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Where does a gene occupy a specific position on a chromosome?
Where does a gene occupy a specific position on a chromosome?
Answer
A gene occupies a specific position on a chromosome known as a locus (plural: loci). This term refers to the precise physical location of a gene or genetic marker on a chromosome, much like an address identifies a particular house on a street.
Key Aspects of Loci
- Definition: A locus is essentially the “address” of a gene on a chromosome, indicating where it is situated within the genome. Each gene has its own unique locus, and homologous chromosomes contain the same genes at corresponding loci, although they may have different alleles (variations of the gene).
- Mapping Genes: The process of determining the positions of genes along chromosomes is known as chromosome mapping. This involves creating genetic maps that reflect the relative distances between genes based on recombination frequencies observed during meiosis. Closer genes are more likely to be inherited together due to their proximity on the chromosome.
- Cytogenetic and Molecular Locations: Geneticists often describe a gene’s location using two types of maps:
- Cytogenetic location: This is based on the banding patterns visible when chromosomes are stained. For example, a gene located at “17q12” indicates it is on the long arm (q) of chromosome 17 at band 12.
- Molecular location: This provides a more precise address based on the specific sequence of DNA nucleotides that make up the chromosome
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