[A] : Sensescence in the time when age as- sociated defects are manifested.
[R]: Certain genes may be undergoing se- quential switching on & off during one s life.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark a
B. lf both Assertion & Reason are true but the reason is no t the correct explanation of the assertion, then mark b
C. If Assertion is true statement but Reason is false, then mark c
D. If both Assertion and Reason are false statements, then mark d.

Answer

A

Explanation

Process of ageing is called senscence. A geing, is cumulative changes in an organism, organ tissue, or cell leading to decrease in functional capacity. In humans, geing is associated with degenerative changes in the skin, bones, heart, blood vessels, lungs, nerves, and other organs and tissues.
It is genetically controlled programme regulated by regulatory genes. This view is suggested by the great range of lifespans among different animal species-from a few days in the fruit fly to more than 100 years in some tortoises. Scientists have recently learned how to double the lifespans of such laboratory organisms as roundworms and fruit flies through genetic manipulation, and mutant genes in mice have been observed to have a comparable effect in postponing ageing. Genes which have deleterious effect on individual's fitness are selected against by natural selection. Mutations in these genes which postponed the deleterious effect of the gene to a later time in individual's life history reduce the effect of natural selection to the gene, because the selection has less time to act on to. If the gene doesn't have a negative effect until after the individual has reproduced, the gene may escape natural selection altogether, because when selection starts to affect the gene, it has already propagated to the next generation. In a related fashion, some genes may help to ensure reproduction at the cost of diseases later in life. For instance, our immune system generally helps to keep us healthy during reproductive age, but many adults acquire autoimmune diseases such as rhemuatoid arthritis as they age.