Genetics Chapter 5

Question 1

Wild-type allele

Answer 1

the most prevalent version of a gene in wild populations (i.e., the “normal” version of a gene)

Question 2

Genetic polymorphism

Answer 2

Genes can have more than 1 common allele that can be considered wild-type

Question 3

Recessive Alleles/Mutant allele

Answer 3

• A less common version of a gene
• Due to random mutations that
  occur in DNA
  Most random mutations produce alleles that are inherited in a recessive fashion
  Ex: recessive alleles in pea plants were the mutant alleles
  Recessive mutant alleles typically produce less functional protein
  Either because the protein is defective or they produce lower levels of the functional protein

Question 4

Dominant mutant alleles

Answer 4

Gain-of-function mutations - The gene gains a new or abnormal function
May be overexpressed, producing higher levels of the protein

Question 5

Dominant mutant alleles example

Answer 5

Example: p53
p53 is a tumor suppressor gene
if mutated, p53 can cause cancer
p53 upregulates genes inappropriately, changing the “identity” of the cell

Question 6

Haploinsufficiency

Answer 6

Sometimes mutant alleles are dominant
The mutant is a loss-of-function allele, and one wild-type copy is not enough to provide function
Example: Polydactyly in humans (extra fingers in babies)

The dominant mutant allele loses its function so that a heterozygous individual shows an abnormal phenotype or disease phenotype.

Question 7

Loss of function mutations

Answer 7

May have no effect on phenotype
Inactive or a less active protein
One gene can compensate for the loss of another

Question 8

Gain of function mutations

Answer 8

Gene gains a new or abnormal function
May be overexpressed, producing higher levels of proteins
Example: p53 gene

The product of the dominant mutant allele is expressed in cells where it is not normally active, leading to a change in phenotype.

Question 9

Penetrance

Answer 9

portion of individuals with a given phenotype associated with a specific allele

→a population

Example: incomplete penetrance→polydactyly

Question 10

Expressivity

Answer 10

The degree (intensity) of a certain phenotype for a given genotype

→ single individual

Question 11

Incomplete dominance

Answer 11

when one allele is not completely expressed
The heterozygous will have an intermediate state

Question 12

Overdominance

Answer 12

when a heterozygous produces a phenotype more extreme or better than that of the homozygote

Heterozygous has greater reproductive success than either homozygous

It is also called: heterozygote advantage or hybrid vigor

Question 13

Codominance

Answer 13

is when the heterozygous genotype expresses both alleles (red X white= red + white spots

Question 14

how overdominance can occur

Answer 14

• Sickle-cell anemia
  Autosomal recessive disorder
  Affected individuals produce abnormal form of hemoglobin
• Two alleles:
  HbA→normal hemoglobin, hemoglobin A
  HbS→ abnormal hemoglobin, hemoglobin S
• Malaria incidences correlates with increased HbS allele frequency
  Heterozygotes are malaria-resistant

Question 15

Sex-linked

Answer 15

associated with one sex or the other, carried by a sex chromosome

Question 16

Sex-limited

Answer 16

traits that occur only in one of the two sexes

Responsible for sexual dimorphism (differences in appearance between the sexes of an animal in addition to difference between the sexual organs themselves).

Might be autosomal or sex-linked

Question 17

Sex-influnced

Answer 17

an allele is dominant in on sex but recessive in the other
Sex influence is a phenomenon of heterozygotes
This doesn’t mean sex-linked
Most sex-influenced traits are autosomal

Question 18

Essential genes

Answer 18

are required for survival

Question 19

Lethal allele

Answer 19

Lethal allele: has the potential to cause the death of an organism (usually in essential genes)

Examples: mutations in genes that promote cell division
Hungtington’s disease

Question 20

Conditional lethal alleles

Answer 20

kill an organism only under certain environmental conditions

Temperature -sensitive (ts) lethals: proteins misfold at higher temperatures, becoming nonfunctional

Question 21

Semi Lethal alleles

Answer 21

kill some individuals in a population, but not all of them
Environmental factors and other genes may help prevent detrimental effects of semi lethal genes

Question 22

The enzyme glycosyl transferase has 3 common alleles in human

Answer 22

(i, I^A, I^B)

Codominance

ABO locus has 3 main allelic forms: A, B, O
Allele i encodes a nonfunctional enzyme
Alleles I^A & I^B are codominant

Question 23

Pleiotropy and why it occurs and example

Answer 23

multiple effects of a single gene on the phenotype of an organism

Occur:
The gene product may affect cell function in multiple ways
The gene may be expressed in different cell types
The gene may be expressed at different stages of development

Example: cystic fibrosis→ a disease with MANY SYMPTOMS caused by ONE gene

Question 24

Epistasis

Answer 24

one gene affects the expression of a different gene

Example: baldness gene covers up the genes for hair color)

Epistatic interactions often arise because two different proteins participate in a common cellular function

Question 25

Gene interactions

Answer 25

occur when two or more different genes influence the outcome of a single trait

Question 26

Gene Modification

Answer 26

allele of one gene modifies the phenotypic outcome of a different gene

Question 27

Gene Redundancy

Answer 27

loss of function alleles may have no effect on phenotype

One gene compensate for the loss another

Question 28

Dominant-negative mutation

Answer 28

The product of the dominant mutant allele interacts with the product of the normal allele causing an altered phenotype.

Question 29

Brittle bone disease is caused by a mutation in a gene that codes for collagen fibers. The product of the mutant allele binds to normal collagen and disrupts proper fiber formation. The mutation can be described as a ______ mutation.

Answer 29

dominant-negative

Question 30

If a heterozygous individual shows a disease phenotype despite having one functional allele, the inheritance pattern is called

Answer 30

haploinsufficiency

Question 31

The pattern observed when a heterozygote does not show the trait associated with the dominant allele is

Answer 31

incomplete penetrance

Question 32

A mutant allele can exert its dominance over a wild-type allele by which of the following changes?

Answer 32

dominant-negative mutations

haploinsufficiency

gain-of function mutations

Question 33

The phenotypic range for individuals with a specific genotype is called the

Answer 33

norm of reaction