(a) Write the features a molecule should have to act as a genetic material. In the light of the above features, evaluate and justify the suitability…

-It should be able to generate its replica.

-Be chemically and structurally stable.

-Provide scope for slow changes(mutation) required for evolution.

-Able to express itself in the form of ‘Mendelian Characters’.

DNA is double-stranded whereas RNA is single-stranded, DNA has thymine instead of uracil which is present in RNA and thus DNA is more stable, DNA has $\displaystyle 2$’-H group whereas RNA has $\displaystyle 2$’-OH group at every nucleotide which is reactive and easily degrades RNA, RNA is also catalytic, both RNA and DNA can mutate but RNA mutates faster than DNA.

Based on above points DNA molecule is preferred as an ideal genetic material .

Polygenic Inheritance-Inheritance of a trait that is controlled by three or more genes / the phenotype reflects contribution of all alleles (three or more) and effect of each allele is additive.

Pleiotropy – When a single gene shows multiple phenotypic expressions.

Dominance – In heterozygous pair of gene dominant allele is expressed over the recessive allele/ F1 progeny resemble either of the two parents which is dominant.

Codominance – In a pair of genes when both alleles express themselves/ F1 generation(one of the progeny) resembles both the parents.

Incomplete dominance – When in heterozygous state none of the allele is able to express itself and phenotype is in between/ Phenotype of F1 progeny is in between the two parent.