An allele is said to be recessive, when it is expressed ina)heterozygo...
Understanding Recessive Alleles
Recessive alleles are a fundamental concept in genetics. They play a crucial role in determining phenotypes, or observable traits, of an organism.
Definition of Recessive Alleles
- An allele is termed "recessive" when its effects are masked by the presence of a dominant allele in a heterozygous condition.
- For a recessive allele to manifest its traits, it must be present in a homozygous condition, meaning two copies of the recessive allele are required.
Homozygous vs. Heterozygous Conditions
- Homozygous Condition:
- An organism possesses two identical alleles for a particular gene (e.g., aa).
- The recessive trait is expressed when both alleles are recessive.
- Heterozygous Condition:
- An organism carries one dominant and one recessive allele (e.g., Aa).
- The dominant allele will overshadow the recessive allele, preventing its expression.
Expression of Recessive Traits
- A recessive trait is only observable in the homozygous condition.
- Therefore, the correct answer to the original question is option 'B', as recessive alleles are expressed only when an individual has two copies of that allele.
Conclusion
Understanding the interaction between dominant and recessive alleles is essential for predicting inheritance patterns in genetics. Recessive traits require a specific genetic configuration (homozygous) to be expressed, distinguishing them from dominant traits, which can manifest even in a single copy.
An allele is said to be recessive, when it is expressed ina)heterozygo...
The factor of an allelic or allelomorphic pair which is unable to express its effect in the presence of its contrasting factor in a heterozygote is called recessive factor or allele, e.g., the allele ′t′ in hybrid tall pea plant Tt. The effect of recessive factor becomes known only when it is present in the pure or homozygous state, e.g., tt in dwarf pea plant.