Lecture 12 - Genetic Interactions

Question 1

What are the two main types of genetic interactions?

Answer 1

Allelic interactions: Between alleles of the same gene.

Non-allelic interactions: Between different genes.

Question 2

What is dominance in allelic interactions?

Answer 2

Dominance reflects how alleles of a single gene interact in heterozygotes, determining phenotype.

Question 3

What is complete dominance?

Answer 3

The heterozygote is phenotypically identical to the homozygote for the dominant allele due to sufficient protein production.

Question 4

What is haplosufficiency vs. haploinsufficiency?

Answer 4

Haplosufficiency: One functional allele produces enough protein (mutation is recessive).

Haploinsufficiency: One functional allele is insufficient (mutation is dominant).

Question 5

What is a dominant negative mutation?

Answer 5

A mutant allele interferes with wild-type protein, often in multimeric proteins, disrupting function.

Question 6

What are lethal alleles?

Answer 6

Mutations that compromise essential genes, often fatal in homozygous form, altering phenotypic ratios (e.g., 2:1).

Question 7

What is an allelic series?

Answer 7

A group of alleles for one gene showing different dominance relationships (e.g., black > brown > light brown in coat colour).

Question 8

What are non-allelic interactions?

Answer 8

Interactions between different genes that affect the same phenotype, often within a shared pathway.

Question 9

What is epistasis?

Answer 9

When one gene masks the effect of another at the phenotypic level.

Question 10

What is recessive epistasis?

Answer 10

A recessive allele at one gene overrides another gene’s phenotype (e.g., flower colour pathway).

Question 11

What is dominant epistasis?

Answer 11

A dominant allele inhibits a pathway, masking other phenotypes (e.g., white phenotype from W allele).

Question 12

What is duplicate gene action?

Answer 12

Two genes with the same function provide redundancy; one functional allele from either gene suffices for the phenotype.

Question 13

What is complementary gene action?

Answer 13

Both genes are required for the phenotype; mutations in either gene produce the same mutant phenotype.

Question 14

What is a complementation test?

Answer 14

A test to determine if mutations are in the same or different genes:

Complementation (WT): Mutations are in different genes.
No complementation (mutant): Mutations are in the same gene.

Question 15

What are modifiers?

Answer 15

Mutations that alter the expression of another gene (e.g., dilute coat colour in cats).

Question 16

What are suppressors?

Answer 16

Mutations that reverse the effect of another mutation, restoring the wild-type phenotype.

Question 17

What are non-allelic interactions in haploid organisms?

Answer 17

Interactions like epistasis and suppression, observed in simpler organisms (e.g., yeast or bacteria).

Question 18

What is a phenotypic ratio alteration caused by lethal alleles?

Answer 18

Typical Mendelian ratio of 1:2:1 becomes 2:1 due to homozygous lethality.

Question 19

What is genetic redundancy?

Answer 19

Two or more genes perform the same function.

Loss of one gene is compensated by the other.

Example: Duplicate gene action.

Question 20

How does complementary gene action affect biochemical pathways?

Answer 20

Loss of function in either gene prevents the completion of the pathway.
Example: Both genes A and B are required to produce purple pigment; mutations in either result in white flowers.

Question 21

What is the role of suppressor mutations in genetic studies?

Answer 21

Suppressors help identify pathways and interactions by restoring wild-type phenotypes.
They can act dominantly or recessively.

Question 22

What is a modifier mutation?

Answer 22

A mutation that changes the effect of another gene, often altering the phenotype subtly.
Example: Dilution locus in cats modifies coat colour without masking it.

Question 23

What are additive interactions in haploid organisms?

Answer 23

Additive effects occur when two mutations combine to produce a summed phenotype.
Example: Loss of function in gene A (-2) and gene B (-3) results in phenotype -5.

Question 24

What is the 9:3:3:1 phenotypic ratio?

Answer 24

A classic Mendelian dihybrid ratio seen in independent assortment of two genes.
Epistatic interactions modify this ratio in specific ways.

Question 25

How does recessive suppression differ from epistasis?

Answer 25

Recessive suppression restores the wild-type phenotype.

Epistasis masks the effect of another gene without restoring the wild type.