Question 1

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

Accepted Answer

Lethal alleles can cause a distortion in segregation ratios because they can result in the death of organisms that carry them, leading to a missing class of expected progeny.

Question 2

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

Accepted Answer

Complete dominance results in the phenotype of a heterozygote being indistinguishable from that of an organism homozygous for the dominant allele, as the dominant allele masks the effect of the recessive allele in heterozygotes.

Question 3

A man with blood type A (whose mother was blood type O) has children with a woman that has blood type AB. The man and the woman are also heterozygous for the H antigen. What is the probability that they will have a child with blood type A?

Accepted Answer

The man has genotype AO (since his mother was type O), and the woman has genotype AB. The possible blood types for their children are A, B, and AB. The probability of a child having blood type A is 1/2 (from AO x AB) multiplied by the probability of inheriting the H antigen, which is 3/4, resulting in 3/8.

Question 4

In certain goat breeds, appearance of a chin beard is a sex- influenced trait. Recall that bearding is inherited as an autosomal trait determined by two alleles, B1 and B2, and females must be homozygous for the bearded allele, B2, to have a beard. What genotypes must a bearded billy goat (male) and a beardless female goat have if they have a bearded female offspring?

Accepted Answer

For a bearded female offspring to occur, she must inherit a bearded allele (B2) from both parents. Since the female is beardless, she cannot be homozygous for the bearded allele (B2B2) as stated in the question, but must carry one bearded allele to pass to her offspring, making her heterozygous (B1B2). The bearded billy goat can be either heterozygous (B1B2) or homozygous (B2B2) for the bearded allele to pass it on.

Question 5

Which of the following is correct regarding individuals who are blood type AB?

Accepted Answer

Individuals with blood type AB have both A and B antigens on their red blood cells and do not have anti-A or anti-B antibodies, making them universal recipients for blood transfusions.

Question 6

Two proteins interact to form a multimeric complex. When one of the proteins is mutated, there is a substantial loss of functional activity in the multimeric protein. This type of mutation is classified as__________ .

Accepted Answer

Dominant negative mutations occur when a mutant protein interferes with the function of the wild-type protein within the same multimeric complex, leading to a substantial loss of functional activity. This is because the mutant protein can still integrate into the complex but impairs its function, rather than simply reducing the amount of functional protein (as in a null or hypomorphic mutation) or altering the function in a way that increases activity (hypermorphic) or creates a new function (neomorphic).

Question 7

A mutation results in an enzyme that is partially active compared to the wild- type allele. This type of "leaky" mutation is classified as _______.

Accepted Answer

Hypomorphic mutations result in a gene product with reduced activity, hence the term "leaky" mutation, as it allows for some level of function compared to the wild-type allele.

Question 8

Which mode of inheritance produces heterozygotes with phenotypes that differ from either homozygote but typically more closely resembles one homozygous phenotype than the other?

Accepted Answer

Incomplete dominance is the mode of inheritance where the phenotype of the heterozygotes is intermediate between the phenotypes of the two homozygotes, often resembling one homozygous phenotype more closely than the other.

Question 9

The amount of enzyme activity in a cell that is homozygous for a mutant allele is 0 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 0 units. What type of allele is the mutant allele?

Accepted Answer

The mutant allele is dominant negative because it completely suppresses the enzyme activity even in the presence of a wild-type allele, indicating it interferes with the function of the normal protein.

Question 10

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?

Accepted Answer

Sex-influenced traits are those where the phenotype is influenced by the sex of the individual, even if they have the same genotype. In goats, the appearance of a chin beard can be a sex-influenced trait, where the trait is expressed differently in males and females.

Question 11

The parental cross between a rabbit with the Himalayan phenotype (genotype chch) and an albino rabbit (genotype cc) results in F1 rabbits that all have the Himalayan phenotype (genotype chc).  If the resulting F1 rabbits are crossed, what proportion of the F2 offspring will have the Himalayan phenotype and what causes the hypomorphic ch allele to be unstable and result in the distinctive fur pattern?

Accepted Answer

The answer of The parental cross between a rabbit with...

Question 12

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 ________.

Accepted Answer

Hypermorphic mutations result in excessive expression of a protein, which can lead to oncogenesis.

Question 13

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 is the dominance relationship between the WT and mutant allele for the phenotype of amount of enzyme per cell?

Accepted Answer

The heterozygote has an intermediate level of enzyme activity (300 units) compared to either homozygote (400 units for the mutant and 200 units for the WT), indicating incomplete dominance.

Question 14

A mutation resulting in an inactive gene product is classified as _________.

Accepted Answer

Null or amorphic mutations result in a gene product that is either not produced at all or is completely non-functional, effectively acting as if the gene were deleted.

Question 15

You discover a new allele of a gene important for tail formation in mice. WT mice have long tails, but mice heterozygous for the allele have short tails. When you cross two heterozygous mice together, you obtain a 2:1 ratio of short- tailed mice to long- tailed mice. None of the short- tailed progeny are homozygous. What type of allele results in short tails?

Accepted Answer

The 2:1 ratio of short-tailed to long-tailed mice, with no homozygous short-tailed progeny, suggests that the allele causing short tails is lethal when homozygous. This is characteristic of a lethal allele.

Question 16

Brachydactyly type D is human autosomal dominant condition in which the thumbs are abnormally short and broad. In most cases, both thumbs are affected, but occasionally just one thumb is involved. The pedigree above shows a family in which brachydactlyly type D is segregating. Filled circles and squares represent females and males who have involvement of both thumbs. Half- filled in symbols represent family members with just one thumb affected?  There is evidence of variable expressivity and incomplete penetrance in this family. Which individu most likely nonpenetrant for the trait?

Accepted Answer

The answer of Brachydactyly type D is human autosomal dominant...

Question 17

Brachydactyly type D is human autosomal dominant condition in which the thumbs are abnormally short and broad. In most cases, both thumbs are affected, but occasionally just one thumb is involved. The pedigree above shows a family in which brachydactlyly type D is segregating. Filled circles and squares represent females and males who have involvement of both thumbs. Half- filled in symbols represent family members with just one thumb affected?
  There is evidence of variable expressivity and incomplete penetrance in this family. Which individu most likely nonpenetrant for the trait?

Accepted Answer

The answer of Brachydactyly type D is human autosomal dominant...

Question 18

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?

Accepted Answer

Hypermorphic alleles result in an increase in the normal function of the gene product, which is consistent with the observed increase in enzyme activity in cells homozygous for the mutant allele compared to those homozygous for the wild-type allele.

Question 19

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

Accepted Answer

Codominance is the mode of inheritance where both alleles in a heterozygous individual are fully expressed, leading to a phenotype where both traits are detected equally.

Question 20

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__________ .

Accepted Answer

Neomorphic mutations result in a gene product with a new function or that is expressed at a time or place where it is not normally expressed, thus introducing a novel phenotype.

Quiz 4: Inheritance Patterns of Single Genes and Gene Interaction