Page 138 - 86 human physiology part-2

Genetics and Inheritance

Pea plant reproduction is easily manipulated. They have both male and female parts and can easily
be grown in large numbers. For this reason, pea plants can either self-pollinate or cross-pollinate with
other pea plants.

In cross pollinating two true-breeding plants, for example one that came from a long line of yellow
peas and the other that came from a long line of green peas, the first generation of offspring always
came out with all yellow peas. The following generations had a ratio of 3:1 yellow to green. In this and
in all of the other pea plant traits Mendel observed, one form was dominant over another so it masked
the presence of the other allele. Even if the phenotype (presence) is covered up, the genotype (allele)
can be passed on to other generations.

Time line of notable discoveries

1859 Charles Darwin publishes "The Origin of Species"
1865 Gregor Mendel's paper, Experiments on Plant Hybridization
1903 Chromosomes are discovered to be hereditary units
1906 The term "genetics" is first introduced publicly by the British biologist William Bateson at
the Third International Conference on Genetics in London, England
1910 Thomas Hunt Morgan shows that genes reside on chromosomes, and discovered linked genes
on chromosomes that do NOT follow Mendel's law of independent allele segregation
1913 Alfred Sturtevant makes the first genetic map of a chromosome
1913 Gene maps show chromosomes contain linear arranged genes
1918 Ronald Fisher publishes On the correlation between relatives on the supposition of
Mendelian inheritance - the modern synthesis starts.
1927 Physical changes in genes are called mutations
1928 Fredrick Griffith discovers a hereditary molecule that is transmissible between bacteria
1931 Crossing over is the cause of recombination
1941 Edward Lawrie Tatum and George Wells Beadle show that genes code for proteins
1944 Oswald Theodore Avery, Colin McLeod and Maclyn McCarty isolate DNA as the genetic
material (at that time called transforming principle)
1950 Erwin Chargaff shows that the four nucleotides are not present in nucleic acid in stable
proportions, but that some general rules appear to hold. (e.g., the nucleotide bases Adenine-
Thymine and Cytosine-guanine always remain in equal proportions)
1950 Barbra McClintock discovers transposons in maize
1952 The Hershey-Chase experiment proves the genetic information of phages (and all other
organisms) to be DNA
1953 DNA structure is resolved to be a double helix by James D. Watson and Francis Crick, with
help from Rosalind Franklin
1956 Jo Hin Tjio and Albert Levan established the correct chromosome number in humans to be
46
1958 The Meselson-Stahl experiment demonstrates that DNA is semi-conservatively replicated
1961 The genetic code is arranged in triplets
1964 Howard Temin showed using RNA viruses that Watson's central dogma is not always true
1970 Restriction enzymes were discovered in studies of a bacterium Haemophilus influenzae,
enabling scientists to cut and paste DNA
1977 DNA is sequenced for the first time by Fred Sangr, Walter Gilbert, and Allan Maxam
working independently. Sanger's lab complete the entire genome of sequence of Bacteriophage
1983 Kary Banks Mullis discovers the polymerade chain reaction enabling the easy amplification
of DNA

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