CBSE Class 10 Science 2022 · Paper 31(B)/6 · Question 3(a)

DNA (deoxyribonucleic acid) is the chemical present in the chromosomes in the nucleus of a cell that carries the information for the inheritance of features from parents to the next generation; it is the information source for making proteins. Reason: during reproduction a cell builds a copy of its DNA by chemical reactions, and no biochemical reaction is absolutely reliable. So some small changes (variations) creep in each time DNA is copied, and the copies formed are similar to each other but may not be identical to the original DNA. (A copy with a drastic change cannot work with the cell's apparatus and the new cell dies; cells whose copies carry small changes survive, and this gives variation.)