, and Hershey established the American Phage Group which had a tremendous influence on bacteriophage research.
Hershey shared the 1969 Nobel Prize for Physiology and Medicine with Max Delbrück and Salvador Luria.

1953

LINUS PAULING

Linus Pauling proposed a triple-stranded helix sructure for DNA.      



Late 1950s

1955
 
FRANCIS HARRY COMPTON CRICK (1916-)
Besides coming up with the double helix structure for DNA with James Watson, Crick also proposed the Central Dogma and Adaptor Hypothesis. Francis Crick was born in a small town near Northampton, England.
As a child, Crick was very inquisitive and he read all of the books of Children's Encyclopedia that his parents bought him.
Francis Crick, James Watson and Maurice Wilkins shared the 1962 Nobel Prize for Physiology or Medicine for solving the structure of DNA.
Crick and some of his fellow scientists, including James Watson, were members of the informal "RNA tie club," whose purpose was "to solve the riddle of RNA structure, and to understand the way it builds proteins."
In 1961, Francis Crick and Sydney Brenner provided genetic proof that a triplet code was used in reading genetic material.



JAMES DEWEY WATSON (1928-)

James Watson and Francis Crick came up with the structure for DNA. Watson was born in Chicago.
In 1962, Watson shared the Nobel Prize for Physiology or Medicine with Francis Crick and Maurice Wilkins who, with Rosalind Franklin, provided the data on which the structure of DNA was based.
Watson has played a significant role in the development of science policy, from the War on Cancer, through the debates over the use of recombinant DNA, to promoting the Human Genome Project.
One of his major interests is education. His first textbook, "Molecular Biology of the Gene," set new standards for biology textbooks, and it was followed by "Molecular Biology of the Cell," and "Recombinant DNA".
He is actively exploring the avenue of multimedia education. He was and is one of the main motivators of the project: DNA from the Beginning. 


1954

SEYMOUR BENZER (1921-2007)

Seymour Benzer was born in 1921 and grew up in the Bensonhurst neighborhood of Brooklyn, NY. His parents emigrated from Warsaw, Poland and worked in the garment industry. Although his family was not interested in science, Benzer dissected flies in his basement lab and read books on atomic physics during synagogue.
Benzer spent most of his time travelling to other labs to work in molecular biology.
In 1971, Benzer received the Lasker Award for this "brilliant contribution to molecular genetics."
As a professor of biology at Caltech, he and his graduate student Ronald Konopka were the first to find a gene that controls an organism's sense of time. Benzer received the Crafoord Prize in 1993 for his pioneering work in genes and behavior.



1956

PAUL CHARLES ZAMECNIK (1913- ) 

Paul Zamecnik and Mahlon Hoagland determined the identity of Crick's adaptor molecule, tRNA.
Although Zamecnik trained to be a medical doctor, he was always interested in science. He eventually decided to go into research because there was so much to discover.
His interest in protein synthesis started with a question. In 1938, as an intern, Zamecnik was doing an autopsy on an obese woman. He wondered why there was fat when there should have been protein and muscle - no one knew the answer.
In 1952, Zamecnik was partially successful in that he made a cell-free extract from rat liver with which he was able to synthesize proteins from amino acids. In 1953, using this system, Zamecnik and Mahlon Hoagland showed that amino acids had to be energized, "activated," by ATP before they were incorporated into a peptide chain.
In 1960, his lab developed a cell-free extract from the bacteria E. coli. He shared the preparation method with other scientists. Marshall Nirenberg and Johann Matthaei used the cell-free extract from E. coli to crack the genetic code.
In 1978, he made another interesting observation. He found that oligonucleotides were able to enter cells. This led to a new area of research and possible therapy.
Zamecnik still runs a lab at Massachusetts General Hospital and is a Professor Emeritus at Harvard University.



