Exam 5: Extensions and Modifications of Basic Principles

The very rare Bombay blood phenotype in humans (first discovered in Bombay, India) results in blood type O because of the lack of both the A and B antigens in individuals who are of hh genotype. This genotype results in blood type O regardless of the genotype at the unlinked I locus. If two parents are both of I^A I^B Hh genotype (type AB blood), what is the probability that their first child will also have type blood B?

Leber hereditary optic neuropathy (LHON) is a human disease that exhibits cytoplasmic inheritance. It is characterized by rapid loss of vision in both eyes, resulting from the death of cells in the optic nerve. A teenager loses vision in both eyes and is later diagnosed with LHON. How did this individual MOST likely inherit the mutant DNA responsible for this condition?

A 24-year-old woman with myotonic dystrophy, a genetic disorder caused by a dominant mutant allele, has significant muscle weakness and wasting. She has a 1-year-old son with very poor muscle tone, severe weakness, and significant developmental delay. Her affected 55-year-old father has minor cataracts but no muscle weakness. Which of the following terms BEST describes this situation?

In a certain species of plant, flowers occur in three colors: blue, pink, and white. A pure-breeding pink plant is mated with a pure-breeding white plant. All of the F₁ are blue. When the blue F₁ plants are selfed, the F₂ plants occur in the ratio 9 blue : 3 pink : 4 white. The genotype that produces white is ww. The presence of one W allele allows pink or blue color to occur. The alleles at the hypostatic locus are B (blue) and b (pink). -What is the genotype of the pink parent?

In a certain species of plant, flowers occur in three colors: blue, pink, and white. A pure-breeding pink plant is mated with a pure-breeding white plant. All of the F₁ are blue. When the blue F₁ plants are selfed, the F₂ plants occur in the ratio 9 blue : 3 pink : 4 white. The genotype that produces white is ww. The presence of one W allele allows pink or blue color to occur. The alleles at the hypostatic locus are B (blue) and b (pink). - What is the genotype of the white parent?

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 birds heterozygous for cock feathering are mated. What are the phenotypes of the parents?

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 F₂ offspring of a true-breeding "fabulous" father and a true-breeding "plain" mother (aa bb)?

In a certain species of plant, flowers occur in three colors: blue, pink, and white. A pure-breeding pink plant is mated with a pure-breeding white plant. All of the F₁ are blue. When the blue F₁ plants are selfed, the F₂ plants occur in the ratio 9 blue : 3 pink : 4 white. -How many gene pairs control the flower color phenotype?

List at least four phenomena that can alter expected Mendelian phenotypic ratios in genetic crosses.

The presence of a beard on some goats is determined by an autosomal gene that is dominant in males and recessive in females. Heterozygous males are bearded, while heterozygous females are beardless. What type of inheritance is exhibited by this trait?

How does epistasis differ from Mendel's principle of dominance?

A man is heterozygous for a rare trait that is assumed to be caused by a dominant autosomal mutant allele. He marries a woman who is phenotypically normal. They have a phenotypically normal daughter who marries a phenotypically normal man. Unexpectedly their first child, a girl, has the same abnormal trait as her grandfather. Which of the following BEST explains this situation?

Two loci control body color in beetles. In a cross between a black beetle and a white beetle you obtain a ratio of 9 black to 7 white beetles. What kind of gene interaction is this?