Heredity Part 2 Concept Review 3

Figure 12.5 A test cross can be performed to determine whether an organism expressing a dominant trait is a

homozygote or a heterozygote.

1

Figure 12.6 Alkaptonuria is a recessive genetic disorder in which two amino acids, phenylalanine and tyrosine,

are not properly metabolized. Affected individuals may have darkened skin and brown urine, and may suffer joint

damage and other complications. In this pedigree, individuals with the disorder are indicated in blue and have the

genotype aa. Unaffected individuals are indicated in yellow and have the genotype AA or Aa. Note that it is often

possible to determine a person’s genotype from the genotype of their offspring. For example, if neither parent has

the disorder but their child does, they must be heterozygous. Two individuals on the pedigree have an unaffected

phenotype but unknown genotype. Because they do not have the disorder, they must have at least one normal

allele, so their genotype gets the “A?” designation.

1

Figure 12.12 Punnett square analysis is used to determine the ratio of offspring from a cross between a red-eyed

male fruit fly and a white-eyed female fruit fly.

1

Figure 12.16 This dihybrid cross of pea plants involves the genes for seed color and texture.

1

The ABO blood groups in humans are expressed as
the IA, IB, and i alleles. The IA allele encodes the A blood
group antigen, IB encodes B, and i encodes O. Both A and
B are dominant to O. If a heterozygous blood type A
parent (IAi) and a heterozygous blood type B parent (IBi)
mate, one quarter of their offspring will have AB blood
type (IAIB) in which both antigens are expressed equally.
Therefore, ABO blood groups are an example of:

a. multiple alleles and incomplete dominance

b. codominance and incomplete dominance

c. incomplete dominance only

d. multiple alleles and codominance

1

In a mating between two individuals that are
heterozygous for a recessive lethal allele that is expressed
in utero, what genotypic ratio (homozygous
dominant:heterozygous:homozygous recessive) would you
expect to observe in the offspring?

a. 1:2:1

b. 3:1:1

c. 1:2:0

d. 0:2:1

1

Assuming no gene linkage, in a dihybrid cross of
AABB x aabb with AaBb F1 heterozygotes, what is the
ratio of the F1 gametes (AB, aB, Ab, ab) that will give rise
to the F2 offspring?

a. 1:1:1:1

b. 1:3:3:1

c. 1:2:2:1

d. 4:3:2:1

1

The forked line and probability methods make use of
what probability rule?

a. test cross

b. product rule

c. monohybrid rule

d. sum rule

1

How many different offspring genotypes are expected
in a trihybrid cross between parents heterozygous for all
three traits when the traits behave in a dominant and
recessive pattern? How many phenotypes?

a. 64 genotypes; 16 phenotypes

b. 16 genotypes; 64 phenotypes

c. 8 genotypes; 27 phenotypes

d. 27 genotypes; 8 phenotypes

1

Heredity Part 2 Concept Review 3

In a mating between two individuals that areheterozygous for a recessive lethal allele that is expressedin utero, what genotypic ratio (homozygousdominant:heterozygous:homozygous recessive) would youexpect to observe in the offspring?

Assuming no gene linkage, in a dihybrid cross ofAABB x aabb with AaBb F1 heterozygotes, what is theratio of the F1 gametes (AB, aB, Ab, ab) that will give riseto the F2 offspring?

The forked line and probability methods make use ofwhat probability rule?

How many different offspring genotypes are expectedin a trihybrid cross between parents heterozygous for allthree traits when the traits behave in a dominant andrecessive pattern? How many phenotypes?

In a mating between two individuals that areheterozygous for a recessive lethal allele that is expressedin utero, what genotypic ratio (homozygousdominant:heterozygous:homozygous recessive) would youexpect to observe in the offspring?

Assuming no gene linkage, in a dihybrid cross ofAABB x aabb with AaBb F1 heterozygotes, what is theratio of the F1 gametes (AB, aB, Ab, ab) that will give riseto the F2 offspring?

The forked line and probability methods make use ofwhat probability rule?

How many different offspring genotypes are expectedin a trihybrid cross between parents heterozygous for allthree traits when the traits behave in a dominant andrecessive pattern? How many phenotypes?

In a mating between two individuals that are
heterozygous for a recessive lethal allele that is expressed
in utero, what genotypic ratio (homozygous
dominant:heterozygous:homozygous recessive) would you
expect to observe in the offspring?

Assuming no gene linkage, in a dihybrid cross of
AABB x aabb with AaBb F1 heterozygotes, what is the
ratio of the F1 gametes (AB, aB, Ab, ab) that will give rise
to the F2 offspring?

The forked line and probability methods make use of
what probability rule?

How many different offspring genotypes are expected
in a trihybrid cross between parents heterozygous for all
three traits when the traits behave in a dominant and
recessive pattern? How many phenotypes?

In a mating between two individuals that are
heterozygous for a recessive lethal allele that is expressed
in utero, what genotypic ratio (homozygous
dominant:heterozygous:homozygous recessive) would you
expect to observe in the offspring?

Assuming no gene linkage, in a dihybrid cross of
AABB x aabb with AaBb F1 heterozygotes, what is the
ratio of the F1 gametes (AB, aB, Ab, ab) that will give rise
to the F2 offspring?

The forked line and probability methods make use of
what probability rule?

How many different offspring genotypes are expected
in a trihybrid cross between parents heterozygous for all
three traits when the traits behave in a dominant and
recessive pattern? How many phenotypes?