Epistasis and gene interaction notes

Epistasis

The interaction between genes where the effects of one gene mask or modify the effects of another gene.

True or False: Epistasis can only occur between two genes.

False. Epistasis can occur between multiple genes, influencing phenotypic expressions.

Example of epistasis in plants

In sweet corn, the A and B genes determine color; A can mask B's effect.

What is a double recessive epistasis?

A case where two recessive alleles at different loci completely mask the phenotype of other alleles.

Fill in the blank: In epistasis, the gene that masks is called the ______.

epistatic gene.

Comparison: Epistasis vs. Dominance

Epistasis involves interactions between different genes; dominance occurs within a single gene's alleles.

Cause → Effect: Gene A is epistatic to Gene B.

If Gene A is present, the phenotype associated with Gene B does not manifest.

What are modifier genes?

Genes that alter the expression of another gene without completely masking it.

Example of dominant epistasis

In squash, a dominant allele at one locus can mask the expression of alleles at another locus.

True or False: All gene interactions are epistatic.

False. Not all gene interactions lead to epistasis; some may result in additive effects.

What is a hypostatic gene?

The gene whose effects are masked by an epistatic gene in a genetic interaction.

Fill in the blank: The phenotypic ratio for recessive epistasis is often ______.

9:3:4 (in a typical dihybrid cross).

Additive Gene Interaction

The combined effects of multiple alleles where each allele contributes equally to the phenotype.

True or False: Epistasis is always additive.

False. Epistasis can be non-additive, where one gene masks the expression of another.

Fill in the blank: Complementary gene interaction typically requires ______ genes to express a phenotype.

two

Question: How does recessive epistasis work?

When a recessive allele masks the expression of another gene, regardless of its allele.

Dominant vs Recessive Epistasis

Dominant epistasis: one dominant allele masks another. Recessive epistasis: a recessive allele masks another.

Example: Dominant epistasis in squash.

In summer squash, the presence of one dominant allele (W) can mask the expression of color alleles (Y/y).

Question: What is duplicate gene interaction?

When two different genes can produce the same phenotype, requiring only one dominant allele from either gene.

Cause → Effect: Duplicate recessive epistasis

Cause: Two recessive alleles Effect: Phenotype only shows if both alleles are present.

What is gene interaction?

The phenomenon where the effect of one gene is modified by one or several other genes.

Example of additive gene effects.

Height in plants often shows additive effects, where each contributing allele increases height.

Question: What role do modifier genes play?

Modifier genes can influence the expression of another gene, enhancing or suppressing its effects.

True or False: All gene interactions are predictable.

False. Many gene interactions can lead to unexpected phenotypic ratios due to complex pathways.

Epistasis in Labrador Retrievers?

The interaction between two genes determines coat color; a gene for pigment (B) and one for color expression (E). If 'ee', no pigment is produced, resulting in a yellow coat regardless of the B genotype.

True or False: Epistasis affects only dominant genes.

False. Epistasis can involve both dominant and recessive alleles, influencing trait expression in various combinations.

Fill in the blank: In corn, the _____ gene can mask the expression of purple kernel color.

The 'W' gene (for waxy) interacts with the color gene, leading to a different phenotype.

Comparing sweet and bitter almonds?

Bitter almonds contain a gene that, when expressed, produces cyanogenic compounds. Sweet almonds are epistatic to this gene, masking its expression.

Cause → Effect: Coat color in mice?

Cause: Agouti gene (A) interacts with extension gene (E). Effect: Determines whether a mouse appears brown or black.

Example of epistasis in agriculture?

In crop breeding, certain traits like drought resistance can be controlled by multiple interacting genes, affecting yield. Selecting for one trait can inadvertently change others.

What is complementary gene interaction?

It occurs when two genes work together to produce a specific phenotype, such as flower color where both genes need to be dominant for color to be expressed.

True or False: Epistasis can complicate traits in breeding programs.

True. It makes predicting phenotypes based on genotypes more difficult due to interactions among multiple genes.

Question: How does epistasis influence human traits?

Epistasis can affect traits such as skin color, where multiple genes interact to determine the final phenotype.

What happens in sweet pea flowers?

The combination of two genes determines flower color; dominant alleles may interact to produce a range of colors, exemplifying epistatic interaction.

Fill in the blank: The _____ gene in potatoes can mask the effects of the color gene.

The 'R' gene controls resistance to late blight, which may mask other traits related to color.

Example of epistasis in fitness?

In some populations, genes that influence metabolic pathways can interact, affecting overall fitness and survival under environmental stressors.