35. A gene inherited from mother is not expressed the offspring, but the same gene when inherited from father is expressed in both male and female offspring. This phenomenon is the hallmark of gene
(1) recombination    (2) deletion
(3) silencing             (4) imprinting

Gene inheritance patterns can show unique phenomena where a gene inherited from the mother is not expressed in offspring, but the same gene inherited from the father is actively expressed. This phenomenon is a hallmark of genetic imprinting.

Explanation of Genetic Imprinting and Other Options

• Genetic Imprinting: This refers to an epigenetic phenomenon where only one allele of a gene is expressed depending on whether it is inherited from the mother or the father. The other allele is silenced by chemical modifications such as DNA methylation during gamete formation. For example, if the maternal allele is imprinted (silenced), only the paternal allele is expressed in the offspring. This parent-of-origin specific gene expression is essential in mammalian development and differs from normal Mendelian inheritance where both alleles are typically expressed equally.

• Gene Recombination: This involves the exchange of genetic material between homologous chromosomes during meiosis, resulting in new allele combinations in offspring. Recombination increases genetic diversity but does not cause parent-specific gene expression or silencing. It is more about shuffling genes than selectively expressing one parent’s allele.

• Deletion: This is a mutation where a segment of DNA is lost or deleted from the chromosome. It causes loss of genetic material but is not related to selective expression of parental alleles.

• Silencing: Broadly refers to the inactivation of gene expression, often by epigenetic mechanisms. However, silencing alone does not specify imprinting unless it is parent-specific and stable across generations. General gene silencing can occur due to other reasons like RNA interference, but it does not necessarily involve imprinting.

Summary

The key feature described in the question—where a gene inherited from the mother is not expressed, but the gene inherited from the father is expressed in offspring—is the hallmark of genetic imprinting. This distinguishes imprinting from recombination, deletion, and generic silencing.

This detailed explanation clarifies that the correct answer to the question is option (4) genetic imprinting, a special form of gene expression regulation depending on the parental origin of the gene.​

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