Chapter 23 Biology: Evolution of Populations

23.1 If a population stopped reproducing sexually (but still reproduces asexually), how would its genetic variation be affected over time? Explain.

its genetic variation would probably decrease over time. during meiosis, crossing over and the independent assortment of chromosomes produce many new combinations of alleles. in addition, a population contains a vast number of possible mating combinations, and fertilization brings together the gametes of individuals with different genetic backgrounds. thus, via crossing over, independent assortment of chromosomes, and fertilization, sexual reproduction reshuffles alleles into fresh combinations each generation. without sexual reproduction, the rate of forming new combinations of alleles would be vastly reduced, causing the overall amount of genetic variation to drop

23.1 Of all the mutations that occur in a population, why do only a small fraction become widespread?

many mutations occur in somatic cells, which do not produce gametes and so are lost when the organism dies. of mutations that do occur in cell lines that produce gametes, many do not have a phenotypic effect on which natural selection can act. others have a harmful effect and are thus unlikely to increase in frequency because they decrease the reproductive success of their bearers

23-S1 Why do biologists estimate gene variability and nucleotide variability, and what do these estimates represent?

one reason biologists estimate gene variability and nucleotide variability is to assess whether populations have enough genetic variation for evolution to occur. gene variability indicates the extent to which individuals differ genetically at the whole-gene level. nucleotide variability provides a measure of genetic variation at the DNA sequence level

23.2 In Figure 23.8, if the frequency of the Cr allele is 60%, predict the frequencies of the CrCr, CrCw and CwCw genotypes.

the predicted frequencies are 36% CRCR, 48% CRCW, and 16% CWCW