Inheritance (College Board AP® Biology)

In a certain species of plant, the diploid number of chromosomes is 4 (2n = 4). Flower color is controlled by a single gene in which the green allele (G) is dominant to the purple allele (g). Plant height is controlled by a different gene in which the dwarf allele (D) is dominant to the tall allele (d). Individuals of the parental (P) generation with the genotypes GGDD and ggdd were crossed to produce F₁ progeny.

Construct a diagram below to depict the four possible normal products of meiosis that would be produced by the F₁ progeny. Show the chromosomes and the allele(s) they carry. Assume the genes are located on different chromosomes and the gene for flower color is on chromosome 1.

Predict the possible phenotypes and their ratios in the offspring of a testcross between an F₁ individual and a ggdd individual.

If the two genes were genetically linked, describe how the proportions of phenotypes of the resulting offspring would most likely differ from those of the testcross between an F₁ individual and a ggdd individual.

In the tongue sole fish (Cynoglossus semilaevis), sex is determined by a combination of genetics and environmental temperature. Genetically male fish have two Z chromosomes (ZZ), and genetically female fish have one Z chromosome and one W chromosome (ZW). When fish are raised at 22^oC, ZZ fish develop into phenotypic males and ZW fish develop into phenotypic females. However, when fish are raised at 28^oC, the Z chromosome is modified (denoted as Z*). Z* W individuals develop as phenotypic males that are fertile and can pass on the Z* chromosome to their offspring even when the offspring are raised at 22^oC. A cross between a ZW female and a Z*Z male is shown in the Punnett square below.

Predict the percent of phenotypic males among the F₁ offspring of the cross shown in the Punnett square if the offspring are raised at 22^oC

At least one Z or Z* chromosome is necessary for survival of the fish. A researcher crossed two fish and observed  a 2: 1 ratio of males to females among the offspring. Based on the information, identify the genotype the male parent in the cross. Describe ONE fitness cost to the female of mating with this particular male.

PDC deficiency is caused by mutations in the PDHA 1 gene, which is located on the X chromosome. A male with PDC deficiency and a homozygous female with no family history of PDC deficiency have a male offspring. Calculate the probability that the male offspring will have PDC deficiency.

Geneticists investigated the mode of inheritance of a rare disorder that alters glucose metabolism and first shows symptoms in adulthood. The geneticists studied a family in which some individuals of generations II and Ill are known to have the disorder. Based on the pedigree (Figure 1), the geneticists concluded that the disorder arose in individual II—2 and was caused by a mutation in mitochondrial DNA.

Figure 1. Pedigree of a family showing individuals with the glucose metabolism disorder. A question mark indicates that the phenotype is unknown

TABLE 1. AVERAGE BLOOD GLUCOSE LEVELS OF INDIVIDUALS IN GENERATION IV

TABLE 2. PHENOTYPIC CLASSIFICATIONS BASED ON BLOOD GLUCOSE LEVELS

The disorder alters glucose metabolism. Describe the atoms AND types of bonds in a glucose molecule.

Using the template in the space provided for your response, construct an appropriately labeled graph based on the data in Table 1. Determine one individual who is both at risk of developing the disorder and has a significantly different blood glucose level from that of individual IV — 1.

Based on the pedigree, identify all individuals in generation IV who can pass on the mutation to their children.

Based on the fact that individual II — 2 is affected, a student claims that the disorder is inherited in an X-Iinked recessive pattern. Based on the student's claim, predict which individuals of generation Ill will be affected by the disorder. Based on the pedigree, justify why the data do NOT support the student's claim.