Chapter 18

In four o'clock plants, two alleles (R, r) produce three petal colors. RR plants have red petals, rr plants have white petals, and heterozygotes have pink petals. In a particular population of four o'clocks there are 40 plants with red petals, 50 plants with pink petals, and 10 plants with white petals. What is the frequency of the r allele in this population?

.350

A given autosomal locus has three possible alleles (A1, A2, and A3). Assuming that the numbers of individuals with the six possible genotypes are as follows, what would be the frequency of the A1 allele in the population? A1A1 = 30 A1A2 = 27 A2A2 = 12 A1A3 = 17 A2A3 = 10 A3A3 = 4

0.3

If the frequency of the A allele is 0.7 and the frequency a allele is 0.3 in a given population, what would the frequency be of Aa individuals in the population? (Assume the gene is autosomal with only two possible alleles and the population is in Hardy-Weinberg equilibrium.)

0.42

Sickle-cell anemia is a recessive disease that afflicts approximately 1 in 12 African Americans, meaning that the frequency of ss homozygotes is 0.09. Assuming the African American population is in Hardy-Weinberg equilibrium, what is the frequency of Ss carriers in this population?

2pq = 2(0.7)(0.3) = 0.42

Which of the following is necessary for a new species to arise?

Cladogenesis & Genetic variation

Which of the following prezygotic reproductive isolating mechanisms best explains why salamanders that live in trees do not successfully mate with salamanders that live in soil by rivers?

Ecological isolation

_____ are sets of genes that are similar in sequence but encode different products.

Gene Families

Which of the following evolutionary forces would be expected to increase genetic divergence between two populations of a species?

Mutation & Genetic drift

Most forms of natural selection are directional in that one allele is favored over the other and is eventually fixed in the population. Which form of natural selection allows both alleles to be maintained?

Overdominance

A single population becomes separated by a geographic barrier, and each population acquires genetic differences. Which of the following could happen if this barrier is removed and the two populations interact and attempt to mate?

Reproductive isolating mechanisms may not have evolved and thus the two species could successfully mate. & Prezygotic isolating mechanisms may have evolved, thus preventing the two populations from mating. & Postzygotic isolating mechanisms may have evolved, thus preventing the two populations from producing viable or fertile offspring.

Which of the following statements is true of different species?

Species' differences are easy to recognize in many cases. & Species are different kinds or types of living organisms. & Sometimes different species are so similar in appearance that one must examine their proteins or genes to determine that they are different species.

Which of the following statements is an assumption of the Hardy-Weinberg law?

The population mates randomly.

Three populations of crickets look very similar, but the males have courtship songs that sound different. What function would this difference in song likely serve if the populations came in contact?

a behavioral reproductive isolating mechanism

An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?

a genetic bottleneck

The phenomenon of fusion is likely to occur when, after a period of geographic isolation, two populations meet again and ________.

an increasing number of viable, fertile hybrids is produced over the course of the next 100 generations

Genetic drift produces variation for evolution when ________

chance events cause allele frequencies to fluctuate unpredictably

Migration can _____.

decrease genetic differences between two populations & increase the variation within a population that receives migrants

In underdominance, the HIGHEST fitness is found in which genotype?

dominant homozygous recessive

A population that is in Hardy-Weinberg equilibrium will _____.

have stable allelic frequencies for a locus from one generation to the next & have stable genotypic frequencies for a locus after a single generation of random mating

The _____ approach to inferring relationships among species selects the phylogeny that minimizes the number of evolutionary changes or steps.

parsimony

Gene pools can be described in terms of _____.

phenotypic frequencies & genotypic frequencies

The first step in allopatric speciation is _____.

splitting of a population into two or more groups by a geographic barrier

Rates of synonymous nucleotide substitutions are higher than rates of nonsynonymous nucleotide substitutions because _____.

synonymous mutations have little or no effect on fitness & synonymous substitutions do not change the amino acid sequence, whereas nonsynonymous substitutions do change the amino acid sequence

Soon after the island of Hawaii rose above the sea surface (somewhat less than one million years ago), the evolution of life on this new island should have been most strongly influenced by ________.

the founder effect

Which region of a gene should have the HIGHEST rates of substitution?

third position of a codon