Gene Numbers and their Estimation in Farm Animals | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Gene Numbers and Estimation in Farm Animals

Estimation of Total Gene Numbers

• The total number of genes in organisms, including Drosophila melanogaster, has not been accurately estimated.
• While 500 different loci have been identified on the chromosome maps of Drosophila melanogaster, many more genes are believed to exist.
• About 289 loci are known to be present on the third chromosome alone.
• The frequency of a gene is defined as the proportion of loci of a given allelic series occupied by that particular gene.

Gene Frequency in Farm Animals

• Gene frequency in farm animals, which have longer generation intervals, is conventionally denoted by the letter q.
• The number of genes reported for most farm animal species is limited and not definitively established.
• There is uncertainty in identifying all genes in observed farm animal populations due to limited sampling.

Gene Numbers for Specific Traits

• Studies have identified a few pairs of genes responsible for breed differences in milk yield and fat percentage in farm animals.
• Experiments with different cattle breeds suggest that multiple gene pairs influence various traits such as fat percentage.
• Characteristics controlled by gene numbers in farm animals typically range from 5 to 20 or more.

Estimating Total Gene Numbers

• Quantitative genetic experiments indicate that the number of genes involved in a trait cannot be less than a certain threshold.
• Continued genetic investigations often reveal more genes associated with specific traits over time.
• Sampling errors and other factors can lead to overestimation or underestimation of gene numbers in farm animals.