Linkage and Epistasis Flashcards
What is epistasis?
When one gene influences the expression of the other
What is the genotype of the offspring when a dihybrid homozygous dominant and dihybrid homozygous recessive reproduce?
100% heterozygous, so will show dominant traits
What may change the ratio when dihybrid heterozygous reproduce?
- autosomal linkage
- crossing over
What is autosomal linkage?
when the 2 genes are located on the same chromosome (not the sex chromosome)
How does linkage impact gametes?
the alleles on the same chromosome will be inherited together
Why are males more commonly affected by sex-linked disorders (in humans)?
- X chromosomes are longer than Y chromosomes
- X chromosomes carry more genes
males only have 1 X chromosome - only need 1 recessive allele is present as no other allele present
- whereas females would need 2 recessive alleles to be affected
Why might mendelian patterns of inheritance not be followed?
- linked genes
- epistasis
- random fertilisation
- small sample size
Why don’t X and Y chromosomes form a bivalent?
not homologous and are different in size, Y is shorter than X
What is dominant epistasis?
the presence of a dominant allele masks or hides the expression of another gene in the phenotype
What is recessive epistasis?
when 2 recessive alleles mask or hide the expression of another gene in the phenotype
Explain why 2 alleles might be inherited together more frequently
- autosomal linkage
- linked genes are close together and crossing over is less-likely
- if 3 marks: REFERENCE GAMETES
Why does linkage prevent predicted mendelian ratios from being followed?
- genes are likely to be inherited together
- crossing over is less likely
Why can recessive alleles reach higher frequency than dominant alleles?
- people can carry recessive alleles without being affected
- more likely to reproduce than those affected with a condition
- more likely to be passed on than dominant
