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
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 genotype
they are linked, so they did not assort independently and the ratios of actual offspring were different from the expected
Segment 3: Connection to Heredity
Linked genes and heredity, specific non-mendelian inheritance are connected
Heredity or inheritance is the passing on of traits or genetic information from one generation to the the next, and linked genes are a specific way how these genes are passed on from being on the same chromosome and not independently assorted, giving more parental phenotypes. For example, the farther apart the genes are on the chromosome, the more likely they are to separate because of crossing over resulting in recombinant offspring. The location and space between genes dictate the way they will be inherited by new generations.
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"Ice Flow" Kevin MacLeod (incompetech.com)
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