. In corn (Zea mays), a dominant gene c+ produces colored kernels and its recess

Question

. In corn (Zea mays), a dominant gene c+ produces colored kernels and its recessive allele (c) produces colorless kernels. Another dominant gene, sh+, produces full kernels while its recessive allele, sh, produces shrunken kernels. Waxy endosperm is controlled by a recessive gene, wx, while normal endosperm is produced by wx+. A testcross between a triply heterozygouse plant and a shrunken, colorless, waxy plant produces the following progeny:
phenotype phenotype (allele) # offspring
c sh+ wx 125
c sh wx 18
c+ sh+ wx 72
c sh wx+ 68
c+ sh wx 300
c+ sh+ wx+ 22
c+ sh wx+ 115
c sh+ wx+ 280

Draw a genetic map for the chromosomes including the gene order and map distances.

Explanation / Answer

The parental gametes are:
colorless, waxy, plump c wx Sh
colored, nonwaxy, shrunken C Wx sh

The double recombinant gametes are:
colorless, waxy, shrunken c wx sh
colored, nonwaxy, plump CWx Sh

The gene for endosperm size (Sh) is the gene in the middle, so
the order of the genes is either
C Sh Wx or Wx Sh C

The distance between genes C and Sh is:
72 + 68+18+ 22 = 180/1000 = 0.180 x 100 =
18 map units

The distance between genes Sh and Wx is:
125+ 115 + 18+ 22 = 1280/1000 = 0.280 x 100 =
28 map units

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