Linked Genes

My AP Biology Thoughts Unit 5 Heredity

Welcome to My AP Biology Thoughts podcast, my name is Victoria Villagran and I am your host for episode #101 called Unit 5 Heredity: Linked Genes. Today we will be discussing linked genes and their characteristics!

Segment 1: Introduction to Linked Genes

• Linked Genes
• A form of non-mendelian inheritance
• Discovered by Thomas Hunt Morgan, using the fruit fly Drosophila melanogaster
• Genes on the same chromosome, making them more likely to be inherited together
• If crossing over occurs, then they are no longer linked it will look like independent assortment
• If they are linked, they will not assort independently and the ratios of the offspring will different
• If there are more parental phenotypes, then it is linked
• If there are more recombinant then is it non-linked
• The recombination frequency is very small. If the genes are far apart on a chromosome, or on different chromosomes, the recombination frequency is 50%. ... If the recombination frequency is less than 50% we say the two loci are linked
• Recombinant and Map Units:
• The farther apart the genes are on the chromosome, the more likely they are to separate because of crossing over resulting in recombinant offspring
• Recombinant offspring generally appear in proportions related to the recombination frequency between the two genes:
• Calculated by dividing the number of recombinant progeny by the total number of progeny
• This can be used to calculate map units or how far away the genes are from each other

Segment 2: More About Linked Genes

• Let’s look at fruit flies
• If linkage held true, then F1 would only have the two parental phenotypes in a 1:1 ratio
• The genes for eye color and the genes for wing length are on the same chromosome, thus are inherited together.
• A cross between gray and normal with black vestigial
• There are more parental phenotypes with 965 and 944 than recombinant with 206 for gray and vestigial, and 185 with black normal. There is an expected 575 frequency for each...