Question

Write a note on the following :
(i) Genetic Code
(ii) Sex - determination in human.

Answer 1

(i) Genetic code:

It is defined as the sequence of nitrogenous bases on mRNA or DNA which specifies the sequence of amino acids in the polypeptide chain.

Features of genetic code are-

1. The genetic code is written in a linear form with the letters of nitrogenous bases.

2. Each word of a codon consists of three letters, therefore the codon is a triplet. So, an amino acid is specified by three nitrogenous bases in RNA or DNA.

3. The genetic code is non-ambiguous and specific because of each codon codes for one amino acid only.

4. The genetic code is degenerate because each amino acid may be specified by more than one codons.

5. AUG codes for methionine and is also called as the start codon.

6. There are three stop codons UGA, UAA and UAG.

7. The code is universal with some exceptions

(ii) Sex determination in human:

In humans, sex determination is by the XX-XY pattern. The females possess two homomorphic X chromosomes i.e. XX. So they are homogametic and produces eggs of only one kind all of which have one X chromosome in them. The males possess one X chromosome and one Y chromosome. So they are heterogametic and produces two kinds of sperms, 50% having X chromosome and 50% having a Y chromosome.