Direction: In the following questions a statement of assertion (A) is...
An allele is an alternative form of a gene one member of a pair that is located at a specific position on a specific chromosome. Diploid organisms, for example, humans, have paired homologous chromosomes in their somatic cells, and these contain two copies of each gene.
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Direction: In the following questions a statement of assertion (A) is...
Assertion: A pair of contrasting characters is termed as allele.
Reason: Only one gene of an allele is expressed in an individual.
The correct answer is option 'C' - Assertion (A) is true but reason (R) is false.
Explanation:
Alleles:
- Alleles are alternative forms of a gene that occupy the same locus (position) on a chromosome.
- They can be contrasting or different versions of the same gene.
- For example, in humans, the gene for hair color may have alleles for black hair and brown hair.
Contrasting Characters:
- Contrasting characters refer to the different forms or traits of a particular gene.
- These traits can be visible or invisible.
- For example, in the case of flower color in pea plants, the gene for flower color can have alleles for purple flowers and white flowers.
Expression of Alleles:
- Each individual has two alleles for a particular gene, one inherited from each parent.
- The expression of alleles can be dominant or recessive.
- Dominant alleles are expressed when present in either one or both copies.
- Recessive alleles are expressed only when present in both copies.
Explanation of the Assertion:
- The assertion states that a pair of contrasting characters is termed as an allele.
- This is correct because alleles are the different forms or versions of a gene that produce contrasting traits.
Explanation of the Reason:
- The reason states that only one gene of an allele is expressed in an individual.
- This is incorrect because in diploid organisms, both alleles can be expressed depending on their dominance or recessiveness.
- In the case of dominant alleles, even a single copy can lead to the expression of the trait.
- In the case of recessive alleles, both copies need to be present for the trait to be expressed.
Therefore, while the assertion is true, the reason is false as it does not provide the correct explanation for the assertion.
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