2004 AIPMT Molecular Basis of InheritanceDNA Packaging and Chromosome Ends Medium Question 163 of 200 in Molecular Basis of Inheritance

The telomeres of eukaryotic chromosomes consist of short sequences of -

A Cytosine rich repeats
B Adenine rich repeats
C Guanine rich repeats
D Thymine rich repeats

The answer is C.

Solution

Telomeres are the protective ends of linear eukaryotic chromosomes.
They consist of many tandem repeats of a short DNA sequence. In humans and other vertebrates the repeat is TTAGGG, on the strand running 5' to 3' towards the end of the chromosome.
This strand is rich in guanine (three G in every six bases), and it forms a single-stranded G-rich overhang at the 3' end. Similar G-rich repeats occur in other eukaryotes (e.g. TTGGGG in Tetrahymena).
The enzyme telomerase, which carries its own RNA template, adds these G-rich repeats to the chromosome ends to prevent shortening at each replication.
So telomeres consist of short sequences of guanine rich repeats.

Concept G-rich telomeric repeats

Molecular Basis of Inheritance in past papers

200 questions from this chapter have appeared across 27 exam years.