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VALENCIA BSC 1005 - AL#2 Testcross Key

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Slide 1AL Exercise #2: Three-Point Testcross ActivityA 3-point testcross was conducted to determine the order and map distance between three linked genes aristaless antennae (al), brown eyes (bw), and vestigial wings (v) – not necessarily in this order - located on chromosome 2 in Drosophila. A homozygous wild type fly was crossed to an aristaless, brown, and vestigial fly. The resulting heterozygous F1 females of this cross were testcrossed and produced 500 F2 progeny that fall into the phenotypic classes below.F1 Testcross: ----------------- X -----------------F2 Phenotype Number Genotype SCO, DCO, nonrecombinant?wild type 205 -----------------aristaless brown vestigial 200 -----------------brown vestigial 36 -----------------aristaless 34 -----------------brown 11 -----------------aristaless vestigial 9 -----------------aristaless brown 3 -----------------vestigial 2 -----------------A)Determine the linear order of the genes based on the types and numbers of F2 progeny.B)Determine the distances between the 3 linked genes:-Write out the genotype of each F1 parent in the testcross and each F2 progeny class.-Label each progeny class as resulting from a single-crossover (SCO), double-crossover (DCO) or no recombination.-Indicate with a hash mark the location of each SCO and DCO on recombinant chromosomes.-Calculate the recombination frequency for each pair of genes, and convert to map units.C)Answer questions on next page.al - vv -


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