Ch 9

A testcross is A) a mating between an individual of unknown genotype and an individual homozygous recessive for the trait of interest. B) a mating between an individual of unknown genotype and an individual heterozygous for the trait of interest. C) a mating between an individual of unknown genotype and an individual homozygous dominant for the trait of interest. D) a mating between two individuals heterozygous for the trait of interest. E) a mating between two individuals of unknown genotype.

A) a mating between an individual of unknown genotype and an individual homozygous recessive for the trait of interest.

All the offspring of a cross between a black-eyed mendelien and an orange-eyed mendelien have black eyes. What is the expected phenotypic ratio of a cross between two orange-eyed mendeliens? A) 3 black-eyed:1 orange-eyed B) 0 black-eyed:1 orange-eyed C) 1 black-eyed:3 orange-eyed D) 1 black-eyed:0 orange-eyed E) 1 black-eyed:1 orange-eyed

B) 0 black-eyed:1 orange-eyed

If I cross a tall plant (Tt) with another tall plant (Tt), what is the percentage of offspring that could be short A. 50% B. 25% C. 75% D. 100%

B. 25%

Dr. Smith's parents have normal hearing. However, Dr. Smith has an inherited form of deafness. Deafness is a recessive trait that is associated with the abnormal allele d. The normal allele at this locus, associated with normal hearing, is D. Dr. Smith's parents could have which of the following genotypes? A) DD and dd B) dd and dd C) Dd and Dd D) DD and DD E) Dd and DD

C) Dd and Dd

What type of genetic trait only manifests itself in the absence of the dominant trait it is masked by dominant trait A. Dominant Trait B. Codominance C. Recessive trait D. Sex linked trait

C. Recessive trait

Which of the following statements regarding genotypes and phenotypes is false? A) The genetic makeup of an organism constitutes its genotype. B) An organism with two different alleles for a single trait is said to be heterozygous for that trait. C) Alleles are alternate forms of a gene. D) An allele that is fully expressed is referred to as recessive. E) The expressed physical traits of an organism are called its phenotype.

D) An allele that is fully expressed is referred to as recessive.

Imagine that we mate two black Labrador dogs with normal vision and find that three of the puppies are like the parents, but one puppy is chocolate with normal vision and another is black with PRA (progressive retinal atrophy, a serious disease of vision). We can conclude that A) both of the parents are homozygous for both traits. B) one of the parents is homozygous for both traits. C) the same alleles that control coat color can also cause PRA. D) the alleles for color and vision segregate independently during gamete formation. E) the alleles for color and vision segregate dependently during gamete formation.

D) the alleles for color and vision segregate independently during gamete formation.

The phenotypic ratio resulting from a dihybrid cross showing independent assortment is expected to be A) 1:2:1. B) 3:1. C) 9:1:1:3. D) 3:9:9:1. E) 9:3:3:1.

E) 9:3:3:1.

The alleles of a gene are found at ________ chromosomes. A) the same locus on homologous mitochondrial B) the same locus on heterologous C) different loci on homologous D) different loci on heterologous E) the same locus on homologous

E) the same locus on homologous