4.1 Chromosomes, Genes, and Alleles
1. State: Eukaryotic chromosome is made of DNA and protein.
2. Define: gene, allele, and genome.
- gene = a heritable factor that controls a specific characteristic
- allele = one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene
- genome = the whole of the genetic information of an organism
3. Define: a gene mutation is a change in the base sequence of a gene.
4. Explain the consequence of a base substitution mutation in relation to the process of transcription and translation, using the example of sickle cell anemia.
- Base substitution: the replacement of one (or more) DNA base(s) with another
- because of the redundancy of the genetic code, some substitutions will have no effect on the amino acid sequence coded for by the gene
- where the substitution does have an effect, it may produce either missense, altering a single amino acid, or nonsense, introducing a new stop codon
- Sickle cell anemia: substitution in gene for ß chain of hemoglobin
- base substitution changes DNA sequence: CTC → CAC
- altering the mRNA transcript: GAG → GUG
- altering a single amino acid in beta hemoglobin: glutamic acid → valine
- changing the nature of beta hemoglobin
- sickle cell anemia: two mutant allele copies
- with two sickle cell alleles, RBCs sickle under low oxygen conditions
normal sickle cell mutation
DNA CTC CAC
mRNA GAG GUG
amino acid glutamic acid valine
4.2 Lecture Notes