MAHLON HOAGLAND (1921- )

Mahlon Hoagland was born in Boston. His father was a research scientist with an interest in neurobiology.
In 1953, Hoagland started work in Zamecnik's lab on the problem of amino acid activation.
He then began working on a project that Zamecnik had put on hold. This led to the discovery of tRNA, the adaptor (predicted by Francis Crick) that shuttles amino acids to messenger RNA. The results were published in 1957 and served to connect two fields of science research, biochemistry and molecular biology.
Although Hoagland is now retired, he still has a strong interest in education and teaching. Over the years, he has written a number of "non-scholarly" books on the subject of genes and molecular biology.


1957

MATTHEW STANLEY MESELSON (1930-) 
 
Meselson and Stahl experimentally proved Watson and Crick's model of semi-conservative replication. Matthew Meselson was born in Denver, Colorado. He had always wanted to be a chemist.
Meselson's and Stahl's "classic" paper was published in 1958 and their experiment has been called "one of the most beautiful experiments in biology."
He discovered the enzymatic basis of host DNA protection, where the cell recognizes its own DNA by adding methyl groups to it.
Meselson also discovered the process of DNA mismatch repair, which allows cells to fix mistakes in DNA.
Since 1963, Meselson has been concerned about the use of chemical and biological weapons in warfare.


FRANKLIN WILLIAM STAHL (1929-)

 
 Franklin "Frank" Stahl was born in Boston.
In 1957, Stahl and Meselson developed the technique of density gradient centrifugation and used it to prove that DNA was replicated in a semi-conservative way, as predicted by Watson and Crick in their 1953 paper.
In 1959, Stahl accepted a position at the University of Oregon where he is now a distinguished professor of Molecular Biology. His current research interest is on the mechanisms of genetic recombination.



ARTHUR KORNBERG (1918- )



Arthur Kornberg was born in Brooklyn, New York. His parents emigrated from Eastern Europe and neither of them had a formal education. Kornberg's parents believed that education was very important and encouraged their children to stay in school. Kornberg was an excellent student.
He was mostly involved in research on nutrition and metabolic reactions. He isolated DNA polymerase I and show that life (DNA) can be made in a test tube.
In 1959, Kornberg shared the Nobel Prize for Physiology and Medicine with Severo Ochoa-Kornberg for the enzymatic synthesis of DNA, Ochoa for the enzymatic synthesis of RNA.
Over the years, Kornberg isolated and identified over a hundred enzymes used in metabolic reactions.
Kornberg enjoys teaching and has written a textbook on DNA replication as well as an autobiography on his experiences as a scientist. He sees science as a 'creative activity' and an 'art form'. 


1960s

1961

SYDNEY BRENNER (1927- )


Sydney Brenner was born in Germiston, South Africa.
In 1957, Brenner, Seymour Benzer, Francis Crick, and Leslie Barnett published a paper in Nature on the fine mapping of mutations in phage. Brenner then moved onto the problem of how the information was transferred between DNA and protein. In 1960, Brenner, François Jacob, and Matthew Meselson designed and worked on another series of experiments establishing the existence and function of messenger RNA.
In 1998, with a donation from tobacco giant Phillip Morris, Brenner established and is the director of the Molecular Science Institution (MSI) in Berkeley, California. 



MARSHALL WARREN NIRENBERG (1927-)

Nirenberg shared the 1968 Nobel Prize for Physiology or Medicine with Har Gobind Khorana and Robert Holley for cracking the genetic code. Originally born in New York City.
In 1961, Nirenberg and J. H. Matthaei published their landmark paper. They showed that a synthetic messenger RNA made of only uracils can direct protein synthesis. The polyU mRNA resulted in a poly-phenylalanine protein - they had the first piece of the genetic code.
In subsequent years, Nirenberg and his group deciphered the entire genetic code by matching amino acids to synthetic triplet nucleotides.
Nirenberg and his group also showed that with few exceptions, the genetic code was universal to all life on earth.



