Chapter 5

Question 1

what does the phrase “gene interactions” refer to?

Answer 1

the ways genes collaborate or interact to influence a phenotype

Question 2

what are 4 important types of gene interactions?

Answer 2

1. There may be more than two alleles for a given locus within a population
2. Dominance of one allele over another may not be complete
3. Two or more genes may affect a single trait
4. The expression of a trait may depend on the interaction of more than one gene and/or the interaction of genes with nongenic factors

Question 3

what does the phenotype depend on?

Answer 3

the action of proteins that are encoded by a specific protein

Question 4

what does haplosufficient mean?

Answer 4

one copy of an allele is enough for wild-type phenotype
-the dominant allele is this

Question 5

what does haploinsufficient mean?

Answer 5

one copy of an allele is not enough for wild-type phenotype
-the recessive allele is this

Question 6

what is a dominant negative mutation?

Answer 6

these mutations are dominant due to loss of
function of the multimeric protein due to an amino acid change in one subunit
-These are negative mutations due to their “spoiler” effect on the protein as a whole

Question 7

what is particularly subject to dominant negative mutations?

Answer 7

Multimeric proteins, composed of two or more polypeptides that join together to form a functional protein

Question 8

what is incomplete dominance?

Answer 8

also called partial dominance and is when
heterozygous individuals display intermediate
phenotypes between either homozygous type

Question 9

what is codominance?

Answer 9

leads to heterozygotes with a different phenotype than that of either homozygote

Question 10

Antigens relative to blood type?

Answer 10

-The A blood type involves the presence of one antigen on the blood cell surfaces
-type B the presence of a different antigen
-Type AB people have both antigens
-type O people have neither

Question 11

what is a characteristic of lethal alleles?

Answer 11

Because they are recessive, lethal
alleles can “hide” in heterozygotes
and persist in a population

Question 12

when is a trait penetrant?

Answer 12

when the phenotype is consistent with the genotype

Question 13

when is a trait nonpenetrant?

Answer 13

when the genotype fails to consistently produce the expected phenotype

Question 14

what is incomplete penetrance?

Answer 14

when traits are occasionally nonpenetrent

Question 15

what is variable expressivity?

Answer 15

the same genotype produces a range of phenotypes that vary in degree

Question 16

what are gene-environment interactions?

Answer 16

when the environment influences the phenotype that perhaps explains incomplete penetrance and variable expressivity in some
instances.

Question 17

what is the “one gene-one enzyme” hypothesis?

Answer 17

where a single gene encodes a single enzyme

Question 18

what is a prototroph?

Answer 18

strain that can synthesize all compounds required for growth

Question 19

what is an auxotroph?

Answer 19

strain that is unable to synthesize all compounds required for growth

Question 20

what is genetic dissection?

Answer 20

Determining the order of biochemical pathways using single-gene mutants and identifying the point at which the pathways is blocked

Question 21

all mutants can grow on what part of the pathway?

Answer 21

the end-product

Question 22

what is epistasis?

Answer 22

Gene interaction where alleles at one gene influence the function of alleles at another gene.

Question 23

what is complementation?

Answer 23

complementary gene interaction occurs when genes must act in tandem to produce a phenotype
-wild-type action from both genes is required to produce the wild-type phenotype
-mutation of one or both genes produce a mutant phenotype

Question 24

how do you determine what mutants are part of the same complementation group?

Answer 24

mutants that do not complement each other are part of the same complementation group, and mutations are on the same gene

Question 25

What does the number of complementation groups tell you?

Answer 25

the number of genes involved in a trait