Q14.2 In the Chinese primrose, slate-colored flower (s) is recessive to blue flo
ID: 101105 • Letter: Q
Question
Q14.2 In the Chinese primrose, slate-colored flower (s) is recessive to blue flower (S), red stigma (r) is recessive to green stigma (R), and long style (l) is recessive to short style (L). All three genes involved are on the same chro- mosome. The F1 of a cross between two true-breeding strains, when testcrossed, gave the following progeny:
Phenotype
Number of Progeny
slate flower, green stigma, short style 27
slate flower, red stigma, short style 85
blue flower, red stigma, short style 402
slate flower, red stigma, long style 977
slate flower, green stigma, long style 427
blue flower, green stigma, long style 95
blue flower, green stigma, short style 960
blue flower, red stigma, long style 27
Total 3,000
a. What were the genotypes of the parents in the cross of the two true-breeding strains?
b. Make a map of these genes, showing their order and the distances between them.
c. Derive the coefficient of coincidence for interference between the given genes.
Explanation / Answer
Ans.) As the information provided, the F1 cross is between SRL / srl and all the 3 genes for flower color, stigma and style are located on the same chromosome. The total progeny are 3000 with different phenotypic character like
Slate flower, green stigma, short style = 27
Slate flower, red stigma, short style = 85
Blue flower, red stigma, short style = 402
Slate flower, red stigma, long style = 977
Slate flower, green stigma, long style = 427
Blue flower, green stigma, long style = 95
Blue flower, green stigma, short style = 960
Blue flower, red stigma, long style = 27
a.) The genotypes of the parents in the cross of the two true-breeding strains would be
SSrrLL x ssRRll
b). The different recombinant classes of these progenies --
If RS recombinants are Rsl and rSL - Green slate long (427) and red blue short (402)
Percent recombination = (no. of recombinants/total no. of offspring) x 100%
= ((402 + 427 + 27 +27)/3000) x 100% = 29.4%
If SL recombinants are RSl and rsL - green blue long (95) and red slate short (85)
Percent recombination = ((85 + 95 + 27 +27)/3000) x 100% = 7.8%
Finally RL, percent recombination = ((402 + 427 + 85 + 95)/3000) x 100% = 33.6%
The percent recombination is equal to the distance between genes in map units (cM centimorgans), so map of these genes will be --
R ------------ ------ S ----- -- L
c). Coefficient of coincidence = Actual double recombinant frequency / Expected double recombinant frequency Hence, the coefficient of coincidence = 0.78
Ans.) As the information provided, the F1 cross is between SRL / srl and all the 3 genes for flower color, stigma and style are located on the same chromosome. The total progeny are 3000 with different phenotypic character like
Slate flower, green stigma, short style = 27
Slate flower, red stigma, short style = 85
Blue flower, red stigma, short style = 402
Slate flower, red stigma, long style = 977
Slate flower, green stigma, long style = 427
Blue flower, green stigma, long style = 95
Blue flower, green stigma, short style = 960
Blue flower, red stigma, long style = 27
a.) The genotypes of the parents in the cross of the two true-breeding strains would be
SSrrLL x ssRRll
b). The different recombinant classes of these progenies --
If RS recombinants are Rsl and rSL - Green slate long (427) and red blue short (402)
Percent recombination = (no. of recombinants/total no. of offspring) x 100%
= ((402 + 427 + 27 +27)/3000) x 100% = 29.4%
If SL recombinants are RSl and rsL - green blue long (95) and red slate short (85)
Percent recombination = ((85 + 95 + 27 +27)/3000) x 100% = 7.8%
Finally RL, percent recombination = ((402 + 427 + 85 + 95)/3000) x 100% = 33.6%
The percent recombination is equal to the distance between genes in map units (cM centimorgans), so map of these genes will be --
R ------------ ------ S ----- -- L
c). Coefficient of coincidence = Actual double recombinant frequency / Expected double recombinant frequency
Hence, the coefficient of coincidence = 0.78
and Interference = 1- coefficient of coincidence = 0.22
and Interference = 1- coefficient of coincidence = 0.22
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