The Evolution of Population

The frequency of allele a is 0.45 for a population in Hardy-Weinberg equilibrium. What are the expected frequencies of genotypes AA, Aa, and aa?

A locus that affects susceptibility to a degenerative brain disease has two alleles, V and v. In a population, 16 people have genotype VV, 92 have genotype Vv, and 12 have genotype vv. Is this population evolving? Explain.

Use the observed genotype frequencies from the day 7 data to calculate the frequencies of the CG allele (p) and the CY allele (q).

Next, use the Hardy-Weinberg equation (p2 + 2pq + q2 = 1) to calculate the day seven expected frequencies of genotypes CGCG, CGCY, and CYCY for a population in Hardy-Weinberg equilibrium.

Calculate the observed frequencies of genotypes CGCG, CGCY, and CYCY at day 7. Compare these frequencies to the expected frequencies calculated in question 2. Is the seedling population in Hardy-Weinberg equilibrium at day 7, or is evolution occurring? Explain your reasoning and identify which genotypes, if any, appear to be selected for or against.

Calculate the observed frequencies of genotypes CGCG, CGCY, and CYCY at day 21. Compare these frequencies to the expected frequencies calculated in question 2 and to the observed frequencies at day 7. Is the seedling population in Hardy-Weinberg equilibrium at day 21, or is evolution occurring? Explain your reasoning and identify which genotypes, if any, appear to be selected for or against.

Natural selection changes allele frequencies because some _________ survive and reproduce better than others. 

(A) alleles 

(B) loci 

(C) species 

(D) individuals

Explain why genetic variation within a population is a prerequisite for evolution?

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

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

A population has 700 individuals, 85 of genotype AA, 320 of genotype Aa, and 295 of genotype aa. What are the frequencies of alleles A and a?

Homozygous CYCY individuals cannot produce chlorophyll. The ability to photosynthesize becomes more critical as seedlings age and begin to exhaust the supply of food that was stored in the seed from which they emerged. Develop a hypothesis that explains the data for days 7 and 21. Based on this hypothesis, predict how the frequencies of the CG and CY alleles will change beyond day 21?

In what sense is natural selection more “predictable” than genetic drift?

Distinguish genetic drift from gene flow in terms of (a) how they occur and (b) their implications for future genetic variation in a population. 

Suppose two plant populations exchange pollen and seeds. In one population, individuals of genotype AA are most common (9,000 AA, 900 Aa, 100 aa), while the opposite is true in the other population (100 AA, 900 Aa, 9,000 aa). If neither allele has a selective advantage, what will happen over time to the allele and genotype frequencies of these populations?

What is the relative fitness of a sterile mule? Explain.

Explain why natural selection is the only evolutionary mechanism that consistently leads to adaptive evolution in a population.

Consider a population in which heterozygotes at a certain locus have an extreme phenotype (such as being larger than homozygotes) that confers a selective advantage. Compare this description to the models of selection modes shown in Figure 23.13. Does this situation represent directional, disruptive, or stabilizing selection? Explain your answer.

No two people are genetically identical, except for identical twins. The main source of genetic variation among humans is 

1. new mutations that occurred in the preceding generation. 

2. genetic drift. 

3. the reshuffling of alleles in sexual reproduction. 

4. environmental effects.

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus?

(A) gene variability = 0%; number of alleles = 0

(B) gene variability = 0%; number of alleles = 1

(C) gene variability = 0%; number of alleles = 2

(D) gene variability 7 0%; number of alleles = 2

There are 25 individuals in population 1, all with genotype AA, and there are 40 individuals in population 2, all with genotype aa. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation most likely resulted from

(A) genetic drift.

(B) gene flow.

(C) nonrandom mating.

(D) directional selection.

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?

(A) 0.7 

(B) 0.49 

(C) 0.42 

(D) 0.21

Using at least two examples, explain how the process of evolution is revealed by the imperfections of living organisms.

Researchers studied genetic variation in the marine mussel Mytilus edulis around Long Island, New York. They measured the frequency of a particular allele (lap 94) for an enzyme involved in regulating the mussel’s internal saltwater balance. The researchers presented their data as a series of pie charts linked to sampling sites within Long Island Sound, where the salinity is highly variable, and along the coast of the open ocean, where salinity is constant. (a) Create a data table for the 11 sampling sites by estimating the frequency of lap 94 from the pie charts. (Hint: Think of each pie chart as a clock face to help you estimate the proportion of the shaded area.) (b) Graph the frequencies for sites 1–8 to show how the frequency of this allele changes with increasing salinity in Long Island Sound (from southwest to northeast). Evaluate how the data from sites 9–11 compared with the data from the sites within the Sound. (c) Considering the various mechanisms that can alter allele frequency, construct a hypothesis that explains the patterns you observe in the data and that accounts for the following observations: (1) The lap94 allele helps mussels maintain osmotic balance in water with a high salt concentration but is costly to use in less salty water; and (2) mussels produce larvae that can disperse long distances before they settle on rocks and grow into adults.

Heterozygotes at the sickle-cell locus produce both normal and abnormal (sickle-cell) hemoglobin (see Concept 14.4). When hemoglobin molecules are packed into a heterozygote's red blood cells, some cells receive relatively large quantities of abnormal hemoglobin, making these cells prone to sickling. In a short essay (approximately 100–150 words), explain how these molecular and cellular events lead to emergent properties at biological organization's individual and population levels.

This kettle lake formed 14,000 years ago when a glacier that covered the surrounding area melted. Initially devoid of animal life, over time, the lake was colonized by invertebrates and other animals. Hypothesize how mutation, natural selection, genetic drift, and gene flow may have affected populations that colonized the lake.