Question 1

In domestic chickens, some males display a plumage pattern called cock feathering. Other males and all females display a pattern called hen feathering. Cock feathering is an autosomal recessive trait that is exhibited in males only.
- Two heterozygous birds are mated. What fraction of the total offspring is expected to exhibit cock feathering?

Accepted Answer

A)  0 
B)  1/8 
C)  1/4 
D)  1/2 
E)  3/4

Question 2

The himalayan allele in rabbits produces dark fur at the extremities of the body-on the nose, ears, and feet. The dark pigment develops, however, only when a rabbit is reared at a temperature of 25°C or lower; if a Himalayan rabbit is reared at 30°C, no dark patches develop. What does this exemplify?

Accepted Answer

A)  dominance 
B)  discontinuous characteristic 
C)  genetic imprinting 
D)  phenocopy 
E)  temperature-sensitive allele

Question 3

A mother of blood type A gives birth to a child with blood type O. Which of the following could NOT be the blood type of the father?

Accepted Answer

A)  A 
B)  B 
C)  O 
D)  AB 
E)  Any of these is a possible blood type of the father.

Question 4

Multifactorial traits are influenced by _____ and _____.

Accepted Answer

A)  dominance; codominance 
B)  epistasis; pleiotropy 
C)  age; sex 
D)  genetic imprinting; reduced penetrance 
E)  multiple genes; environment

Question 5

Crossing two yellow mice results in 2/3 yellow offspring and 1/3 nonyellow offspring. What percentage of offspring would you expect to be nonyellow if you crossed two nonyellow mice?

Accepted Answer

A)  25% 
B)  33% 
C)  66% 
D)  75% 
E)  100%

Question 6

You observe continuous variation in tail length in a wild population of rats. How would you determine whether this variation is an example of variable expressivity or polygenic inheritance?

Accepted Answer

The answer of You observe continuous variation in tail length...

Question 7

What is a dominant epistatic gene?

Accepted Answer

The answer of What is a dominant epistatic gene?...

Question 8

Coat color is determined by two loci in large cats. Two pink panthers fall in love and produce a large litter of baby panthers with the following phenotypic ratios: 12/16 pink; 3/16 black; and 1/16 white. 
-What kind of gene interaction is this?

Accepted Answer

A)  recessive epistasis 
B)  dominant epistasis 
C)  duplicate recessive epistasis 
D)  duplicate dominant epistasis 
E)  dominant and recessive epistasis

Question 9

In rabbits, an allelic series helps to determine coat color: C (full color), cS1U1P1chS1S1P0 (chinchilla; gray color), cS1U1P1hS1S1P0 (Himalayan; white with black extremities), and c (albino; all white). The C allele is dominant to all others, cS1U1P1chS1S1P0 is dominant to cS1U1P1hS1S1P0 and c, cS1U1P1hS1S1P0 is dominant to c, and c is recessive to all the other alleles. This dominance hierarchy can be summarized as C > cS1U1P1ch S1S1P0> cS1U1P1h S1S1P0> c. 
-Indicate the phenotypic ratios expected of rabbits with the cross Cc × chc.

Accepted Answer

A)  1 full color : 1 chinchilla 
B)  1 full color : 1 Himalayan 
C)  1 chinchilla : 1 Himalayan 
D)  3 full color : 1 chinchilla 
E)  2 full color : 1 Himalayan : 1 albino

Question 10

The bicoid mutation (bcd-) in fruit flies is inherited as a maternal effect recessive allele. What is the expected ratio of phenotypes in the offspring of a cross between a bcd+/bcd- female and a bcd+/bcd- male?

Accepted Answer

A)  1 normal : 1 mutant 
B)  3 normal : 1 mutant 
C)  3 mutant : 1 normal 
D)  all normal 
E)  all mutant

Question 11

Assume that a human gene is imprinted. Normal individuals have one active copy of the gene, the copy inherited from their fathers. The copy inherited from their mothers is normally inactive.
In one large family a mutation in this gene occurs and this mutation results in part of the gene being deleted. The defective gene is never active regardless of the parent from which it is inherited. Individuals who carry the mutation are heterozygous and also have a normal copy of the gene whose activity depends upon which parent it was inherited from. Individuals who have no active copy of the gene have several medical problems but live long enough to have children of their own. This family includes two phenotypically normal parents who have two affected children, a son and a daughter. Which parent, father or mother, did the affected children inherit this mutation from? Why?

