HW Problem _ 3 - Map distance tells you the actual % or...

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Que: If A/A • B/B is crossed to a/a • b/b, and the F1 is testcrossed, what percent of the testcross progeny  will be a/a • b/b if the two genes are  (a) unlinked;  (b) completely linked (no crossing-over at all);  (c) 10 map units apart;  (d) 24 map units apart? The cross between two homozygous parents will result in all heterozygous F1 generation (all will be  AaBb). The cross in question is AaBb x aabb (test cross is always to homozygous recessive). a), c), and d) possible gametes are AB, Ab, aB, and ab. If you do the cross (with testcross gamete ab),  you will find that when unlinked 25% will be aabb. 
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Unformatted text preview: Map distance tells you the actual % or recombinant gametes. So, if A-B is 10 m.u. apart, then 10% progeny of test cross are recombinants. That means that 90% will have parental genotype. There are 2 parental genotypes: AB and ab, each of those will occur 45% of the time (90%/2). Thus, occurrence of aabb will be 45% in this case. You can work out 24 m.u. in the same way. b) However, if genes are completely linked, then only parental genotypes are possible (AB or ab gametes) and test cross will result in 50% of each AaBb and aabb progeny....
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This note was uploaded on 01/29/2012 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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