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Gregor Mendel
Gregor Mendel, an Augustinian monk, became known as the "father of genetics." This is for many good reasons, starting with his findings after crossing abnormal pea plants. First, he self-pollinated pea plants (P generation.) Next, he cross-pollinated the P gen., and it became known as the F1 generation. After that, the F1 gen. self-pollinated, and became known as the F2 generation. His results after doing this were way ahead of his time. Next, we'll examine Mendel's findings/ contributions. -
Mendel Cont.
Based on all of his tests, we can now conclude that many factors influenced how traits were passed down. Mendel found that traits were inherited in certain ratios, and that dominance and segregation played roles in the development of traits.The Law of Segregation stated that when gametes are produced, copies of genes separate so that each gamete only receives one copy. The Law of Ind. Assort. stated that there was no relation between how traits were inherited. They are inherited independently. -
William Bateson and Reginald Punnett Cont.
punnett square, which showed the probability of an offspring to inherit a certain pair of alleles from their parents. Bateson was credited with thinking of scientific terms like genetics, zygote, heterozygote, and homozygote. He also influenced scientists in the future to continue genetic research, as did Punnett. -
William Bateson and Reginald Punnett
William Bateson and Reginald Punnett discovered inheritance patterns that differed from those of Gregor Mendel. They published the first account of gene linking, after experimenting with sweet peas, and finding out that some traits were inherited together. This, of course, was due to the genes being located closely together on the same chromosome. After examing flower color and pollen shape, they were able to conclude that gene linkage had occured. Punnett was also credited for developing the -
Thomas Hunt Morgan
Morgan began his research as a means to get definite answers. He was skeptical about some of Mendel's findings since they were based mainly off of observations. He began his experiments by breeding an unusual white-eyed male fly with "wild type" (red-eyed) females, and found that all of the F1 flies had red eyes. When he crossed the F1 together, there were some white eyed F2 flies, but all male. Morgan figured out the answer was in the X chromosome and that it actually carred genetic material. -
Thomas Hunt Morgan Cont.
Morgan continued his research on flies, and figured out that traits or "genes" were arranged on chromosomes, but were not always inherited together. Sometimes, chromosomes crossed over, with one chromosome exchanging genes with another chromosome. This important discovery showed how genetic diversity happened. -
Archibald Garrod
Archibald Garrod experimented with inherited diseases. He carefully studied Alkaptonuria, which is caused by a build-up of a protein called alkapton. It is normally broken down by the body. His experiments showed that the gene for Alkaptonuria was recessive, by the Mendelian genotypic ratio (1:2:1). He continued studying other metabolic disorders, and saw that a deficiency in the ability to produce certain enzymes would lead to diseases. This was his major contribution to genetics. -
Frederick Griffith
Griffith extensively researched the bacteria which could cause pneumonia. He realized that seemingly harmless strains of a bacteria (R-strain) when mixed with a harmful S-strain, would be potentially fatal. His first experiment was performed on mice, which he injected with a heated form of the S-bacteria. This mice lived on! However, when he injected a mixture of the R-strain and heat-killed S-strain into the mice, they ended up dying. -
Frederick Griffith Cont.
This happened because when mixed, the R-strain was "transformed" into the S-strain by picking up the S-strain's DNA. Griffith's major contribution to the world of genetics was in his finding of bacterial transformation. -
George Beadle and Edward Tatum
Beadle and Tatum used mutant bread molds to explain the theory of one gene--one enzyme. They used radiation to make mutant strains of a bread mold. Each mutant required a different nutrient to survive, which led them to believe that different genes were mutated. Other experiments led the two scientists to believe that the genes coded for different enzymes. Later modified to one gene--one polypeptide, this principle said that more than one gene could contribute to the making of a single enzyme. -
Erwin Chargaff
Chargaff's Rules, as they later became known, consisted of 2 parts. The first was that in DNA, the amount of guanine = the amount of cytosine, and that the amount of adenine = the amount of thymine units. The second part of Chargaff's Rules is in the fact that different species have different amounts of A+T or G+C. -
Maurice Wilkins and Rosalind Franklin
These two geneticists set out to answer the unknown question of what DNA looked like. To do this, they'd use a technique called X-ray crystallography.Through many trial and errors, Franklin and Wilkins figured out that the sugar-phosphate backbone of DNA is located on the outside of the molecule, verses where others thought it was located (inside). Another discovery made was in the structure of DNA itself. It was found that DNA had two strands, verses the previously thought 3 strands. -
Alfred Hershey and Martha Chase
These two scientists performed a series of experiments to confirm that DNA was the genetic material. To do this, they made radioactive phage DNA and infected bacteria. When they separated the phage and bacteria by centrifuging the mixture, the radioactivity went with the bacteria. Since the phage inject their DNA into the bacteria, then this proved that the DNA must have been the genetic material, not the protein. -
Maurice Wilkins and Rosalind Frankling Cont.
The most well known discovery that this pair made was the finding that DNA was a double helix structure. These results weren't published until a later date, after Watson and Crick also worked out the dougle helix structure, and published a final report on what DNA really did look like. -
James Watson and Francis Crick
Rosalind Franklin, who had passed away because of cancer, also helped Watson and Crick to determine the structure of DNA. They used Franklin's X-ray "pictures" to determine that the shape of DNA was a double helix. They received the Nobel Prize for that discovery. -
Marshall Nirenberg
Even with all of the new discoveries, two questions still remained unanswered. These were: how was DNA tied to proteins, and what role did RNA play in the process? Nirenberg and his team of scientists broke the genetic code by adding different sequences of RNA to a mixture of busted open bacteria, along with a mixture of amino acids, one of which was radioactive. By changing which amino acid was ratioactive, they figured out which RNA sequence was tied to which amino acid and the role of RNA.
