Question

Given below are two statements:
Statement I : When two dominant alleles of two different genes are present in a chromosome and corresponding recessive alleles are present in the other homologue, this is called cis-heterozygote
Statement II : When two dominant alleles of two different genes are present in both the homologous chromosomes in homozygous condition, this is called cis-heterozygote
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is correct but Statement II is false
• D. Statement I is incorrect but Statement II is true

Hint:

Cis-heterozygote (coupling) $= AB/ab$; Trans-heterozygote (repulsion) $= Ab/aB$; $AB/AB$ is a homozygote.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
William Bateson and Reginald Punnett distinguished coupling (cis) and repulsion (trans) linkage arrangements in double heterozygotes.

Step 2: Detailed Explanation:
1. Statement I is TRUE: In a dihybrid heterozygote, when both dominant alleles are linked on one homologous chromosome and both recessive alleles on the other ($AB / ab$), it is termed the cis-heterozygote (coupling phase).
2. Statement II is FALSE: When both dominant alleles are present on both homologues in homozygous condition ($AB / AB$), the individual is a double homozygote, not a heterozygote.

Step 3: Final Answer:
Hence, Statement I is correct but Statement II is false.