Quiz 6 Genetics

Among sibships consisting of five children and assuming a sex ratio of 1:1, what is the proportion with no boys?

(1/2)^5

In the cross Aa Bb Cc Dd × Aa Bb Cc Dd, in which all genes undergo independent assortment, what proportion of offspring are expected to be homozygous recessive for all four genes?

(1/4)^1/4

Assuming equal sex ratios, if a mating has already produced three girls, what is the probability that the next child will be a girl?

1/2

Starting with a P1 cross between AA and aa, the proportion of heterozygotes in the F2 progeny will be

1/2

A woman with keratosis, a skin condition caused by a rare dominant allele, marries a normal man, and they have two children. What is the probability that both children are normal?

1/4

In families where both parents are heterozygous for a recessive trait, what is the probability of their having a child with the homozygous recessive genotype?

1/4

Assuming independent assortment, how many different gametes can be formed by an organism that is homozygous for three and heterozygous for two genes?

4

Mating of two organisms produces a 3:1 ratio of phenotypes in the progeny. The parental genotypes are

Aa x Aa

Mating of two organisms produces a 1:1 ratio of phenotypes in the progeny. The parental genotypes are

Aa x aa

In the formation of gametes, a pair of homologous genes will wind up such that each gamete contains only one homologous copy of each gene. This is a paraphrasing of...

Mendel's Law of Segregation

You have a plant derived from a round, yellow pea and want to know its genotype. You testcross this plant and find 50% of the peas are round, yellow and 50% are round, green. What is the genotype of the parent plant? W=round w=wrinkled G=yellow g=green

WWGg

Probabilities are calculated using the multiplication rule when they

are independent

Probabilities are calculated using the addition rule when they

are mutually exclusive

Parents heterozygous for a recessive allele are called

carriers

Diametrical traits that have two mutually exclusive versions with no intermediate phenotype, such as wrinkled vs. smooth peas, are often..

controlled by a single gene

The interaction between nonallelic genes in their effects on a trait is called _____. This often results in one gene masking the expression of the other.

epistasis

The situation in which an expected phenotype is not expressed is referred to as

incomplete penetrance

In dihybrid crosses, the ratio 9:3:3:1 indicates

independent assortment

Mating an individual of dominant phenotype, unknown genotype with a recessive homozygote is called _____.

testcross