Question

A gene is said to be dominant if :-

• A. It expresses it's effect only in homozygous state
• B. It expresses it's effect only in heterozygous condition
• C. It expresses it's effect both in homozygous I and heterozygous condition.
• D. It never expresses it's effect in any condition.

Answer 1

The Correct Option is C

To understand the concept of dominance in genetics, let's clarify what a dominant gene is. A gene is considered dominant when it is expressed in the phenotype even if only one allele of the gene is present. Alleles are different versions of a gene, and they can be dominant or recessive. Let's explore each option and why the given answer is correct:

1. Option 1: It expresses its effect only in homozygous state.
   This option describes a recessive gene. A recessive gene's effects are only seen when both alleles are recessive (homozygous recessive), not in the case of a dominant gene.
2. Option 2: It expresses its effect only in heterozygous condition.
   This description is incorrect for a dominant gene because a dominant gene's traits are expressed both in heterozygous and homozygous conditions.
3. Option 3: It expresses its effect both in homozygous and heterozygous condition.
   This is the correct description of a dominant gene. A dominant gene will control the trait in both homozygous dominant (having two dominant alleles) and heterozygous (having one dominant and one recessive allele) states.
4. Option 4: It never expresses its effect in any condition.
   This option contradicts the basic definition of a gene. A gene is a segment of DNA which influences certain traits, so it must express its effect under specific conditions.

Therefore, the correct answer is "It expresses its effect both in homozygous and heterozygous condition," as this describes a dominant gene. A real-world example would be the inheritance of brown eyes over blue eyes due to the dominance of brown eye alleles.