Module 2

Question 1

Simple Mendelian

Answer 1

Inheritance pattern: Inheritance of alleles follows strict dominant/recessive relationship

Molecular explanation: 50% of protein produced by one copy of the dominant allele is sufficient to produce dominant trait

Question 2

Incomplete penetrance

Answer 2

Inheritance pattern: Dominant phenotype is not expressed even with dominant allele present

Molecular explanation: Environmental influences or other interfering genes

Question 3

Incomplete dominance

Answer 3

Inheritance pattern: Heterozygote has a phenotype that mixes each homozygote (ex. Red X White = Pink)

Molecular explanation: 50% of protein produced by a single copy of the functional allele in the heterozygote is insufficient to express trait

Question 4

Overdominance

Answer 4

Inheritance pattern: Heterozygote has a trait conferring greater level of reproductive success than either homozygote

Molecular explanation: (1) Cells have increased resistance to infection (e.g., sickle cell disease and malaria), (2) produce more protein dimers with enhanced function, or (3) produce proteins that function under wider range of conditions

Question 5

Codominance

Answer 5

Inheritance pattern: Heterozygote expresses both alleles simulatenously (e.g., AB blood type)

Molecular explanation: Codominant alleles function slightly differently with unique protein functions

Question 6

X-linked

Answer 6

Inheritance pattern: Genes located on X chromosome

Molecular explanation: Males express the only copy of an X-linked allele they carry

Question 7

Sex-influenced

Answer 7

Inheritance pattern: The effect of sex on phenotype (ex. scurs in cattle, dominant in males only)

Molecular explanation: Sex hormones regulate molecular expression of genes, influencing phenotypic effects

Question 8

Sex-limited

Answer 8

Inheritance pattern: Trait occurs in only one of two sexes (ex. breast development)

Molecular explanation: Sex hormones primarily produced in one sex are essential for an individual to display a particular phenotype

Question 9

Lethal alleles

Answer 9

Inheritance pattern: Has potential of causing death of organism

Molecular explanation: Commonly loss-of-function alleles encoding proteins vital to survival, often arise from mutations

Question 10

Molecular explanations for recessive traits being based on loss of function mutations

Answer 10

1. Homozygous for recessive allele
2. Only have one copy of allele and it is recessive (X-linked)

Question 11

3 Common explanations for dominant mutant alleles

Answer 11

1. Gain of function mutations - change in gene or function of protein giving it abnormal function
2. Dominant-negative mutations - mutant protein acts antagonistically and counteracts normal protein function
3. Haploinsufficiency - dominant allele is a loss-of-function allele, heterozygotes exhibit abnormal phenotype

Question 12

Example of environment impacting outcome of traits

Answer 12

Temperature-sensitive alleles (arctic fox coats that are white in winter, brown in summer)

Question 13

Gene interaction

Answer 13

How allelic variations in two different genes affect a single trait

Question 14

Expressivity

Answer 14

The degree to which a trait is expressed (variation)

Question 15

Epistasis

Answer 15

Alleles from one gene mask the phenotypic effects of another

Question 16

Complementation

Answer 16

Two parents with recessive phenotype produce offspring with a wild phenotype

Question 17

Gene redundancy

Answer 17

One gene compensates for the loss of function of another gene (paralog)

Question 18

Pseudoautosomal inheritance

Answer 18

Refers to the few genes found on both the X and Y chromosome

Question 19

Pleiotropy

Answer 19

Multiple effects of a single gene on the phenotype of an organism, due to product affecting cell function in multiple ways or expression of gene in different cell types

(ex. cystic fibrosis, melanoblast migration)