Exam 5: Extensions and Modifications of Basic Principles

In domestic chickens, some males display a plumage pattern called cock feathering. Other males and all females display a pattern called hen feathering. Cock feathering is an autosomal recessive trait that is exhibited in males only. - Two heterozygous birds are mated. What fraction of the total offspring is expected to exhibit cock feathering?

The himalayan allele in rabbits produces dark fur at the extremities of the body-on the nose, ears, and feet. The dark pigment develops, however, only when a rabbit is reared at a temperature of 25°C or lower; if a Himalayan rabbit is reared at 30°C, no dark patches develop. What does this exemplify?

A mother of blood type A gives birth to a child with blood type O. Which of the following could NOT be the blood type of the father?

Multifactorial traits are influenced by _____ and _____.

Crossing two yellow mice results in 2/3 yellow offspring and 1/3 nonyellow offspring. What percentage of offspring would you expect to be nonyellow if you crossed two nonyellow mice?

You observe continuous variation in tail length in a wild population of rats. How would you determine whether this variation is an example of variable expressivity or polygenic inheritance?

What is a dominant epistatic gene?

Coat color is determined by two loci in large cats. Two pink panthers fall in love and produce a large litter of baby panthers with the following phenotypic ratios: 12/16 pink; 3/16 black; and 1/16 white. -What kind of gene interaction is this?

In rabbits, an allelic series helps to determine coat color: C (full color), c^ch (chinchilla; gray color), c^h (Himalayan; white with black extremities), and c (albino; all white). The C allele is dominant to all others, c^ch is dominant to c^h and c, c^h is dominant to c, and c is recessive to all the other alleles. This dominance hierarchy can be summarized as C > c^ch > c^h > c. -Indicate the phenotypic ratios expected of rabbits with the cross Cc × c^hc.

The bicoid mutation (bcd^-) in fruit flies is inherited as a maternal effect recessive allele. What is the expected ratio of phenotypes in the offspring of a cross between a bcd⁺/bcd^- female and a bcd⁺/bcd^- male?

Assume that a human gene is imprinted. Normal individuals have one active copy of the gene, the copy inherited from their fathers. The copy inherited from their mothers is normally inactive. In one large family a mutation in this gene occurs and this mutation results in part of the gene being deleted. The defective gene is never active regardless of the parent from which it is inherited. Individuals who carry the mutation are heterozygous and also have a normal copy of the gene whose activity depends upon which parent it was inherited from. Individuals who have no active copy of the gene have several medical problems but live long enough to have children of their own. This family includes two phenotypically normal parents who have two affected children, a son and a daughter. Which parent, father or mother, did the affected children inherit this mutation from? Why?

In domestic chickens, some males display a plumage pattern called cock feathering. Other males and all females display a pattern called hen feathering. Cock feathering is an autosomal recessive trait that is exhibited in males only. - Two heterozygous birds are mated. What fraction of the female offspring is expected to exhibit cock feathering?

In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. - Give genotypes for comb shape of the parents in the following cross: Rose crossed with single produces 10 rose and 11 single offspring.

In the endangered African watchamakallit, the offspring of a true-breeding black parent and a true-breeding white parent are all gray. When the gray offspring are crossed among themselves, their offspring occur in a ratio of 1 black : 2 gray : 1 white. Upon close examination of the coats, each hair of a gray animal is gray. What is the mode of inheritance?

Polydactyly is the condition of having extra fingers or toes. Some polydactylous persons possess extra fingers or toes that are fully functional, whereas others possess only a small tag of extra skin. This is an example of:

You are studying a gene that controls ossicone (horn) length in giraffes. The wild-type long-ossicone allele (L) is dominant to the mutant short-ossicone (l) allele. However, the L allele is only 60% penetrant. You cross two heterozygous giraffes. What proportion of offspring would you expect to exhibit the short-ossicone phenotype? Assume the penetrance of L applies equally to both homozygotes and heterozygotes.

Explain the differences between incomplete dominance and continuous variation.

In humans, blood types A and B are codominant to each other and each is dominant to O. What blood types are possible among the offspring of a couple of blood types AB and A?

In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. -Give genotypes for comb shape of the parents in the following cross: Rose crossed with walnut produces 6 walnut, 6 rose, 2 single, and 2 pea offspring.

Two mice of the same species have different ear shapes. You find that one mouse, having ears of normal shape, was caught in a field in Kenya. The other mouse, with curled ears, was caught in the frozen tundra of Greenland. You have determined that both mice have identical genotypes at the gene loci controlling ear shape. How would you explain the differences in ear shape?