lecture 10.pptx - Genetics Lecture 10 Mar 30 2020 Chapter 5...

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Genetics Lecture 10 Mar. 30, 2020
Chapter 5 When two traits have the same pattern of inheritance they are said to be linked . Linkage arises from the two genes being on the same chromosome. In this situation Mendel’s Law of Independent Assortment does not apply . 2
3 Suppose gene A is linked to B, A is linked to C, and B is linked to C. This is what we expect if A, B and C are all on the same chromosome. We say that A, B and C are all in the same linkage group . For any species if a large number of mutations is known, the maximum number of linkage groups is the same as the haploid number.
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Genetic Recombination and Gene Mapping
We will start with a pair of mutations on the same chromosome that have will have no recombination between them. The probability that recombination occurs between two loci is directly proportional to the distance between them. So we start with two genes that are very close to each other, hv for heavy wing vein and bw for brown eye in Drosophila .
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9 Notice that we set up a cross with two heterozygous genes (in the F1 generation) and got a 1:2:1 ratio, not 9:3:3:1. The reason is linkage; hv and bw are on the same chromosome and very close to each other. They segregate together, rather than randomly, as they would if they were on different chromosomes.
Genetic Recombination

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