FRANÇOIS JACOB (1920-)

François Jacob grew up in Paris. Jacob attended medical school until the impending German invasion forced him to flee to England in 1940.
Jacob and Monod's unraveling of the lac operon not only introduced the new concept of regulatory sites on DNA, but also the concept of mRNA. Jacob worked with Sydney Brenner to verify the hypothesis.







JACQUES LUCIEN MONOD (1910-1976) 
 
Jacques Monod and François Jacob were the first to discover how genes were turned on and off. Jacques Lucien Monod was born in Paris but he grew up in sunny Cannes, home to the Cannes Film Festival. By age 16, he decided to become a biologist.
Arthur Pardee, François Jacob, and Monod's studied how bacteria make an inhibitor to keep beta-galactosidase production turned off.
By the time the lac operon system was worked out, Monod switched his curiosity to allostery. Monod called the concept the second secret of life.
In the latter part of his career, Monod interpreted the findings of molecular biology for the general public in his book, "Chance and Necessity," and directed the Institut Pasteur. Monod died in 1976 of leukemia; his last words were "Je cherche a comprendre" (I am trying to understand.)



1965

ROY JOHN BRITTEN (1919-)

Roy Britten showed that eukaryotic genomes have many repetitive, noncoding DNA sequences. He was born in Washington D.C.
Britten has been interested in evolutionary biology, specifically the nature of repetitive DNA and its origin and evolutionary history. He is also looking at other repetitive elements in the human genome.
Britten has a number of hobbies and interests outside of science. 



 1970s

1970

DAVID BALTIMORE (1938-)
 
David Baltimore was born in New York City.
Baltimore, Temin and Renato Dulbecco shared the 1975 Nobel Prize in Physiology or Medicine for their discoveries concerning the interaction between tumor viruses and the genetic material of the cell.
Currently, Baltimore is the president of California Institute of Technology and has been since 1998.





HOWARD MARTIN TEMIN (1934-1994)



Howard Temin was born in Philadelphia.
He developed his provirus theory, which hypothesized that RSV and other RNA viruses entered the cell and then made DNA copies of themselves before integrating into the host genome.
He published his results in 1964 and in 1975 shared the Nobel Prize in Physiology or Medicine with David Baltimore and Renato Dulbecco for their discoveries concerning the interaction between tumor viruses and the genetic material of the cell.
Although Temin did not smoke, he died in 1994 from lung cancer.




1972
 
STANLEY NORMAN COHEN (1935-)
 
Stan Cohen was born in Perth Amboy, New Jersey. As a child, he was very interested in science, especially in how things worked.
While he was at the National Institutes of Health, he made the decision to combine basic research with clinical medicine. In 1968 he began experimenting with plasmids. Plasmids have clinical importance because of the drug resistance genes they carry.
Cohen worked on ways of breaking up the plasmids, and isolating usable fragments for cloning.
Cohen is a Professor of Genetics at Stanford University. He is a member of the National Academy of Sciences, and in 1980, won the Albert Lasker Basic Medical Research Award. He was awarded the National Medal of Science in 1988.



Herbert W. Boyer (1936-) 

Herb Boyer was born in Derry, Pennsylvania.
At a conference in Hawaii in the early '70s, Boyer met Stanley Cohen who was working on plasmids. The two began a collaboration that eventually led to the creation of the first recombinant DNA.
He and Cohen have won numerous awards for their discovery: 1996 Lemelson-MIT Prize for Invention and Innovation, 1993 Swiss Helmut Horten Research Award, and 1980 Albert Lasker Basic Medical Research Award, among others.



Maxine Singer 

Maxine Frank Singer, President of the Carnegie Institution of Washington, NIH intramural scientist, and distinguished member of the National Academy of Sciences, is also a tireless and eloquent advocate for biomedical research.
Singer's scientific focus has progressed from experiments on the synthesis and structure of RNA and the genetic code, to work on animal viruses, to defective SV40 viruses in monkey cells.
Her current research springs from her discovery of a transposable element in human DNA.
Singer has won many awards and honorary degrees, not only for her scientific work but for her science advocacy and community service as well. 



