Q. 25

(a) Mention the t

Answer :


i. The traits in pea plants, where a single gene product produces more than one phenotypic effect are:

I. Size of grain (large and small)

II. Shape of grain (round and wrinkled)

ii. Effect in homozygous dominant and homozygous recessive states are:

I. Homozygous dominant (BB)- large starch grain, round seeds

II. Homozygous recessive (bb)-small starch grain, wrinkled seeds

b. The blood groups in humans are controlled by the gene I which exist in three allelic forms ‘i’, ‘IA’, and ‘IB’.Thus, it shows multiple allelism i.e., a phenomenon where a gene exists in more than two allelic forms. IA, and IB codes for glycoprotein that protrudes from the surface of the RBCs while ‘i’ does not code for anything. Therefore IA, and IB are codominant over each other i.e., two alleles of a gene are not dominant over each other and express themselves independent of the presence or absence of others while both the genes are dominant over ‘i’ i.e., the allelethat is expressed in an organism's phenotype, masking the effect of the recessive allele or gene when present.


a. Comparative study made of the fore limbs of different mammals be considered an evidence for evolution because these have similar anatomical structure despite having different functions. The forelimbs of bats, blue whale, humans are composed of humerus, radius, ulna, carpals, metacarpals, phalanges and perform different functions of flying, swimming and holding objects.

b. These are called homologous organs the same structure developed along different directions due to adaptions to different needs. Homology indicates common ancestry.

c. This is divergent evolution.

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