4.1.5 Genetic Loci

Key Features of Genetic Loci:

1. Definition:

• A locus is the precise position of a gene on a chromosome.
• Each gene has a unique locus on a specific chromosome.

2. Consistency Across Individuals:

• The locus of a gene is the same in all individuals of a species.
• For example, the gene for haemoglobin in humans is always located on the short arm of chromosome 11.

3. Alleles and Loci:

• Different forms of a gene are called alleles, and they occupy the same locus on homologous chromosomes.
• For example, the alleles for blood group (A, B, O) are found at the same locus on chromosome 9.

4. Homologous Chromosomes:

• In diploid organisms, chromosomes come in homologous pairs, so there are two loci for each gene, one on each chromosome in the pair.

5. Mutations:

• Mutations can change the sequence of DNA at a locus, potentially leading to genetic disorders or variations.