Sickle cell Anaemia is an example of which type of chromosomal defect?

Explanation

Option [A] chromosomal rearrangement includes inversions,reciprocal translocations that can have effect on gene expression through positive effectsOption [B] Transposition of gene is the change in gene position.Option [C] chromosomal aberrations are the mega changes which involve presence of an extra chromosome or loss of chromosome from diploid number of chromosomes.Option [D] In Sickle cell anaemia,the 6th amino acid[ glutamic acid] is replaced by another amino acid [valine] in each haemoglobin BETA chain so haemoglobin is unable to carry out its normal function of carrying oxygen [haemoglobin becomes abnormal].In the nucleotide order,the nitrogenous base thymine is replaced by adenine.Since there is alterations in the sequence of DNA nucleotide so it is an example of POINT MUTATION [If alterations involve one or a few base pairs in the coding sequence they are called point mutation]. Hence option D is right.