Lecture 17 - Relationship between Genes and Phenotype

Question 1

Error in DNA sequence can be repaired trough three methods. Mention all of them.

Answer 1

Proofreading (during DNA replication), Excision repair and Mismatch repair (after DNA replication)

Question 2

What is PCR? Explain its mechanism.

Answer 2

Polymerase chain reaction is a method that mimics DNA replication, which can amplify DNA regions to substantial amounts. First, the sample DNA is separated by heating it up to 95 C. DNA primers are annealed at 60-65 C. New bases are added to the templated by the Taq polymerase.

Question 3

Taq polymerase is the type of DNA polymerase used in PCR techniques. It is derived from the prokaryote ________.

Answer 3

Thermus aquaticus

Question 4

Alkaptonuria is caused by the build-up of ________, characterized by the urine turning black in contact with air.

Answer 4

Homogentisic acid.

Question 5

Differ between a prototroph and auxotroph.

Answer 5

Prototroph: grows on minimal media

Auxotroph: requires a supplement in the medium

Question 6

Explain the conclusion that Beadle and Tatum made from their experiment. How has that conclusion been modified over time?

Answer 6

The conclusion they arise to is that a gene can code for an enzyme.

This is modified to a gene codes for a protein (as collagen and fibrin are non-enzyme inherited traits).

This is later modified to a gene codes for a polypeptide (as some proteins are made up of subunits that are encoded by different genes).

Some genes are later found to only code for RNA not polypeptides.

Question 7

Give three examples of diseases caused by a mutation in genes which coded for enzymes resulting in a block in a biochemical pathway.

Answer 7

Alkaptonuria, Dwarfism, Albinism, Phenylketonuria