AP Biology Unit 5: Heredity

During meiosis, homologous chromosomes separate from each other during which phase?

Two genes, R and S, are located 20 cM apart on chromosome 3. An individual with genotype RS/rs (in coupling) mates with an rs/rs individual. A student predicts the offspring will show a 1:1 ratio of parental to recombinant phenotypes. Is the student correct, and what is the actual expected ratio of all four phenotypic classes?

In a cross between two individuals who both carry recessive alleles for cystic fibrosis (Cc × Cc), what is the probability that their first three children are ALL unaffected?

In humans, red-green color blindness is an X-linked recessive trait. A color-blind woman and a man with normal color vision have children. What is the expected phenotypic ratio for their sons?

Genomic imprinting results in differential expression of a gene depending on whether it was inherited from the mother or the father. The Igf2 gene in mice is only expressed from the paternal chromosome. If an Igf2 deletion is inherited from the father, the offspring will lack Igf2 expression entirely. What would happen if the same deletion were inherited from the mother?

A plant breeder crosses two true-breeding plants: one with red flowers and one with white flowers. All F₁ plants have pink flowers. When F₁ plants are self-fertilized, the F₂ ratio is 1 red : 2 pink : 1 white. This pattern of inheritance is best explained by which of the following?

A woman is heterozygous for a balanced chromosomal translocation between chromosomes 14 and 21. During meiosis, if the translocated chromosome 21 and the normal chromosome 21 both segregate to the same cell, which of the following describes the result in the offspring if that cell is fertilized by a normal sperm?

In chickens, feather color is controlled by two genes. Allele E (dominant) produces black feathers; allele e (homozygous recessive, ee) produces red feathers when at least one C allele is present. However, any bird homozygous recessive at the C locus (cc) is white regardless of the E locus. This is an example of recessive epistasis. When two white birds both with genotype EEcc are crossed with birds of genotype EECc, what fraction of offspring are expected to be white?

A scientist is studying a gene located on the X chromosome. She crosses a wild-type female (X^+ X^+) with a mutant male (X^m Y). She then crosses the F₁ females with wild-type males. What phenotypic ratio would be expected in F₂ males?

In pea plants, round seed shape (R) is dominant over wrinkled (r), and yellow seed color (Y) is dominant over green (y). Two plants both heterozygous for both traits are crossed. What fraction of the offspring is expected to have round yellow seeds?

A woman with blood type A (genotype I^A i) and a man with blood type B (genotype I^B i) have four children. Based on ABO blood type genetics, which of the following combinations of blood types is possible among their four children?

A researcher is studying two genes, A and B, in fruit flies. When the genes are on the same chromosome, they tend to be inherited together more often than expected under independent assortment. A cross yields 42% AB, 42% ab, 8% Ab, and 8% aB gametes. Which of the following best explains these results?