True-breeding red-eyed Drosophila flies with plain thoraxes were crossed with pink-eyed flies with striped thoraxes. Red-eye and plain thorax X P i n k- e y e and striped thorax The F 1 flies were then test crossed against the double recessive. The following F2 generation resulted from the cross: 80 16 12 92 Red-eye Red-eye Pink-eye Pink-eye Plain thorax Striped thorax Plain thorax Striped thorax What percentage number of recombinants resulted from the testcross?

Question

True-breeding red-eyed Drosophila flies with plain thoraxes were crossed with pink-eyed flies with striped thoraxes. Red-eye and plain thorax X P i n k- e y e and striped thorax The F 1 flies were then test crossed against the double recessive. The following F2 generation resulted from the cross: 80 16 12 92 Red-eye Red-eye Pink-eye Pink-eye Plain thorax Striped thorax Plain thorax Striped thorax What percentage number of recombinants resulted from the testcross?, 12, 14, 16, 28

MARKS App · Accepted Answer

A test cross is a process to examine and identify whether the organism is heterozygous or not. In it, the organisms are crossed with the recessive homozygous as it will ensure the expression of the dominant character in heterozygous form for F 1 generation enabling us to know the zygosity. A test cross is a type of back cross. The total number of offsprings: 80 + 92 + 16 + 12 = 200 Recombinants are those which have a combination other than parents. F 1 is a hybrid having phenotype - Red eye and the plain thorax. Recessive parent - Pink eye striped thorax. Total recombinants - Red eye stripe thorax and Pink eye plain thorax: 16 + 12 = 28 Percentage of recombinants in the F 1 of testcross = T o t a l n u m b e r o f r e c o m b i n a n t s T o t a l n u m b e r o f p r o g e n y x 100 = 28 200 x 100 = 14 %

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80	16	12	92
Red-eye	Red-eye	Pink-eye	Pink-eye
Plain thorax	Striped thorax	Plain thorax	Striped thorax