Lecture 12 - Genetic Interactions Flashcards
What are the two main types of genetic interactions?
Allelic interactions: Between alleles of the same gene.
Non-allelic interactions: Between different genes.
What is dominance in allelic interactions?
Dominance reflects how alleles of a single gene interact in heterozygotes, determining phenotype.
What is complete dominance?
The heterozygote is phenotypically identical to the homozygote for the dominant allele due to sufficient protein production.
What is haplosufficiency vs. haploinsufficiency?
Haplosufficiency: One functional allele produces enough protein (mutation is recessive).
Haploinsufficiency: One functional allele is insufficient (mutation is dominant).
What is a dominant negative mutation?
A mutant allele interferes with wild-type protein, often in multimeric proteins, disrupting function.
What are lethal alleles?
Mutations that compromise essential genes, often fatal in homozygous form, altering phenotypic ratios (e.g., 2:1).
What is an allelic series?
A group of alleles for one gene showing different dominance relationships (e.g., black > brown > light brown in coat colour).
What are non-allelic interactions?
Interactions between different genes that affect the same phenotype, often within a shared pathway.
What is epistasis?
When one gene masks the effect of another at the phenotypic level.
What is recessive epistasis?
A recessive allele at one gene overrides another gene’s phenotype (e.g., flower colour pathway).
What is dominant epistasis?
A dominant allele inhibits a pathway, masking other phenotypes (e.g., white phenotype from W allele).
What is duplicate gene action?
Two genes with the same function provide redundancy; one functional allele from either gene suffices for the phenotype.
What is complementary gene action?
Both genes are required for the phenotype; mutations in either gene produce the same mutant phenotype.
What is a complementation test?
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.
What are modifiers?
Mutations that alter the expression of another gene (e.g., dilute coat colour in cats).
What are suppressors?
Mutations that reverse the effect of another mutation, restoring the wild-type phenotype.
What are non-allelic interactions in haploid organisms?
Interactions like epistasis and suppression, observed in simpler organisms (e.g., yeast or bacteria).
What is a phenotypic ratio alteration caused by lethal alleles?
Typical Mendelian ratio of 1:2:1 becomes 2:1 due to homozygous lethality.
What is genetic redundancy?
Two or more genes perform the same function.
Loss of one gene is compensated by the other.
Example: Duplicate gene action.
How does complementary gene action affect biochemical pathways?
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.
What is the role of suppressor mutations in genetic studies?
Suppressors help identify pathways and interactions by restoring wild-type phenotypes.
They can act dominantly or recessively.
What is a modifier mutation?
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.
What are additive interactions in haploid organisms?
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.
What is the 9:3:3:1 phenotypic ratio?
A classic Mendelian dihybrid ratio seen in independent assortment of two genes.
Epistatic interactions modify this ratio in specific ways.
How does recessive suppression differ from epistasis?
Recessive suppression restores the wild-type phenotype.
Epistasis masks the effect of another gene without restoring the wild type.
