Alleles
- A gene codes for a specific polypeptide that can affect a specific trait or characteristic in an organism
- Eg. blood type
- Alternative forms of a gene can exist, these various specific forms are called alleles
- Note that although alleles are different forms of the same gene, they all still occupy the same locus on the chromosome
- New alleles occur through mutations
- Multiple alleles can exist for a gene that determines a specific trait
- Each allele results in a different variation of that trait
- Eg. blood types A, B, AB and O
- Each allele results in a different variation of that trait
- The chromosomes of eukaryotic cells occur in homologous pairs (there are two copies of each chromosome, one copy inherited from each parent) which means that cells have two copies of every gene
- As a result, a cell possesses two alleles of every gene within its nucleus
- When the two alleles at a locus are the same/identical they are described as homozygous
- When the two alleles at a locus are different they are described as heterozygous
Chromosomes showing genes, loci and alleles