Gen.Class+notes_3 (1)

Gen.Class+notes_3 (1) - • Gregor Mendel(1822-1884 studied...

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Unformatted text preview: • Gregor Mendel (1822-1884) studied and discovered the principles of heredity. • Experiments on heredity have been done since the dawn of civilization: farming and husbandry. • In Mendel’s time several people were studying heredity but they described their observations qualitatively. • The key idea was that there was a regularity were after fertilization a trait will reappear in the progeny. Thus there must be a law governing this behavior. • Mendel understood that in order to clearly define the rules of inheritance, a careful and detail study must be done. • Numbers (several progeny) and a rigoruos statistical analysis of more than one variety of plant was important. • Plants were chosen because they give great numbers of progeny, the generation time is not too long and there is no special equipment needed besides a garden. • The characteristics important to Mendel were : 1) The plant must possess constant differentiating characteristics. 2) The hybrids should be protected from foreign pollen 3) The hybrids and their offspring should not suffer decreased fertility. 1) The plant must possess constant differentiating characteristics . •) Mendel choose seven traits of the pea plant Pisum sativum . •) He focus on characteristics that were clear cut: two different forms only. •) He avoided traits that had a range of variation and thus unwittingly he avoided more complicated modes of inheritance. Dominance : It only requires one allele to determine the phenotype. The allele in capitals ( R ) is the dominant allele. Recessiveness : It requires two alleles to show the phenotype. The allele in lower case ( r ) is the recessive allele. What does R and r denotes? If you know the genotype then you can tell what the phenotype is. BUT if you know the phenotype you can not tell what the genotype is. Let R code for round seeds and r code for wrinkle seeds. If you know the genotype Genotype phenotype RR you get round seeds Rr you get round seeds rr you get wrinkle seeds But if you know that the phenotype is round seeds , the genotype could be RR or Rr . Mendel made sure these plants breed true All the progeny were round seed!...
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Gen.Class+notes_3 (1) - • Gregor Mendel(1822-1884 studied...

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