Epistasis Flashcards
What is epistasis?
Where two non-linked genes interact, with one gene either masking or suppressing the other gene.
Describe the two types of epistasis.
Recessive epistasis - where two homozygous recessive alleles of one gene mask the expression of another allele on a another gene.
Dominant epistasis - where one dominant allele (of one gene) masks the expression of multiple other alleles (on another gene).
Explain how the with expression of the widows peak gene is masked by the baldness genes.
Explain how the with expression of the how one gene can mask the expression of another gene in flowers.
How do multiple alleles of a gene arise? (2)
mutations
which are at different positions in the gene.
The production of pigment in rabbit fur is controlled by two genes.
One gene controls whether any pigment is made.
This gene has three alleles.
Allele A codes for the production of one form of the enzyme tyrosinase, which converts tyrosine into a black pigment.
Allele A codes for the production of a second form of the enzyme, which becomes inactive at temperatures close to a rabbit’s core body temperature, so only the face, ears, legs and tail are pigmented.
A third allele, a, fails to code for a functional tyrosinase.
The other gene controls the density of pigment in the fur. This gene has two alleles. Allele B is dominant and results in the production of large amounts of pigment, making the fur black.
Allele b results in less pigment, so the fur appears brown.
The table shows some genotypes and phenotypes.
a) what do the dashes represent in the genotype of the black rabbit ?
b) Give all the possible genotypes for a Himalayan rabbit with black face, legs, ears and tail.
a) either a dominant or recessive allele
b)
The production of pigment in rabbit fur is controlled by two genes.
One gene controls whether any pigment is made.
This gene has three alleles.
Allele A codes for the production of one form of the enzyme tyrosinase, which converts tyrosine into a black pigment.
Allele A codes for the production of a second form of the enzyme, which becomes inactive at temperatures close to a rabbit’s core body temperature, so only the face, ears, legs and tail are pigmented.
A third allele, a, fails to code for a functional tyrosinase.
The other gene controls the density of pigment in the fur. This gene has two alleles. Allele B is dominant and results in the production of large amounts of pigment, making the fur black.
Allele b results in less pigment, so the fur appears brown.
c) Suggest an explanation for the pigment being present only in the tail, ears, face and legs of a Himalayan rabbit.
d) Using the information given, explain why the phenotypes of rabbits with AABB and Aa^BB genotypes are the same.
c) temperature lower at extremities; enzyme active/not denatured.
d) if allele A is present (normal) tyrosinase / enzyme is produced, so it does not matter what other allele is present.
Heterozygote is same phenotype as double dominant in terms of enzyme produced
phenotype: rabbit is black as both have alleles A and B
