Gene Mapping | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Gene Mapping Overview

• Each mammal and bird species likely contains between 50,000 to 100,000 genes.
• The goal is to identify, understand functions, and document allelic variations of all genes.
• Genetic mapping is a crucial first step in this process.

Types of Genetic Maps

Linkage Map:

• Consists of linked genes arranged based on recombination fractions.
• Created by estimating recombination fractions between various loci.

Physical Map:

• Indicates gene locations on chromosomes.
• Generated using methods like somatic-cell hybrids to identify specific loci.

Advancements in Genetic Mapping:

• Molecular technologies, like microsatellites, enable extensive DNA polymorphism detection.
• Linkage mapping methods have evolved, including single-sperm typing for direct recombination frequency estimates.
• PCR detection of microsatellites is a popular and effective method in gene mapping.

Creating Linkage Maps:

• Estimating recombination fractions involves crossing genetically diverse populations.
• First-cross (F1) and backcross (BC) generations are used to maximize heterozygosity and estimate recombination fractions.
• Genotyping offspring helps infer gamete frequencies and estimate recombination.

Single-Sperm Typing:

• Utilizes flow-sorting sperm cells for direct estimates of recombination frequency.
• Requires no matings, only a sample of sperm cells from a heterozygous male.

Physical Map Generation:

• Uses somatic-cell hybrids to detect locus presence in different cell lines.
• Concordant DNA markers indicate chromosome locations.
• Allows for finer marker location, identifying syntenic groups and linkage groups.

Physical Mapping Techniques

• Physical mapping involves in situ hybridization of cloned DNA to its corresponding site on the chromosome.
• Initially, radioactive labelling of cloned DNA was used, but now, a more effective non-radioactive method called fluorescence in situ hybridization (FISH) is employed.

Chromosome-Specific DNA Libraries

• Chromosome-specific DNA libraries are prepared, containing DNA from a single chromosome.
• These libraries can be obtained from chromosomes separated by methods like FACS or microdissection.
• Micro-dissection allows the selection of specific portions of a chromosome, enabling the creation of microclone libraries for those specific sections.

Chromosome Painting

• To confirm the specificity of DNA libraries, samples are hybridized to a complete chromosome spread using FISH.
• If the library is correct, the relevant chromosome or part will fluoresce, indicating successful chromosome painting.

Impact and Results

• This technology results in a series of DNA libraries covering each chromosome region.
• These libraries can be divided into overlapping YAC clones, providing a contiguous set of YAC clones covering the entire genome.
• Once a gene is located within a YAC clone, its physical location is pinpointed, facilitating isolation with further resources.

Genetic Mapping Efforts

• Major domestic species are collaborating globally to create genetic maps that integrate information from both linkage and physical maps.

By employing advanced techniques like FISH and microdissection, researchers can precisely map DNA sequences to specific chromosomes, facilitating the identification and isolation of genes within a genome. This collaborative effort across species aims to create comprehensive genetic maps that enhance our understanding of genetic structures and functions.