Topic 4.1 Chromosomes, genes, alleles and mutations

Question 1

4.1.1 State that eukaryote ____________ are made of DNA and proteins.

Answer 1

Eukaryote chromosomes are made of DNA and proteins.

Question 2

4.1.2 Define gene, allele and genome.

Answer 2

Gene: a region of DNA controlling a specific characteristic, corresponding to a unit of inheritance.

Allele: different variations of the same gene.

Genome: the whole of the genetic information (i.e. all the genes) of an organism

Question 3

4.1.3 Define gene mutation.

Answer 3

Gene mutation: a change to the base sequence of a gene.

Question 4

4.1.4 Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia.

Answer 4

Base substitution mutation: gene mutation caused when one base in a gene is substituted with another base.

Sickle-cell anemia

• Hb is a gene that codes for a polypeptide of 146 amino acids forming part of hemoglobin.
• Normal red blood cells:
  
  • Hb^A sequence has CTC with GAG
  • Transcribed as GAG
  • Anti-codon in translation is CUC (glutamic acid)
  • phenotype: normal red blood cells that carry oxygen efficiently but are affected by malaria
• Sickle-cell anemia red blood cells:
  
  • Hb^S sequence has CAC with GTG
  • Transcribed as GUG
  • Anti-codon in translation is CAC (valine)
  • phenotype: sickle-shaped red blood cells may carry oxygen less efficiently but have resistance to malaria

Hb^S allele causing sickle-cell anemia = more common & advantageous in countries greatly affected by malaria.