D3.2.18 Loci of human genes and their polypeptide products (HL) Notes

Gene Loci Provide the Address of Genetic Information

1. When a mutation causies a disease, how do scientists determine which gene is responsible?
2. This is where the concept of a gene's locus becomes critical.
3. By pinpointing the exact location of a gene on a chromosome, you can uncover its role and how changes in its sequence might lead to disease.

Genes on Different Chromosomes Assort Independently

1. Genes on separate chromosomes assort independently during meiosis, following Mendel’s second law,
2. While genes close together on the same chromosome often exhibit linkage.

Databases Uncover Gene Loci and Their Functions

1. Modern genetic research relies heavily on databases like Ensembl and NCBI, which provide detailed information about gene loci and their functions.
2. To explore gene loci, follow these steps:
   1. Search for a gene (e.g., PAH, associated with PKU).
   2. Identify its locus (e.g., 12q23.2) and protein product.
   3. Use genome browsers to visualize nearby genes and study functional relationships.

Gene Loci Drive Medical and Scientific Discoveries

1. Inheritance Patterns: Linked genes affect how traits are passed on, influencing genetic counseling and predictions.
2. Genetic Disorders: Mapping loci helps diagnose and treat conditions like sickle cell anemia or cystic fibrosis.
3. Evolutionary Insights: Comparing loci across species reveals evolutionary connections and conserved functions.

Ethical Considerations Surround Gene Mapping

1. While gene mapping offers immense potential, it raises challenges:
   1. Complex Traits: Traits influenced by multiple genes and the environment are difficult to pinpoint.
   2. Privacy Concerns: Genetic data storage risks misuse or discrimination.
   3. Ethical Boundaries: Where should society draw the line in using genetic knowledge?

Genes on Different Chromosomes

1. Consider two important genes: BRCA1 and TP53.
   1. BRCA1: Located on chromosome 17 at position 17q21.31.
   2. This gene is involved in DNA repair, and mutations in BRCA1 are linked to an increased risk of breast and ovarian cancer.
   3. TP53: Found on chromosome 17 at position 17p13.1.
   4. Often called the "guardian of the genome" TP53 plays a crucial role in preventing cancer by regulating cell division and apoptosis.

Genes in Close Proximity

1. Now, let's examine genes located close together on the same chromosome.
2. For example, the HBB and HBD genes on chromosome 11:
   1. HBB: Located at 11p15.4, this gene codes for the beta-globin subunit of hemoglobin. Mutations in HBB can cause sickle cell anemia.
   2. HBD: Found nearby at 11p15.5, this gene codes for the delta-globin subunit, which is part of adult hemoglobin.

Challenges and Limitations

1. While gene mapping has advanced significantly, it is not without challenges:
   1. Complex Traits: Many traits are influenced by multiple genes and environmental factors, making it difficult to pinpoint a single locus.
   2. Genetic Variation: Single-nucleotide polymorphisms (SNPs) and other variations can complicate the identification of functional regions within a gene.
   3. Ethical Considerations: The ability to map genes raises ethical questions about privacy, genetic testing, and the potential for discrimination.