In this system the balance of opposing selection coefficients at different levels should give an equ

In this system the balance of opposing selection coefficients at different levels should give an equ

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In this system the balance of opposing selection coefficients at different levels should give an equilibrium allele frequency of 0.7 for f(t) allele (using data not provided here). In nature f(t) = 0.36. Discrepancy due to small local groups and drift . Some local breeding groups (2 - 4 individuals) fixed for the t allele and since tt is sterile, these demes go extinct reducing the f(t). Thus we have selection at three levels : genic, individual and intergroup all contributing to the maintenance of the t/T polymorphism. Would we expect to detect meiotic drive systems in natural populations? If a new mutation arose that introduced a bias in the transmission of the chromosome on which it was located, then it would sweep to fixation and the locus would be homozygous for the "drive" allele. Meiotic drive can only be detected in heterozygous
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Unformatted text preview: state, so the drive system would disappear when the drive allele went to fixation. There will be a window of time where the allele is increasing in frequency, but this could be short-lived. If the drive allele reduced viability in the homozygous state (as the T locus example), then variation can be maintained and the drive system would persist longer, making it more likely to be detected. Another case where genic selection may act: sex ratios. Why should the sex ratio be 1:1 in most diploid species? Assume a sex ratio of 40% males and 60% females. Males in this case are in limited supply. Any gene leading to the production of more males (a allele results in more males the A allele at a sex determination locus) will be favored until the frequency of males is >50%. Sex ratios tend to stabilize at 50:50 (R. A. Fisher, 1930)....
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This note was uploaded on 11/05/2011 for the course BIOLOGY MCB2010 taught by Professor Jessicadigirolamo during the Fall '10 term at Broward College.

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