4.1 Chromosomes, Genes, Alleles and Mutations

Question 1

Describe the structure of eukaryotic chromosomes

Answer 1

Eukaryotic chromosomes consist of DNA wrapped around histone proteins

Question 2

Define gene

Answer 2

A heritable factor that controls a specific characteristic

Question 3

Define allele

Answer 3

A specific form of a gene, occupying the same locus as other alleles of the gene

Question 4

Define genome

Answer 4

The whole of the genetic information of an organism

Question 5

Define gene mutation

Answer 5

A change in the nucleotide sequence of a gene

Question 6

Define base substitution mutation

Answer 6

The change of a single base in a sequence of DNA, resulting in a change to a single mRNA codon during transcription

Question 7

Describe and explain the effects of sickle-cell anaemia as an example of a base substitution mutation

Answer 7

• Sickle cell anaemia is inherited and cannot be passed on through infection
  
  • Affected gene found on chromosome 11
  • A base substitution mutation changes GAG to GTG causing glutamic acid to be replaced by valine
  • The resulting amino acid change alters the shape of the haemoglobin, causing it to form fibrous, insoluble strands
  • As a result, the haemoglobin are a lot less efficient at transporting oxygen, causing anaemia

Question 8

State and explain the relationship between malaria rampancy and sickle-cell anaemia rates

Answer 8

• In areas where malaria is rampant, sickle cell anaemia is more common because the malaria parasite cannot infect the mutated haemoglobin
  
  • Thus sickle cell anaemia gives carriers an advantage