Three point linkage analysis Below are the data for three linked genes, brown ey

Question

Three point linkage analysis Below are the data for three linked genes, brown eyes (BW), curved wings (C), black body. All three genes are recessive. Which gene is in the middle of the linkage group? Results of Cross #1 PO Parents (Female: CiBW,BL) x (Male: F1 Offspring Phenotype Number Proportion Ratio Female: 4961 0.5005 1.002 Male: 4951 0.4995 1.000 Total 9912 Results of Cross #2 Ignoring Sex F1 Test Cross (Female: x (Male: C,BW;BL) F2 Offspring Phenotype Number Proportion Ratio 3138 0.3146 13824 BW 870 0.0872 3.833 227 0.0228 1.000 789 0.0791 3.476 BW:C BL 789 0.0791 3.476 BW BL 249 0.0250 1.097 C:BL 874 0.0876 3.850 C:BW BL. 3038 0.3046 13.383

Explanation / Answer

The No crossing over type always has highest progeny Number, thus +++ (3138) and BL BW C (3038) are the two  No crossing over type progeny.

The Duoble crossing over type always has lowest progeny Number, thus ++C (227) and BL BW + (249) are the two  No crossing over type progeny.

Thus, the allele which is changed form +++ (No crossing over type) to ++C (Duoble crossing over type) is the Curved wings C allele. This possible in Duoble crossing over type only when it located at the middle between other two allele.

So, the Sequence of 3 allele are-- BL C BW or BW C BL....

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