Accepted Answer

The answer of Assume that a human gene is imprinted....

Question 12

In domestic chickens, some males display a plumage pattern called cock feathering. Other males and all females display a pattern called hen feathering. Cock feathering is an autosomal recessive trait that is exhibited in males only.
- Two heterozygous birds are mated. What fraction of the female offspring is expected to exhibit cock feathering?

Accepted Answer

A)  0 
B)  1/8 
C)  1/4 
D)  1/2 
E)  3/4

Question 13

In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced.
- Give genotypes for comb shape of the parents in the following cross: Rose crossed with single produces 10 rose and 11 single offspring.

Accepted Answer

A)  RR PP × rr pp 
B)  RR Pp × rr pp 
C)  Rr PP × rr pp 
D)  Rr Pp × rr pp 
E)  Rr pp × rr pp

Question 14

In the endangered African watchamakallit, the offspring of a true-breeding black parent and a true-breeding white parent are all gray. When the gray offspring are crossed among themselves, their offspring occur in a ratio of 1 black : 2 gray : 1 white. Upon close examination of the coats, each hair of a gray animal is gray. What is the mode of inheritance?

Accepted Answer

A)  one gene pair with black dominant to white 
B)  one gene pair with codominance 
C)  one gene pair with incomplete dominance 
D)  two gene pairs with recessive epistasis 
E)  two gene pairs with duplicate genes

Question 15

Polydactyly is the condition of having extra fingers or toes. Some polydactylous persons possess extra fingers or toes that are fully functional, whereas others possess only a small tag of extra skin. This is an example of:

Accepted Answer

A)  variable expressivity. 
B)  complete dominance. 
C)  independent assortment. 
D)  complementation. 
E)  cytoplasmic inheritance.

Question 16

You are studying a gene that controls ossicone (horn) length in giraffes. The wild-type long-ossicone allele (L) is dominant to the mutant short-ossicone (l) allele. However, the L allele is only 60% penetrant. You cross two heterozygous giraffes. What proportion of offspring would you expect to exhibit the short-ossicone phenotype? Assume the penetrance of L applies equally to both homozygotes and heterozygotes.

Accepted Answer

A)  0.25 
B)  0.40 
C)  0.45 
D)  0.55 
E)  0.60

Question 17

Explain the differences between incomplete dominance and continuous variation.

Accepted Answer

The answer of Explain the differences between incomplete dominance and...

Question 18

In humans, blood types A and B are codominant to each other and each is dominant to O. What blood types are possible among the offspring of a couple of blood types AB and A?

Accepted Answer

A)  A, B, AB, and O 
B)  A, B, and AB only 
C)  A and B only 
D)  A, B, and O only 
E)  A and AB only

Question 19

In chickens, comb shape is determined by genes at two loci (R, r and P, p). A walnut comb is produced when at least one dominant gene R is present at one locus and at least one dominant gene P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant gene is present at the first locus and two recessive genes are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive genes are present at the first locus and at least one dominant gene is present at the second (genotype rr P_). If two recessive genes are present at the first and the second locus (rr pp), a single comb is produced. 
-Give genotypes for comb shape of the parents in the following cross: Rose crossed with walnut produces 6 walnut, 6 rose, 2 single, and 2 pea offspring.

Accepted Answer

A)  RR pp × rr PP 
B)  Rr pp × rr Pp 
C)  Rr pp × rr PP 
D)  RR pp × rr Pp 
E)  Rr pp × Rr Pp

Question 20

Two mice of the same species have different ear shapes. You find that one mouse, having ears of normal shape, was caught in a field in Kenya. The other mouse, with curled ears, was caught in the frozen tundra of Greenland. You have determined that both mice have identical genotypes at the gene loci controlling ear shape. How would you explain the differences in ear shape?

Accepted Answer

The answer of Two mice of the same species have...

Exam 5: Extensions and Modifications of Basic Principles