Heredity Part 2 Concept Review 3
by John Lundy
| 11 Questions
Note from the author:
An assignment to reinforce key concept concerning Heredity.
Figure 12.5 A test cross can be performed to determine whether an organism expressing a dominant trait is a
homozygote or a heterozygote.
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.
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.
Figure 12.16 This dihybrid cross of pea plants involves the genes for seed color and texture.
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
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
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
The forked line and probability methods make use of
what probability rule?
a. test cross
b. product rule
c. monohybrid rule
d. sum 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?
a. 64 genotypes; 16 phenotypes
b. 16 genotypes; 64 phenotypes
c. 8 genotypes; 27 phenotypes
d. 27 genotypes; 8 phenotypes
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