Gene Interactions & Epigenetics Flashcards
What is epistasis?
The interaction between two (or more) genes that control a single phenotype
Main types include one mutation affecting the phenotype of another mutation, both mutations having no phenotype but the double mutant exhibiting a phenotype, and both mutations having the same phenotype but the double mutant showing a different phenotype.
What is the phenotypic ratio observed in a monohybrid cross with complete dominance?
3:1
This ratio indicates that one phenotype is dominant over the other.
What is incomplete dominance?
A genetic situation where one allele does not completely dominate another, resulting in a phenotype that is a blend of both alleles.
Example: In a cross between red and white flowers, the offspring may be pink.
What are the genotypes and phenotypes resulting from a Bb x Bb cross?
- 1 BB (black)
- 2 Bb (black)
- 1 bb (white)
This results in a 3:1 ratio of black to white phenotypes.
What is the definition of genomic imprinting?
Heritable changes in gene expression that do not involve alterations of the DNA sequence of the genome.
This can lead to one allele being expressed while the other is silenced depending on its parent of origin.
What is the significance of the W gene in mouse coat color?
The W gene encodes the Kit protein, essential for the survival and migration of melanoblasts, the precursors of melanocytes.
The W allele is associated with dominant white/white spotting.
How does the albino (c) allele affect coat color in mice?
The albino allele is a recessive loss of function mutation in the enzyme tyrosinase required for melanin synthesis.
This results in no melanin production, leading to white fur and red eyes.
What is the expected ratio of phenotypes when crossing brown and albino mice?
9:4:3
This ratio results from recessive epistasis, where the albino phenotype prevails over the brown phenotype.
What is meant by ‘dominant epistasis’?
A situation where a dominant allele masks the effects of other alleles at different loci.
For example, the W allele being dominant white can mask the presence of other coat color genes.
Fill in the blank: The gene that encodes for the Agouti signalling protein (ASP) is the _______ gene.
A gene
What is the parent-of-origin effect in genomic imprinting?
The phenomenon where the expression of a gene depends on whether it is inherited from the mother or the father.
Example: In the Igf2 gene, only the paternal copy is expressed while the maternal copy is silenced.
True or False: Epigenetics involves changes to the DNA sequence.
False
Epigenetics refers to heritable changes in gene expression without changes in the DNA sequence.
What is the phenotypic ratio observed in a monohybrid cross with incomplete dominance?
1:2:1
This ratio shows one homozygous dominant, two heterozygous, and one homozygous recessive phenotype.
What are the main types of epistasis?
- Recessive epistasis
- Dominant epistasis
Each type describes how one gene can mask or modify the expression of another gene.
What are the implications of maternal imprinting in genomic imprinting?
The maternal allele is imprinted and silenced while the paternal allele is preferentially expressed.
This can lead to specific phenotypic outcomes based on which parent’s allele is active.
