Biology 3300- Positive Selection & Reproduction

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BIOL 3300
Theresa Burg

Biology 3300 th Feb.5 , 2014 Positive Selection: - Favors the advantageous mutation - G6PD on X chromosome o 100’s of alleles with most of them decreasing the efficiency of the enzyme o Varying effects  Severe effects  hemolytic anemia  Allele 202A, possible malarial resistance o 18% in 3 African populations o 230 males, 9 alleles with 11 point mutations - The map shows the frequency of deficient males across the world o As can be seen the most amount of males deficient of G6PD are found in African countries - There is selection for individuals that are carriers, positive selection increases the frequency of the disease If G6PD-202A is under positive selection, what would the distribution look like? - 3 Outcomes if the mutation is neutral: high frequency (dark blue line), low frequency (aqua line), and disappears (red line) - Of recent positive selection the allele has had a high frequency and high linkage equilibrium - Extended haplotype homozygosity (EHH) is a measure of linkage with specific haplotypes - G6PD-202A does NOT go into equilibrium - Positive selection increases the frequency of the allele - If ab is missing in a population, Ab and aB will have to undergo recombination to eventually bring back ab. This is not a rapid process, it takes a lot of time. Examples of recent positive selection: - Sperm mobility and fertilization - Carbohydrate metabolism - Olfaction - Lactase Population mutation-drift equilibrium: - Young, rare alleles have high linkage disequilibrium - Old, rare alleles have low linkage disequilibrium - Old, common alleles have low linkage disequilibrium Asexual  exact copies of parents Unisexual  lineages predominately female Sexual  each contributing ½ genome Asexual  depends on conditions - ex: aphids Asexual Reproduction - Advantages: o 100% of genetic info is passed on o If parent is well adapted to its environment, then the offspring will be adapted too o No need to find a mate. Finding a mate is harder when there is a lower population density - Disadvantages: o No recombination o Increase in mutation o Decrease in genetic variation Unisexual Reproduction - Parthenogenesis  produces diploid eggs that are identical of mother. No male is needed o Ex: lizards and salamanders - Gynogenesis  A male is needed to prod
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