1. Topic 4.1 - Chromosomes, Genes, Alleles and Mutations
4.1.1. State that eukaryote chromosomes are made of DNA and proteins.
4.1.2. Define gene, allele, and genome.
• A gene is a heritable factor that controls a specific characteristic.
• An allele is 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.
• A genome is the whole of the genetic information of an organism.
4.1.3. Define gene mutation.
• A gene mutation is a change in the base sequence of the DNA in a gene that ultimately creates
genetic diversity.
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.
• A base substitution is the replacement of one nucleotide and its partner from the complementary
DNA strand with another pair of nucleotides.
• In sickle cell anemia, GAG (codes for glutamic acid) mutates to GTG (codes for valine).
• This places the different amino acid on the polypeptide during translation.
• Therefore, the resulting protein is mutated and normal hemoglobin is replaced by sickle-cell
hemoglobin.
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