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key_sex_worksheet - BIS 2A Quiz#9 March 4 2008 Small-group...

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BIS 2A Quiz #9 March 4, 2008 Small-group activity Name: __________________________________ Section: ________ 1. Alleles are forms of a gene distributed among individuals of a sexual population. Consider the sexual species below , a single-celled organism called Aerobus heterotrophus . Three genes are indicated on chromosomes below: A, B and K. All encode proteins; A and B proteins are essential for viability (survival); K protein is not. (a) Is this organism likely to belong to the domain Eukarya, Archaea, or Bacteria? Briefly, how do you know? (b) A. heterotrophus has a population of 10 individuals, each genetically unique. Shown below are schematics of these individuals, with their genotypes at three loci. 1- Briefly, what is a locus (plural loci) in this context? 2-How many different genes are represented here? 3-How many different alleles are represented here? 4-Is this organism haploid or diploid ? How do you know? 5-Consider Gene A. What is the frequency of allele A9 in the population? Consider Gene B. What is the frequency of allele B1 in the population? Which gene, A, B, or K, has fewest alleles ? Name TWO possible explanations for why there are so few alleles of B. Which explanation is more likely , based on the allele variations you see for genes A and K? B1 K5 A9 B1 K5 A4 B1 K4 A9 B1 K3 A9 B2 K5 A9 B1 K1 A1 B1 K3 A3 B2 K3 A8 B1 K4 A8 B2 K5 A6 B1 K5 A9 B1 K1 A9 B1 K3 A5 B2 K1 A4 B1 K4 A9 B1 K5 A5 B1 K5 A1 B1 K2 A9 B2 K5 A6 B1 K5 A7 1 2 3 4 5 6 7 8 9 10 Eukarya. We know this because it is capable of undergoing sex -- a eukaryotic recombination and assortment specialty. Not all eukaryotes spend their lives as diploids, but certainly diploidy here might also suggest this is eukaryotic. A locus is a position on a chromosome where you find a particular gene. 3 -- A, B, and K. 5 for K (K1-K5) Diploid -- there are two copies of each gene. There are 20 copies of gene A in this population. 8 are allele A9. 8/20 = 0.4 15/20 = 0.75 I didn’t mean to be tricky to leave out allele A2; just overlooked it. Or maybe it’s a dominant lethal allele. B has only 2 alleles in the population. (1) Natural selection. There is strong selection against changes in gene B (most changes reduce fitness and the carriers are eliminated from the gene pool) (2) Genetic drift. For this scenario, a recent chance event in a small population may have caused a ‘bottleneck’, where only a few individuals contributed their alleles to continued generations. Probably natural selection. If it had been a bottleneck event, you’d expect low variation (few alleles) at all gene positions, since all genes will have come from a small number of individuals in recent time. The variability in A and K suggest that there is unusually strong selection against changes in B.
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(Still referring to the A. heterotrophus population above). Imagine that
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key_sex_worksheet - BIS 2A Quiz#9 March 4 2008 Small-group...

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