Question

In humans, __________ traits are much easier to identify than __________ traits. Choose the correct pair of words from the options given below for filling in the blanks :

• A. Recessive autosomal traits; X-linked traits
• B. X-linked traits; Dominant autosomal traits
• C. X-linked traits; Recessive autosomal traits
• D. Dominant autosomal traits; X-linked traits

Hint:

Because males are hemizygous for the X chromosome, recessive X-linked disorders are expressed directly in males.
This causes these disorders to be identified much more frequently in males than in females.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Inheritance patterns depend on whether genes are located on autosomes or sex chromosomes (X or Y), and whether they are dominant or recessive.
The chromosomal location of a gene determines how easily its inheritance pattern can be identified in pedigree analysis.

Step 3: Detailed Explanation:
Let us evaluate X-linked traits versus recessive autosomal traits in humans:
1. X-linked traits: Human females have two X chromosomes (\(XX\)), while males have one X and one Y chromosome (\(XY\)).
Males are hemizygous for genes on the X chromosome.
This means any allele on a male's single X chromosome will be expressed, even if it is recessive.
Recessive X-linked traits (like hemophilia or color blindness) appear much more frequently in males.
They also show a distinct "criss-cross" inheritance pattern, passing from a carrier mother to her sons. This makes them easy to identify.
2. Recessive autosomal traits: These traits require two copies of the recessive allele (\(aa\)) to be expressed.
Heterozygous individuals (\(Aa\)) do not show the trait and act as silent carriers.
These recessive alleles can remain hidden in carriers across many generations, making them difficult to identify in a population.
Therefore, X-linked traits are much easier to identify than recessive autosomal traits.

Step 4: Final Answer:
The correct pair of words to complete the sentence is "X-linked traits; Recessive autosomal traits", matching Option (C).