Chapter 23

Question 1

When multiple phenotypes or genotypes exist in the population that can be considered “wild type,” what are they called?

Answer 1

Genetic polymorphisms

Question 2

Are blue eyes and brown eyes considered genetic polymorphisms?

Answer 2

Yes

Question 3

Are most loss-of-function alleles recessive or dominant?

Answer 3

Recessive

Question 4

Are most gain-of-function alleles recessive or dominant?

Answer 4

Dominant

Question 5

What term describes a gene where having less than two wild-type alleles results in a phenotype?

Answer 5

Haploinsufficient

Question 5

What is an example of a dominant gain-of-function allele that can lead to cancer?

Answer 5

Oncogene

Question 6

What is a dominant lethal allele?

Answer 6

An allele that allows a heterozygote to survive but prevents offspring from developing if they inherit two copies.

Question 7

What phenotype ratio is associated with dominant lethal alleles in heterozygous crosses?

Answer 7

2:1

Question 8

Name a disorder caused by a dominant lethal allele.

Answer 8

Huntington’s disease

Question 9

If a green snake becomes more yellow in a cooler environment, what might explain this?

Answer 9

A temperature-sensitive mutation

Question 9

What term describes a gene that is not always expressed due to environmental factors?

Answer 9

Incomplete penetrance

Question 10

What type of dominance occurs when a heterozygote shows a blend of two phenotypes?

Answer 10

Incomplete dominance

Question 10

In human blood type, which alleles are dominant to O?

Answer 10

A and B

Question 10

What is the term for variation in the degree to which a phenotype is expressed?

Answer 10

Expressivity

Question 11

What mechanisms allow identical DNA sequences to be expressed differently?

Answer 11

Epigenetic mechanisms (e.g., chromatin modifications or DNA methylation)

Question 12

What are temperature-sensitive alleles?

Answer 12

Alleles that produce proteins prone to denaturing at certain temperatures.

Question 13

What animals are good examples of temperature-sensitive mutations affecting pigmentation?

Answer 13

Siamese cats and Himalayan rabbits

Question 14

What is the phenotype ratio in the offspring of two pink heterozygous snakes?

Answer 14

1 red: 2 pink: 1 white

Question 15

What is the default color when a pigment gene is knocked out?

Answer 15

White

Question 15

What type of dominance occurs when both phenotypes appear distinctly in a heterozygote?

Answer 15

Codominance

Question 16

In human blood type, which alleles are codominant to each other?

Answer 16

A and B

Question 17

If a blood cell expresses the B allele, can it also receive the A sugar?

Answer 17

No

Question 18

What genotypes result in an “A” blood type?

Answer 18

AA or AO

Question 18

Does the O allele add any sugars to red blood cell proteins?

Answer 18

No

Question 19

Will the immune system of someone with A blood type attack O blood cells?

Answer 19

No

Question 20

Will the immune system of someone with A blood type attack AB blood cells? Why?

Answer 20

Yes, because AB blood contains B antigens, which are foreign to them.

Question 21

In a pedigree showing a dominant trait, what must be true of affected individuals?

Answer 21

One parent and one child must have the phenotype.

Question 22

What blood type must a person with "AB" blood be?

Answer 22

Heterozygous for the blood type gene.

Question 23

In a colony of tailless mice, why is the allele for wild-type tails not a dominant lethal?

Answer 23

A dominant lethal would result in no surviving offspring with the wild-type phenotype.

Question 24

What is a genetic polymorphism?

Answer 24

It refers to the existence of multiple phenotypes or genotypes in a population that can be considered "wild type."

Question 25

What does incomplete penetrance mean in genetics?

Answer 25

It means that a genetic disorder may not always be expressed, even if the genotype for it is present, due to environmental factors or other influences.

Question 26

What is expressivity in terms of genetics?

Answer 26

It refers to the degree to which a genotype is expressed in an organism, with some individuals showing more pronounced phenotypic traits than others, even with the same genotype.

Question 27

How can epigenetic mechanisms affect gene expression?

Answer 27

Epigenetic mechanisms, like chromatin modifications or DNA methylation, can lead to different levels of gene expression despite identical DNA sequences.

Question 28

What is a temperature-sensitive allele, and give an example.

Answer 28

A temperature-sensitive allele is one that produces a protein that can denature at certain temperatures, such as the pigmentation gene mutations in Siamese cats or Himalayan rabbits.

Question 29

If a snake changes color from green to yellow due to environmental temperature, what might this indicate?

Answer 29

This could indicate a temperature-sensitive mutation affecting the snake's pigmentation.

Question 30

What type of genetic inheritance is demonstrated when a heterozygote expresses a phenotype that is a blend of both parental phenotypes?

Answer 30

Incomplete dominance