Gene Mapping by Somatic Cell Hybridization

Introduction

Gene mapping is a technique used to locate genes on specific chromosomes. Somatic cell hybridization is a powerful method for gene mapping, particularly for humans and other species where traditional breeding methods are impractical. This method involves the fusion of somatic cells from different species to study chromosome behavior and assign genes to specific chromosomes.

Principle of Somatic Cell Hybridization

In somatic cell hybridization, cells from two different species (e.g., human and mouse) are fused to form a heterokaryon, a single cell containing nuclei from both species. During subsequent cell divisions, the chromosomes from one species (usually the human chromosomes) are randomly lost, while the other species’ chromosomes remain stable. This allows researchers to correlate the presence of specific human chromosomes with the expression of specific genes.

Procedure

1. Cell Fusion:

   1. Cells from two species are fused using agents like polyethylene glycol (PEG) or by electrical stimulation.
   2. A hybrid cell (heterokaryon) is formed, containing both sets of parental chromosomes.

2. Chromosome Loss:

   1. Human chromosomes are preferentially lost over successive generations.
   2. Each hybrid cell retains a unique subset of human chromosomes.

3. Gene Expression Analysis:

   1. Hybrid cells are analyzed for the presence of a specific gene product (e.g., enzyme, protein).
   2. The expression of the gene is correlated with the retained human chromosomes.

4. Chromosome Identification:

Techniques like karyotyping or molecular markers are used to identify the retained chromosomes in hybrid cells.

Applications of Somatic Cell Hybridization in Gene Mapping

1. Assigning Genes to Chromosomes:

   • By analyzing which human chromosome is present in hybrid cells expressing a particular gene, the gene’s location can be determined.

2. Gene Localization:

   • Narrowing down gene positions to specific chromosomal regions.

3. Studying Chromosome Function:

   • Understanding the role of specific chromosomes in gene expression and cell behavior.

4. Development of Genomic Resources:

   • Aiding in the construction of physical maps and genome sequencing.

Advantages

• Allows mapping of genes in species where traditional breeding is not possible.
• Can be used to map genes in humans.
• Provides a rapid and efficient method for gene localization.

Limitations

• Random loss of chromosomes may lead to incomplete data.
• Limited resolution; fine mapping may require additional methods.
• Expression of some genes may be influenced by the hybrid cell environment.

Conclusion

Gene mapping by somatic cell hybridization is a valuable technique in genetics, especially for human studies. It has greatly contributed to our understanding of gene-chromosome associations and remains a cornerstone in the field of molecular and cellular biology.