1974

Richard John Roberts (1943-)
 
Richard (Rich) Roberts was born in Derby, England.
In 1972 James Watson offered Roberts a position at Cold Spring Harbor Laboratory. Roberts accepted the position and started investigating the enzyme Endonuclease R which he heard about from Dan Nathans. The enzyme cut DNA into specific pieces. During the '70s and early '80s, about 75 out of 100 known enzymes were isolated in Roberts' lab.
Some of these restriction enzymes were used to map adenovirus DNA, a project in which Phil Sharp, in Joe Sambrook's lab, was also involved. Through the course of their experiments, they discovered biochemical proof that the genes in adenovirus were split. In 1993, Roberts shared the Nobel Prize in Physiology or Medicine with Phil Sharp for the discovery of the split gene.
Roberts also helped develop one of the first computer programs that maps and analyzes DNA restriction enzyme fragments. He was an early advocate of computer use in molecular biology.



Phillip Allen Sharp (1944-)
 
Phillip (Phil) Sharp was born in Kentucky.
Sharp worked with and studied bacterial plasmids. Sharp was interested in gene expression and worked with simple viruses, like SV40 and adenovirus. Sharp mapped the adenovirus genome. He and his colleagues then mapped the adenoviral mRNAs and linked them to function. Sharp shared the 1993 Nobel Prize for Physiology or Medicine.
In 1978, Sharp and a group of other scientists, including Walter Gilbert, founded Biogen Inc., one of the first biotech companies. It is now centered in Boston.
In addition to the Nobel, Sharp has won numerous prizes for his work.



1975

Roger Kornberg (1947-)
 
Roger Kornberg figured out the importance of histones to chromatin structure. With both parents being well-respected scientists, it was not surprising that Roger Kornberg developed an interest and an enthusiasm for science.
Kornberg studied chemistry and biochemistry, and without having to think about it, became a scientist.
In 1978, he moved to Stanford University where he is now professor of structural biology.
Over the past 35 years, Kornberg has published over 150 research papers on phospholipid and chromatin structure, gene regulation and transcription control.


Frederick Sanger (1918-)
 
Frederick Sanger was born in Rendcombe, England.
He was the first person to obtain a protein sequence. Sanger won his first Nobel Prize for Chemistry in 1958 for his work on the structure of protein.
Solving the problem of DNA sequencing became a natural extension of his work in protein sequencing. Sanger initially investigated ways to sequence RNA because it was smaller. Eventually, this led to techniques that were applicable to DNA and finally to the dideoxy method most commonly used in sequencing reactions today. Sanger won a second Nobel Prize for Chemistry in 1980 sharing it with Walter Gilbert, for their contributions concerning the determination of base sequences in nucleic acids, and Paul Berg for his work on recombinant DNA.



1980s

Leland Hartwell (1939-) 

Lee Hartwell was born in Los Angeles.
After his Ph.D., Hartwell went to the Salk Institute because he wanted to work with Renato Dulbecco. Hartwell already knew he wanted to work on cell division, which was one of Dulbecco's research interests.
He also made the rather risky decision to start using yeast as a model system. Not many people were using yeast at the time, but Hartwell wanted and needed a simpler experimental system to study basic questions of cell growth. Hartwell is a pioneer in yeast genetics, and has used yeast to identify many of the genes involved in protein synthesis as well as the cell cycle.
His lab works on the molecular mechanisms that maintain and support gene variations, which can eventually lead to the evolution of new species.
In 2001, Leland Hartwell shared the Nobel Prize in Medicine and Physiology with Timothy Hunt and Paul Nurse for their discoveries of key regulators of the cell cycle.



