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NEETZoologyPrinciples of Inheritance and Variation

In a genetic cross, a dihybrid organism with genotype AaBb is test crossed with a double recessive individual (aabb). If the dominant alleles A and B are completely linked on one chromosome, and the recessive alleles a and b are completely linked on its homologue (with no crossing over), what will be the expected phenotypic ratio in the progeny?

Options

  1. A1 : 1 : 1 : 1
  2. B9 : 3 : 3 : 1
  3. C1 : 1
  4. D3 : 1

Correct answer

C. 1 : 1

Step-by-step solution

In a typical dihybrid test cross involving independent assortment, the expected phenotypic ratio is 1 : 1 : 1 : 1. However, in this scenario, the genes are completely linked. The dihybrid parent (AaBb) has alleles A and B linked on one chromosome, and a and b linked on the homologous chromosome. Because there is no crossing over, this parent will produce only two types of gametes: AB and ab, in equal proportions. The double recessive parent (aabb) produces only one type of gamete: ab. When these gametes fuse, the r

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