7.3 Gene Linkage and Mapping KEY CONCEPT Genes can be mapped to specific locations on chromosomes.

7.3 Gene Linkage and Mapping Gene linkage was explained through fruit flies. Thomas Hunt Morgan found that linked traits are on the same chromosome and can be inherited together. Chromosomes, not genes, assort independently during meiosis. Wild type Mutant Fig. 3.1 – The wild type fruit fly shows the most common phenotype. The mutant fruit fly has white eyes, no wings and a different body color.

7.3 Gene Linkage and Mapping Because the linked genes were not inherited together every time, Morgan also concluded that chromosomes must exchange homologous genes during meiosis (crossing over).

7.3 Gene Linkage and Mapping Linkage maps estimate distances between genes. The closer together two genes are, the more likely they will be inherited together. Cross-over frequencies are related to distances between genes. Linkage maps show the relative locations of genes.

7.3 Gene Linkage and Mapping Linkage maps estimate distances between genes. Summarize: How can a linkage map be made from observations of traits?

7.3 Gene Linkage and Mapping Cross-over frequencies can be converted into map units. The order of genes on a chromosome can be determined if all of their cross-over frequencies are known. – gene A and gene B cross over 6.0 percent of the time – gene B and gene C cross over 12.5 percent of the time – gene A and gene C cross over 18.5 percent of the time A = body color B = eye color C = wing size

7.3 Gene Linkage and Mapping 1.Based on the above linkage map, what is the frequency that gene A and gene B cross over together? Gene D and gene C? 2.Draw a linkage map based on the following cross-over percentages for three gene pairs: A-B = 8%, B-C = 10% and A-C = 2%