Christiane Nüsslein-Volhard (1942-)
 
Christiane (Janni) Nüsslein-Volhard was born in Frankfurt, Germany during World War II.
When she finished her Ph.D. in 1974, she wanted a new challenge and began to investigate the idea of using genetics to study developmental problems. She read a review about some Drosophila mutants and became interested in the bicaudal mutation.
She learned to screen for mutants and developed techniques to analyze the mutations.
In 1978, Nüsslein-Volhard accepted a job at the new European Molecular Biology Laboratory in Heidelberg. Eric Wieschaus was hired at the same time. The two began working together to analyze embryonic Drosophila mutants and developed a screen to isolate new mutations. Nüsslein-Volhard and Wieschaus shared the 1995 Nobel Prize with Ed Lewis for their work in Drosophila development.


Eric Francis Wieschaus (1947-) 

Eric Wieschaus was born in South Bend, Indiana in 1947.
In 1978, Wieschaus was offered a job at the newly established European Molecular Biology Laboratory (EMBL) in Heidelberg. Nüsslein-Volhard had been offered a job there as well, and the two of them were able to collaborate on the experiments they had talked about in Basel. They carried out large-scale mutagenesis experiments to find developmental Drosophila mutants. The result of their work was a new understanding of the mechanism involved in early Drosophila development. Wieschaus and Nüsslein-Volhard shared the 1995 Nobel Prize for their work with Ed Lewis.
In 1981, Wieschaus accepted a position at Princeton University and he has been there ever since. His research continues to focus on development, specifically on changes in cell shape during the various developmental stages.


Kary Mullis (1944- ) 

Kary Mullis was born in Lenoir, North Carolina.
In 1979, Mullis joined the Cetus Corporation outside of San Francisco, California, as a DNA chemist. He spent seven years there, during which he carried out research on the synthesis of oligonucleotides. While at Cetus, Mullis invented the polymerase chain reaction (PCR), a technique that amplifies specific DNA sequences from very small amounts of genetic material.
PCR has revolutionized DNA technology by allowing scientists to produce an almost unlimited amount of highly purified DNA molecules suitable for analysis or manipulation. The monumental significance of PCR was recognized in 1993, with Mullis receiving a Nobel Prize in chemistry.



Alec Jeffreys 

Sir Alec Jeffreys's involvement with mammalian molecular genetics began in 1975, when, as a postdoc, he moved from Oxford University to the University of Amsterdam to work with Dick Flavell. There, the two and their colleagues tried to clone a mammalian single-copy gene.
In 1983, Jeffreys found that the repeat sequences, dubbed "minisatellites," contain certain "core" sequences. This opened the way for the development of probes, containing the core sequences, for detecting many other such regions of variable DNA.





1989

Thomas Robert Cech (1947-)
 
Thomas (Tom) Cech was born in Chicago and grew up in Iowa City.
In 1978, Cech accepted a position in the Department of Biochemistry at the University of Colorado, Boulder. It was here that he and his research group did the work leading to the discovery that RNA can self-splice and thus can act as a ribozyme. For this discovery, Cech shared the 1989 Nobel Prize for Chemistry with Sidney Altman.
Among his many honors and awards, Cech received the 1995 National Medal of Science.




Sidney Altman 

He was born in Montreal in 1939.
Nobel Winner 1989 shared with T. R. Cech for Chemistry for discovery that RNA can self-splice and thus can act as a ribozyme.






Mario Renato Capecchi (1937-) 

In college at Antioch, Capecchi began studying for a political science degree to combine his esteem for science with his sense of social responsibility. But he found little science in politics and abandoned it for physics and chemistry.
In 1996, he received the Kyoto Prize honoring his lifetime achievement in the betterment of humanity.




1990 - 2000

Howard Robert Horvitz (1947- ) 

Bob Horvitz was born in Chicago, Illinois.
Horvitz was interested in neurobiology, but because of his limited experience with biology in general, he started working with phage (a virus that infects bacteria), to learn the basics.
He has won a number of awards for his work including the 1999 Gairdner Foundation Award. Horvitz is a co-founder and Chairman of Idun Pharmaceuticals Inc., a biotech company based in La Jolla, California that is developing therapeutics focusing on apoptosis.
He shared the 2002 Nobel Prize in Physiology or Medicine with colleagues John Sulston and Sydney Brenner. All three made major contributions in the field of developmental biology using the model organism Caenorhabditis elegans.



