A test cross between a plant of genotype PpSs and the tester of genotype ppss gi

Question

A test cross between a plant of genotype PpSs and the tester of genotype ppss gives the following numbers of progeny in four phenotypic types. 14:86:84:16 (purple flower + smooth seed coat: purple flower + wrinkled seed coat: white flower + smooth seed coat: white flower + wrinkled seed coat). a) What is the expected ratio of progeny phenotypes assuming independent assortment of alleles? b) Explain how ratios of progeny show that the two genes are linked. c) How many map units separate the purple and smooth genes? Show your calculations.
A test cross between a plant of genotype PpSs and the tester of genotype ppss gives the following numbers of progeny in four phenotypic types. 14:86:84:16 (purple flower + smooth seed coat: purple flower + wrinkled seed coat: white flower + smooth seed coat: white flower + wrinkled seed coat). a) What is the expected ratio of progeny phenotypes assuming independent assortment of alleles? b) Explain how ratios of progeny show that the two genes are linked. c) How many map units separate the purple and smooth genes? Show your calculations.
A test cross between a plant of genotype PpSs and the tester of genotype ppss gives the following numbers of progeny in four phenotypic types. 14:86:84:16 (purple flower + smooth seed coat: purple flower + wrinkled seed coat: white flower + smooth seed coat: white flower + wrinkled seed coat). a) What is the expected ratio of progeny phenotypes assuming independent assortment of alleles? b) Explain how ratios of progeny show that the two genes are linked. c) How many map units separate the purple and smooth genes? Show your calculations.

Explanation / Answer

Answer

a). Dihybrid test cross phenotypic ratio when alleles assort independently is 1:1:1:1

PpSs. X. ppss

So the ratio is 50:50:50:50

b).

Wrinkled seeds and purple flowers (86) and smooth seeds and white flowers (84) are parental phenotypes. Total parental phenotypes are 170

Recombinant phenotypes are smooth seeds and purple flowers (16) and wrinkled seeds and white flowers (16). Total recombinants are 30.

C). Recombination frequency =( number of recombinants/total progeny) 100

= (30/200) 100

= 15%

(%) of recommendation frequency =map unit distance

15 map units separate the purple and smooth genes.

ps PS PpSs Ps Ppss pS ppSs ps ppss

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