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Exam 4: Inheritance Patterns of Single Genes and Gene Interaction

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Question 21

Multiple Choice

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Which phenomenon explains differences in the inheritance patterns of the appearance of a chin beard between males and females of certain species of goats, even when their genotypes are the same?

A) sex- limited trait
B) lethal allele
C) sex- influenced trait
D) incomplete penetrance
E) variable expressivity

F) B) and E)
G) C) and E)

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Question 22

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The amount of enzyme activity in a cell that is homozygous for a mutant allele is 400 units. The amount of enzyme activity in a cell homozygous for the WT allele is 200 units. The amount of enzyme activity in a heterozygote is 300 units. What type of allele is the mutant allele?

A) hypermorphic
B) hypomorphic
C) neomorphic
D) null/ amorphic
E) dominant negative

F) B) and D)
G) A) and D)

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Question 23

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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?

What type of allele is often detected as a distortion in segregation ratios, where one class of expected progeny is missing?

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.

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__________ .

Hypermorphic and neomorphic mutations are__________ mutations, which cause overexpression or result in new functions.

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?

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

Explain how the ch (Himalayan) allele and tyrosinase control the Siamese coat- color pattern. What is the underlying reason that certain parts of a Siamese cat (e.g., tail and ears) are darker than the cat's trunk?

The 9:6:1 ratio seen in the dihybrid cross of summer squash indicates what genetic relationship between the two genes controlling fruit shape?

Wild- type bacteria can grow on minimal medium. Four mutants that cannot grow on minimal med but can grow on minimal medium supplemented with the nutrient "H" are isolated. It is suspected t metabolites T, P, and A are in the biochemical pathway for synthesis of H, so each mutant is tested f ability to grow on minimal medium supplemented with these metabolites: A. Mutant 1: can grow on minimal medium supplemented with T, but not P or A B. Mutant 2: is unable to grow on minimal medium supplemented with T, P, or A C. Mutant 3: is able to grow on minimal medium supplemented with A or T, but not P D. Mutant 4: can grow on minimal medium supplemented with T, P, or A. Which of the following is NOT consistent with this information?

To better understand which genes are involved in developmental pathways, geneticists use experimental analyses of mutant phenotypes. What is this analytic approach called?

Two pure- breeding mutant plants produce white flowers. When they are crossed, all of the progeny have wild- type purple flowers. What does this genetic complementation tell you?

People with the dominant mutant polydactyly allele can have extra digits on one or both of their hands. What is the genetic explanation for this observation?

In yeast, there are three gene products required to synthesize the amino acid lysine. You cross two haploid lysine auxotrophs to form a diploid. The diploid fails to grow on plates lacking lysine. Which of the following can you definitively conclude?

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

What are the three categories of loss- of- function mutations?

Amorphic, hypomorphic, and dominant negative mutations are __________mutations, which decrease or eliminate gene activity.

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)?