Exam 4: Gene Interaction

You have crossed two Mexican hairless dogs, and the offspring are 1/3 hairy and 2/3 hairless. Given this phenotypic ratio, draw the Punnett square for this cross. What are the genotypes of the P₁ and F₁ dogs in this cross? List the predicted genotype as well as the phenotype for each of the offspring. Which genotypes are hairless, and which are hairy? Can you design a genetic cross that would yield a true-breeding hairless line (where all offspring are hairless)?

Are loss-of-function mutations more likely to be dominant or recessive?

Which step is catalyzed by the enzyme responsible for the Met 3 mutant?

Bateson and Punnett crossed two white-flowered lines and saw all purple flowers in the F₁ generation. They concluded this was an example of complementary gene interactions because a cross of the F₁ plants yielded what ratio in the F₂ generation?

Phenylketonuria (PKU)is caused by the absence of the enzyme phenylalanine hydroxylase, which catalyzes the first step of the pathway that breaks down the amino acid phenylalanine, a common component of dietary protein. Explain how environmental intervention is commonly practiced to prevent the development of this human autosomal recessive condition.

Independent assortment predicts a 9:3:3:1 ratio with four different phenotypes in the F₂ progeny. If the alleles are epistatic, what would you predict?

A mutation results in a gene product with a novel function that is not normally found in wild-type organisms. This type of mutation is known as __________.

Many oncogenes result from mutations that cause a protein to be expressed in cells where it is normally not expressed or is expressed at inappropriate times during development. This type of mutation can be described as __________.

________ mutations cause overexpression or result in new functions.

Most combinations of different ABO alleles result in complete dominance of one allele. Which combination results in codominance?

If a dominant allele of one gene completely suppresses the phenotypic expression of alleles of another gene, this is an example of __________.

In Labrador retrievers, coat color is controlled by gene interaction in which homozygosity for a recessive allele can mask the phenotypic expression of a second gene. This genetic interaction is known as ________ and has a characteristic ________ ratio.

You cross a pure-breeding white flower with a pure-breeding red flower, and the offspring are white with red spots. This is an example of what type of inheritance?

Which antigen, expressed on the surface of all red blood cells, is modified by A- or B-transferases?

________ mutations decrease or eliminate gene activity.

Which mode of inheritance results in both alleles being detected equally in the heterozygous phenotype?

Which mode of inheritance results in the phenotype of a heterozygote being indistinguishable from that of an organism homozygous for the dominant allele?

The allele responsible for the Siamese coat-color pattern produces an unstable tyrosinase enzyme. This type of gene product is an example of what type of allele?

In the biosynthetic pathway for conversion from homoserine to methionine, you identify a Neurospora crassa double mutant Met1/Met2. This mutant will grow only if which supplement(s)are added to the minimal media?

Describe the difference between incomplete penetrance and variable expressivity. It is often difficult to pinpoint the cause of incomplete penetrance or variable expressivity. What possible interactions may be responsible?