Which individual in Figure 18-3 has the most heterozygous loci, and which individual has the fewest?

Suppose that the seven chromosomes in Figure 18-4a represent a random sample of chromosomes from a population.

Looking at Figure 18-6, can you count how many mitochondrial haplotypes were carried from Asia into the Americas?

In Figure 18-13, the “unrelated” (blue) column for Japan is higher than the “unrelated” column for France. What does this tell you?

In Figure 18-14, some individuals have unique SNP alleles—for example, the T allele at SNP4 occurs only in individual 12. Can you identify two individuals each of whom have unique alleles at two SNPs?

Looking at Figure 18-20, do people of the Middle East tend to have higher or lower levels of heterozygosity compared to the people of East Asia? Why might this be the case?

What are the forces that can change the frequency of an allele in a population?

What assumptions are made when using the Hardy–Weinberg formula to estimate genotypic frequencies from allele frequencies?

In a population of mice, there are two alleles of the A locus (A₁ and A₂). Tests showed that, in this population, there are 384 mice of genotype A₁/A₁, 210 of A₁/A₂, and 260 of A₂/A₂. What are the frequencies of the two alleles in the population?

In a natural population of Drosophila melanogaster, the alcohol dehydrogenase gene has two alleles called F (fast) and S (slow) with frequencies of Adh-F at 0.75 and Adh-S at 0.25. In a sample of 480 flies from this population, how many individuals of each genotypic class would you expect to observe under Hardy–Weinberg equilibrium?

In a randomly mating laboratory population of Drosophila, 4 percent of the flies have black bodies (encoded by the autosomal recessive b), and 96 percent have brown bodies (the wild type, encoded by B). If this population is assumed to be in Hardy–Weinberg equilibrium, what are the allele frequencies of B and b and the genotypic frequencies of B/B and B/b?

In a population of a beetle species, you notice that there is a 3:1 ratio of shiny to dull wing covers. Does this ratio prove that the shiny allele is dominant? (Assume that the two states are caused by two alleles of one gene.) If not, what does it prove? How would you elucidate the situation?

Cystic fibrosis (CF) is an autosomal recessive disorder that occurs relatively frequently among people of European descent. In an Amish community in Ohio, medical researchers reported the occurrence of cystic fibrosis (CF) as being 1/569 live births. Using the Hardy–Weinberg rule, estimate the frequency of carriers of the disease allele in this Amish population.

The relative fitness values of three genotypes are w_A/A = 1.0, w_A/a = 1.0, and w_a/a = 0.7

A/A and A/a individuals are equally fertile. If 0.1 percent of the population is a/a, what selection pressure exists against a/a if the A → a mutation rate is 10⁻⁵? Assume that the frequencies of the alleles are at their equilibrium values.

When alleles at a locus act in a semidominant fashion on fitness, the relative fitness of the heterozygote is midway between the two homozygous classes. For example, genotypes with semidominance at the A locus might have these relative fitnesses: w_A/A = 1.0, w_A/a = 0.9, and w_a/a = 0.8.

If the recessive allele for an X-linked recessive disease in humans has a frequency of 0.02 in the population, what proportion of individuals in the population will have the disease? Assume that the population is 50:50 male:female.

Red-green color blindness is an X-linked recessive disorder in humans caused by mutations in one of the genes that encodes the light-sensitive protein, opsin. If the mutant allele has a frequency of 0.08 in the population, what proportion of females will be carriers? Assume that the population is 50:50 male:female.

Is a new neutral mutation more likely to reach fixation in a large or small population?

It seems clear that inbreeding causes a reduction in fitness. Can you explain why?

In a population of 50,000 diploid individuals, what is the probability that a new neutral mutation will ultimately reach fixation? What is the probability that it will ultimately be lost from the population?

Inbreeding in a population causes a deviation from Hardy–Weinberg expectations such that there are more homozygotes than expected. For a locus with a rare deleterious allele at a frequency of 0.04, what would be the frequency of homozygotes for the deleterious allele in populations with inbreeding coefficients of F = 0.0 and F = 0.125?

Sickle-cell anemia is a recessive autosomal disorder that is caused by an amino acid substitution in the β-hemoglobin protein. The DNA mutation underlying this substitution is a SNP that alters a GAG codon for the amino acid glutamate to a GTG that codes a valine. The frequency of sickle-cell anemia among African Americans is about 1/400. What is the frequency of this GTG codon in the β-hemoglobin gene among African Americans?

You have a sample of 10 DNA sequences of 100 bp in length from a section of highly conserved gene from 10 individuals of a species. The 10 sequences are almost entirely identical; however, each sequence carries one unique SNP not found in any of the others. What is the nucleotide diversity for this sample of sequences?

Figure 18-14 presents haplotype data for the G6PD gene in a worldwide sample of people.

