particular species of tomato plant, the plants can bear fruits of different colo

Question

particular species of tomato plant, the plants can bear fruits of different colors. Suppose a researcher rosses a homozygous plant that bears white fruit with a different stock of homozygous plant that also bears white fruit. In the F1 generation, all of the fruits are red. Two F1 plants are then crossed and the F2 progeny are examined. The F2 generation contains 331 plants with red fruit and 258 with white fruit. What are the genotypes of the F2 progeny? Fruit color Genotypes red A B white What type of epistasis, if any, is present? duplicate recessive epistasis O O recessive epistasis O no epistasis O dominant epistasis O duplicate dominant epistasis

Explanation / Answer

Answer: The genotype of F2 generation are aaBB, aaBb, AAbb, Aabb and aabb.

The normal ratio from selfing dihybrid is 9:3:3:1, but here in above case the ratio of red colored fruit to white colored fruit is 9:7. This is a classic example of duplicate recessive epistasis.When both gene loci have homozygous recessive alleles and both of them produce identical phenotype then the F2 ratio 9:3:3:1 would be 9:7. Recessive alleles at either of the two loci can mask the expression of dominant alleles at the two loci, it is called duplicate recessive epistasis. Both dominant alleles when are present together only then they can complement each other. Thats why its also known as complementary epistasis.

  

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