Exam 5: Extensions and Modifications of Basic Principles

Huntington's disease tends to strike earlier and lead to a more rapid progression of symptoms as it moves from generation to generation. Also, it tends to strike earlier and progress more rapidly when it is passed from the father to his children rather than from the mother. Which genetic phenomenon (or phenomena) is/are likely operating here? (Select all that apply.)

Suppose that extra fingers and toes are caused by a recessive trait, but it appears in only 60% of homozygous recessive individuals. Two heterozygotes conceive a child. What is the probability that this child will have extra fingers and toes?

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^ch × Cc^h.

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 c^chc^h × c^hc.

Cloning is a procedure by which exact genetic duplicates are made. Using cloning techniques, you have produced 10 cloned cows. However, the fur color of each of the calves looks very different from one another. Explain why this might have occurred.

A mother with blood type A has a child with blood type A. Give all possible blood types for the father of this child.

In the yawncat (a rare hypothetical animal), the dominant allele R causes solid tail color, and the recessive allele r results in white spots on a colored background. The black coat color allele B is dominant to the brown allele b, but the B and b alleles can only be expressed if the animal has an mm genotype at a third gene locus. Animals that are M_ are yellow regardless of which allele from the B locus is present. A mating between a solid yellow-tailed male yawncat and a solid brown-tailed female yawncat produces 16 offspring with the following tail phenotypes: six solid yellow, two spotted yellow, three solid black, one spotted black, three solid brown, and one spotted brown. - What is the MOST likely genotype of the male parent?

The cross of CcDd × CcDd results in a 12:3:1 phenotypic ratio. What is the expected phenotypic ratio when a CcDd × ccdd testcross is made involving the same two genes? (They are assorting independently.)

The phenomenon in which a gene's expression is determined by its parental origin is called:

Interactions among the human ABO blood group alleles involve _____ and _____.

Suppose that the "fabulous" phenotype is controlled by two genes, A and B, as shown in the following diagram. Allele A produces enough enzyme 1 to convert "plain" to "smashing." Allele a produces no enzyme 1. Allele B produces enough enzyme 2 to convert "smashing" to "fabulous." Allele b produces no enzyme 2. The A and B genes are both autosomal and assort independently. - What will be the phenotype(s) of the F₁ offspring of a true-breeding "fabulous" father and a true-breeding "plain" mother (aa bb)?

Coat color is determined by two loci, A and B, 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 is the genotype of the black progeny?

Deafness is often inherited in humans as an autosomal recessive trait. Assume that this is the case here. Two severely deaf people meet and marry. They have four children and all of them have normal hearing. What is the MOST reasonable explanation for this outcome?

In the yawncat (a rare hypothetical animal), the dominant allele R causes solid tail color, and the recessive allele r results in white spots on a colored background. The black coat color allele B is dominant to the brown allele b, but the B and b alleles can only be expressed if the animal has an mm genotype at a third gene locus. Animals that are M_ are yellow regardless of which allele from the B locus is present. A mating between a solid yellow-tailed male yawncat and a solid brown-tailed female yawncat produces 16 offspring with the following tail phenotypes: six solid yellow, two spotted yellow, three solid black, one spotted black, three solid brown, and one spotted brown. - What is the probability of the next offspring from these same two parents having a spotted brown tail?

The red kernel color in wheat is caused by the presence of at least one dominant allele in each of two independently segregating gene pairs (e.g., R_B_). Wheat plants with rrbb genotypes have white kernels, and plants with genotypes R_bb and rrB_ have yellow kernels. You cross a plant homozygous for red kernels (RR BB) with a plant homozygous for white kernels. What are the relative proportions of the phenotypic classes expected in the F₂ progeny after selfing the F₁ progeny?

Male-limited precocious puberty results from a rare autosomal allele (P) that is dominant over the allele for normal puberty (p) and is expressed only in males. A male and female that both went through normal puberty have two sons. The first son undergoes precocious puberty but the second undergoes normal puberty. -What is the genotype of the father?

Describe the differences between dominance, codominance, and incomplete dominance.

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 long-ossicone phenotype? Assume the penetrance of L applies equally to both homozygotes and heterozygotes.

A deletion of a small region on the long arm of chromosome 15 causes a developmental disorder in children called Prader-Willi syndrome when the deletion is inherited from the father. However, the deletion of this same region of chromosome 15 can also be inherited from the mother, but this inheritance results in a completely different set of symptoms, called Angelman syndrome. What type of genetic phenomenon does this represent?

Hair color is determined in Labrador retrievers by alleles at the B and E loci. A dominant allele B encodes black pigment, whereas a recessive allele b encodes brown pigment. Alleles at a second locus affect the deposition of the pigment in the shaft of the hair; dominant allele E allows dark pigment (black or brown) to be deposited, whereas recessive allele e prevents the deposition of dark pigment, causing the hair to be yellow. -What type of gene interaction does this represent?