17.7 Autosomal linkage Flashcards
What is autosomal linkage
Where two or more genes are carried on the same autosome
What is an autosome
One of the 23 chromosomes in our body, but not the 23rd one which is a sex chromosome
What would the gametes be if genes A and B occurred on the same chromosome
Only one homologous pair would be needed if all four alleles are to be present
So eg in AaBb
So on one chromosome it would be AB (with A at the top of the chromos and B at the bottom of them)
on the other chromosome in the pair, it would be aa at the top of them and bb at the bottom
So the gametes are either AB or ab
In autosomal linkage, do the genes segregate in accordance to Mendels law of independent assortment
No, as long as there is no crossing over, and all the linked genes remain together during meiosis so pass into gametes and the offspring, together
How would independent assortment work if the genes A and B were on different chromosomes
If the genes A and B with heterozygous alleles were on different chromosomes, there are 4 combinations of the alleles in the gametes:
AB, Ab, aB, ab
However if the two genes are linked and if there is no crossing over, there are only two possible combinations of the alleles in the gametes: AB and ab
They are always written with A and B (the dominant ones) on one chromatid, and the recessive a,b on the other
So the gametes will be AB and ab
How does crossing over during Meiosis affect autosomal linkage
Because when the chromatids cross over in meiosis, the alleles may swap
So a chromatid that used to have AB may now have Ab
