Assertion (A): The characteristics (or traits) of an organism are determined by ‘internal factors’ (now called ‘genes’) which occur in pairs. Only one of a pair of such ‘factors’ can be present in a single gamete. Reason (R): The genes which dominate other genes are called dominant genes and the genes which get dominated are called recessive genes.

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Both A and R are true but R is not the correct explanation of the assertion. Explanation: The characteristics (traits) of an organism are determined by genes, which occur in pairs. During the formation of gametes, the paired genes segregate, so that each gamete receives only one gene from the pair. Therefore, Assertion (A) is true. Dominant genes express their effect even in the presence of a recessive gene, whereas recessive genes express their effect only in the absence of a dominant gene. Therefore, Reason (R) is true. However, Reason (R) does not explain why only one gene of a pair is present in each gamete. This is explained by Mendel’s Law of Segregation. Hence, both A and R are true but R is not the correct explanation of the assertion.

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