A particular variety of corn has a gene for kernel color and a gene for height w
ID: 18566 • Letter: A
Question
A particular variety of corn has a gene for kernel color and a gene for height with thefollowing phenotypes:
CC, Cc; purple kernels
cc; white kernels
TT, Tt; Tall stems
tt; dwarf stems
Two true breeding plants are crossed; one is true breeding for purple kernels and dwarf stems, and the other is true breeding for white kernels and tall stems. The F1 offspring all have purple kernels and tall stems. Two of these F1 plants are then crossed.
(a) Diagram a Punnett square showing the cross between the two F2 plants. In each square, indicate the phenotype of that genotype. Indicate the ratios of the phenotypes and the genotypes.
(b) You are given one of the F2 plants that has purple kernels and tall stems. You want to determine what the genotype of this plant is, so you perform a testcross. What will be the genotype and phenotype of the test plant? Why?
(c) If you perform the test cross in part c and the F2 plant is heterozygous for purple kernels and homozygous for tall stems, predict the genotypic and phenotypic ratio of the test-cross offspring.
Explanation / Answer
a) F1 generation = CcTt
F1 Generation cross = CcTt xCcTt
CT Ct cT ct
CT CCTT CCTt CcTt CcTt
Ct CCTt CCtt CcTt Cctt
cT CcTT CcTt ccTT ccTt
ct CcTt Cctt ccTt cctt
CcTt = 5/16 CCtt = 1/16 CCTT = 1/16
CCTt = 2/16 CcTT = 1/16 Cctt = 2/16
ccTT = 1/16 ccTt = 2/16 cctt = 1/16
b) cctt, will be the test plant crossed with the purple/tall plant. This way you can rule out by ratios of the progeny whether the parent (purple/tall) is a homozygous or heterozygous
c) CcTT x cctt
CT CT cT cT
ct CcTt CcTt ccTt ccTt CcTt = 50% ccTt = 50%
ct CcTt CcTt ccTt ccTt
ct CcTt CcTt ccTt ccTt
ct CcTt CcTt ccTt ccTt
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