Question

Give an example to discuss the X-linked human phenotypes.

Please discuss the structure and function of telomeres and their involvement in cellular aging.

Explain how PCR amplifies a particular sequence of DNA.

Answer 1

X-linked inheritance:-

Gene causing the trait or disorder are located on X chromosome

Example for X- linked human phenotype:-

-Red Green colour blindness

- Hemophilia A

Red green colour blindness:- person cannot distinguish between shades of red and green. mainly mans are affected because it is related to X chromosome.

Structure of telomeres:- compromised of repeat sequence and bound by

Multiple telomeric interacting proteins.

Telomere DNA contains double stranded tandem repeats of TTAGGG followed by terminal 3' G-rich single stranded over hangs .

It adopt T- loop structure

Telomere end folds back on itself and 3' G strand overhang invades into double stranded DNA( forms D-Loop).

Function of telomere:-

Protect end of linear DNA molecules from deoxyribonucleases

Prevent fusion of chromosome

Replication at the end of linear DNA molecule.

#Without telomere chromosome end can fuse together and corrupt the cells genetic blueprint causing malfunction , cancer or cell death.

PCR :- technique to make many copies of specific DNA region in vitro

It relies on :- DNA polymerase

Taq polymerase

DNA primers

Steps of PCR amplified a sequence of DNA:-

#Denaturation:- 96°C heat reaction at this temperature to separate the DNA strands ,it provide single stranded template

# annealing (55°-65°C) :- cool the reaction so that primers can bind on the template

#Extension 72°C - Raise the temperature so taq polymerase extend the primer , synthesizing the new DNA strands.

This cycle is repeated 25-35 times. Takes 2-4 hours