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bild 3 lecture 4 - It was found early in the twentieth...

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It was found early in the twentieth century that these characters have a genetic component, and that the genes contributing to them are often inherited as codominant Mendelian characters. aa bb cc AA BB CC Aa Bb Cc aa bb cc AA BB CC Aa Bb Cc AA Bb cc AA bb Cc Aa BB cc aa BB Cc Aa bb CC aa Bb CC Aa bb cc aa Bb cc aa bb Cc AA bb cc aa BB cc aa bb CC Aa Bb cc Aa bb Cc aa Bb Cc AA BB cc aa BB CC AA bb CC AA Bb Cc Aa BB Cc Aa Bb CC AA BB Cc Aa BB CC AA Bb CC ears ears Centimeters # of (capital letter) alleles that add length to the ear 0 1 2 3 4 5 6
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Demonstration that ear length in corn is controlled by Mendelian genes. The genotypes at the bottom of the figure are those that would be expected in the F 2 if the character were controlled by three unlinked codominant genes, with each capital letter allele adding 2 cm to the ear length. 3) How is genetic variation preserved in populations? The great strength of the neo-Darwinian synthesis was that it explained how selectable genetic variation, in the form of genetic polymorphisms (different alleles of genes in populations), could be preserved for many generations in populations. Because the polymorphisms are preserved, they are available during all that time for natural selection to act on and to change allele frequencies at polymorphic loci. For example, “small dog” alleles may be present at low frequencies in wolf populations (this is not yet known). If they were, their presence would have made selection for small dogs by our Neolithic and early agriculturist ancestors easier. Genetic polymorphism:
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Note that no single organism in this diploid population can have more than two alleles at a locus, even though there may be more than two alleles at that locus in an entire population. The Hardy-Weinberg Law and Factors that Disturb Hardy-Weinberg Equilibrium The reason the genetic variation can be preserved for many generations is because polymorphic genes tend to obey the Hardy-Weinberg Law .
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