Mary-Claire King (1946- )
 
Born in a suburb of Chicago.
With her background in genetics and a personal interest in cancer, King then turned her attention to analyzing the pattern of breast cancer in families. Her findings suggested that the disease might be inherited in some cases, and she set herself the ambitious goal of finding the genes responsible for inherited breast cancer. In 1990, King and her colleagues proved the existence of the first gene to be associated with hereditary breast cancer, now known as BRCA1.
She received the Clowes Award for Basic Research from the American Association for Cancer Research, the Brinker Award from the Komen Foundation, and was a Glamour magazine "Woman of the Year".



1995
 
Stephen P. A. Fodor (1953-) 

Steve Fodor was born in Seattle, Washington.
He was put in charge of developing a process to generate miniature high-density arrays of biological compounds. This led to the development of the first DNA GeneChip®, and the techniques to read and analyze these chips for large-scale genomic studies. He and his colleagues received the AAAS' 1992 Newcomb Cleveland Award for this work.
He has won numerous awards for his work on and the development of GeneChip® including the 2002 Takeda Foundation Award, the 2002 Economist Innovation Award for Nanotechnology, and the 2002 Oxford Bioscience Award.



2000
 
Patrick Henry Brown (1954-) 

Pat Brown was born in Washington, D.C.
He began to think of this idea as a DNA array - laying down DNA samples into columns and rows.
From the very beginning of this project, Brown had a very clear vision of what was needed. His first collaboration with an engineer failed because the mechanization of producing a DNA array became too "engineered."
Later with computerized automation, these DNA arrays can hold up to 80,000 samples - more than the estimated total number of genes that make up a human being.
In 1995, Brown published the first of many papers that use DNA arrays to analyze patterns of expression. He had held workshops on how to build DNA arrays and has made the protocols available at his web site.



John Craig Venter (1946-) 

Craig Venter began the race to sequence the human genome when he unexpectedly announced to a room full of genome researchers that they could just quit now, thank you, because his company would finish the job.
John Craig Venter was born in 1946 in Salt Lake City.
In the early 1990s, Venter developed the EST method of finding genes.
As he turned his focus to the human genome, Venter left TIGR and started the for-profit company Celera, a division of PE Biosystems, the company that makes the latest and greatest sequencing machines. Using these machines, and the world's largest civilian supercomputer, Venter finished assembling the human genome in just three years.



Francis Collins (1950-)
 
If sequencing the human genome is the Holy Grail of biology, then Francis Collins is its King Arthur. Collins has overseen the mapping, the sequencing, and the funding of biology's first "big science" project as the Director of the National Human Genome Research Institute since 1993.
At Yale, Collins began working on ways to search the genome for genes that cause human disease.
In 1989 Collins had his first big success with the method when he pinpointed the gene that causes cystic fibrosis. He continues to search for disease genes at NIH.



John Sulston (1942 -)
 
Born in Cambridge, England.
Sulston had his first big breakthrough in 1976, when he described the cell lineage for a part of the developing nervous system of C. elegans, mapping the neuronal circuitry and the migratory pathways of the entire nervous system. He also showed that every member of the species undergoes exactly the same program of cell division and differentiation.
Staring into the microscope in two four-hour shifts per day for 18 months, Sulston was able to track every cell that was born and died in the 14 hours. Through this work, Sulston built a cell-fate map of C. elegans, enabling other scientists to compare and use mutants to find genetic defects. He completed this work in the early 1980s, and soon moved on to trying to sequence the entire genome of C. elegans.
Sulston was offered huge amounts of money to sequence and patent genes, but he refused on both moral and scientific grounds. He believes it is morally wrong to patent genes as they are not invented, and scientifically wrong as it blocks the advancement of knowledge. Sulston instead chose to work on a publicly funded sequencing project as director of the Sanger Center, making his data freely available as soon as he had it. Nobel Winner 2002.