Figure 18-12 shows a pedigree for the offspring of a half-sib mating.

Consider 10 populations that have the genotype frequencies shown in the following table:

The hemoglobin B gene (Hb) has a common allele (A) of a SNP (rs334) that encodes the Hb^A form of (adult) hemoglobin and a rare allele (T) that encodes the sickling form of hemoglobin, Hb^S. Among 571 residents of a village in Nigeria, 440 were A/A and 129 were A/T, and 2 were T/T individuals were observed. Use the χ² test to determine whether these observed genotypic frequencies fit Hardy–Weinberg expectations.

A population has the following gametic frequencies at two loci: AB = 0.4, Ab = 0.1, aB = 0.1, and ab = 0.4. If the population is allowed to mate at random until linkage equilibrium is achieved, what will be the expected frequency of individuals that are heterozygous at both loci?

Two species of palm trees differ by 50 bp in a 5000-bp stretch of DNA that is thought to be neutral. The mutation rate for these species is 2 × 10⁻⁸ substitutions per site per generation. The generation time for these species is five years. Estimate the time since these species had a common ancestor.

Color blindness in humans is caused by an X-linked recessive allele. Ten percent of the males of a large and randomly mating population are color-blind. A representative group of 1000 people from this population migrates to a South Pacific island, where there are already 1000 inhabitants and where 30 percent of the males are color-blind. Assuming that Hardy–Weinberg equilibrium applies throughout (in the two original populations before the migration and in the mixed population immediately after the migration), what fraction of males and females can be expected to be color-blind in the generation immediately after the arrival of the migrants?

Using pedigree diagrams, calculate the inbreeding coefficient (F) for the offspring of (a) parent-offspring matings; (b) first-cousin matings; (c) aunt-nephew or uncle–niece matings; (d) self-fertilization of a hermaphrodite.

A group of 50 men and 50 women establish a colony on a remote island. After 50 generations of random mating, how frequent would a recessive trait be if it were at a frequency of 1/500 back on the mainland? The population remains the same size over the 50 generations, and the trait has no effect on fitness.

Figure 18-22 shows 10 haplotypes from a population before a selective sweep and another 10 haplotypes many generations later after a selective sweep has occurred for this chromosomal region. There are 11 loci defining each haplotype, including one with a red allele that was the target of selection. In the figure, two loci are designated as A and B. These loci each have two alleles: one black and the other gray. Calculate the linkage disequilibrium parameter (D) between A and B, both before and after the selective sweep. What effect has the selective sweep had on the level of linkage disequilibrium?

The recombination rate (r) between linked loci A and B is 0.10. In a population, we observe the following haplo-typic frequencies:

Allele B is a deleterious autosomal dominant. The frequency of affected individuals is 4.0 × 10⁻⁶. The reproductive capacity of these individuals is about 30 percent that of normal individuals. Estimate μ, the rate at which b mutates to its deleterious allele B. Assume that the frequencies of the alleles are at their equilibrium values.

What is the equilibrium heterozygosity for a SNP in a population of 50,000 when the mutation rate is 3 × 10 ⁻⁸?

Of 31 children born of father-daughter matings, 6 died in infancy, 12 were very abnormal and died in childhood, and 13 were normal. From this information, calculate roughly how many recessive lethal genes we have, on average, in our human genomes. (Hint: If the answer were 1, then a daughter would stand a 50 percent chance of carrying the lethal allele, and the probability of the union’s producing a lethal combination would be 1/2 × 1/4 = 1/8. So 1 is not the answer.) Consider also the possibility of undetected fatalities in utero in such matings. How would they affect your result?

The B locus has two alleles B and b with frequencies of 0.95 and 0.05, respectively, in a population in the current generation. The genotypic fitnesses at this locus are w_B/B = 1.0, w_B/b = 1.0, and w_b/b = 0.0

The sd gene causes a lethal disease of infancy in humans when homozygous. One in 100,000 newborns die each year of this disease. The mutation rate from Sd to sd is 2 × 10 ⁻⁴. What must the fitness of the heterozygote be to explain the observed gene frequency in view of the mutation rate? Assign a relative fitness of 1.0 to Sd/Sd homozygotes. Assume that the population is at equilibrium with respect to the frequency of sd.

If we define the total selection cost to a population of deleterious recessive genes as the loss of fitness per individual affected (s) multiplied by the frequency of affected individuals (q²), then selection cost = sq².

Balancing selection acts to maintain genetic diversity at a locus since the heterozygous class has a greater fitness than the homozygous classes. Under this form of selection, the allele frequencies in the population approach an equilibrium point somewhere between 0 and 1. Consider a locus with two alleles A and a with frequencies p and q, respectively. The relative genotypic fitnesses are shown below, where s and g are the selective disadvantages of the two homozygous classes.