Autosomal Linkage Flashcards
What is meant by autosomal linkage?
Where two or more genes are located on the same non-sex chromosome. In this case, only one homologous pair is needed for all four alleles to be present. For genes that aren’t linked, two homologous pairs are needed.
What is an autosome.
Any chromosome that isn’t a sex chromosome.
Why are the genes on an autosome said to be linked?
Because they’ll stay together during the independent segregation of chromosomes in meiosis I.
Their alleles will be passed on to the offspring together.
The closer together two genes are on an autosome, the more closely they are said to be linked.
How can autosomal genes be separated during meiosis?
If crossing over occurs before independent segregation in meiosis, the genes, (and hence the alleles) of a homologous pair of autosomes will not be passed on to the offspring together.
What do you need to remember about two closely linked genes on an autosome?
Crossing over is less likely to split them up.
Why are phenotypic ratios useful?
You can use them to identify different types of linkage within inheritance.
How can you use the predicted phenotypic ratio of a dihybrid crosses between two heterozygous parents to identify autosomal linkage?
E.g. in a dihybrid cross between two heterozygous parents, you’d expect a 9:3:3:1 ratio in the offspring.
(D both: 1stD, 2ndR : 1stR, R both)
Instead, the phenotypic ratio is more likely to be that expected for a monohybrid cross between two heterozygous parents, 3:1 (D:R) because two autosomally linked alleles are inherited together.
This means a higher proportion of the offspring will have their parents’ (heterozygous) genotype and phenotype.
What is the expected phenotypic ratio of a dihybrid cross between a heterozygous parent and a homozygous recessive parent.
