Genetics Chapter 4

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1

With incomplete dominance, a likely ratio resulting from a monohybrid cross would be ________.
A) 3:3
B) 1:2:2:4
C) 1:2:1
D) 9:3:3:1
E) 3:1

C) 1:2:1

2

A situation in which there are more than two alternative forms of a given gene would be called ________.
A) multiple alleles
B) alternation of generations
C) codominance
D) incomplete dominance
E) hemizygosity

A) multiple alleles

3

A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.
A) codominance
B) epistasis
C) dominance
D) recessiveness
E) additive alleles

B) epistasis

4

Typical ratios resulting from epistatic interactions in dihybrid crosses would be ________.
A) 9:3:3:1, 1:2:1
B) 1:1:1:1, 1:4:6:4:1
C) 9:3:4, 9:7
D) 1:2:2:4:1:2:1:2:1
E) 3:1, 1:1

C) 9:3:4, 9:7

5

With which of the following would hemizygosity most likely be associated?
A) codominance
B) incomplete dominance
C) trihybrid crosses
D) X-linked inheritance
E) sex-limited inheritance

D) X-linked inheritance

6

A mutation in a gene often results in a reduction of the product of that gene. The term for this type of mutation is ________.
A) codominance
B) incomplete dominance
C) gain of function
D) multiple allelism
E) loss of function or null (in the case of complete loss)

E) loss of function or null (in the case of complete loss)

7

Because of the mechanism of sex determination, males of many species can be neither homozygous nor heterozygous. Such males are said to be ________.
A) dominant
B) hemizygous
C) recessive
D) complementary
E) None of the answers listed is correct.

B) hemizygous

8

With multiple alleles, there can be more than two genetic alternatives for a given locus.

TRUE

9

With both incomplete dominance and codominance, one expects heterozygous and homozygous classes to be phenotypically identical.

FALSE

10

The ABO blood group locus in humans provides an example of epistasis.

FALSE

11

Sex-limited inheritance is the same as sex-linked inheritance.

FALSE

12

A conditional mutant is one whose expression is influenced by some environmental condition.

TRUE

13

A typical epistatic ratio is 9:3:4.

TRUE

14

A 9:7 ratio indicates incomplete dominance

FALSE

15

Pattern baldness and hen/cock feathering in fowl are examples of X-linked inheritance.

FALSE

16

Penetrance specifically refers to the expression of lethal genes in heterozygotes.

FALSE

17

Expressivity is the term used to describe the balanced genetic output from a hemizygous condition.

FALSE

18

Hemizygosity is the term one uses to describe the state of a gene that has no allele on the opposing chromosome.

TRUE

19

Genomic imprinting occurs when one allele converts another.

FALSE

20

Genomic anticipation refers to observations that a genetic disorder occurs at an earlier age in successive generations, whereas genetic imprinting occurs when gene expression varies depending on parental origin.

TRUE

21

"Gain of function" mutations are generally dominant since one copy in a diploid organism is sufficient to alter the normal phenotype.

TRUE

22

Assume that a mutation occurs in the gene responsible for the production of hexosaminidase A, such that only about 50% of the enzyme activity is found in the heterozygote compared with a homozygous normal individual. If heterozygotes are phenotypically normal, we would say that the mutant allele is recessive to its normal allele.

TRUE

23

Alleles that are masked by an epistatic locus are said to be hypostatic to the genes at that locus.

TRUE

24

One result of X-linkage is a crisscross pattern of inheritance in which sons express recessive genes of their fathers and daughters express recessive genes of their mothers.

FALSE

25

The term expressivity defines the percentage of individuals who show at least some degree of expression of a mutant genotype.

FALSE