Pandora’s Box: Equine Genomics
The genetics of horses has been of great interest to humans for millennia. While we might not have used that term specifically, the recording of equine parentage, births, and deaths was a practice that pre-dated the compulsory recording of human births and deaths in Great Britain by over a century. The term “genomics” covers all aspects of genes, including their structure and function, not just the science of heredity.
The genome is all of the DNA, divided up and packaged as chromosomes, in each cell. The DNA molecule, the unit of heredity, is made up of four nucleotide bases—guanine (G), cytosine (C), adenine (A), and thymine (T)—in a sequence. The equine genome consists of about 2,700 million base pairs, which is similar in size to the human genome.
Less than 3% of the genome actually codes for proteins. The remaining 97% was formerly termed “junk DNA” but we now know it orchestrates the use of the entire genome, as regulatory elements. Individuals have differences in the sequences of the nucleotides. This is pretty obvious—we have greys and bays but they are still horses. However, not all of the sequence differences are that obvious, and sequence differences can be whole sections of sequence or just single nucleotides. A single nucleotide polymorphism (SNP, usually pronounced “snip”) is a single nucleotide in a sequence that differs between individuals at a low-population frequency.
Approximately 10 million SNPs have been found in the collective equine genome. It is important to remember that SNPs are not necessarily mutations that have any effect on the organism. Indeed, SNPs are less likely to be found in the protein coding genes of the genome as these areas have been heavily selected for functionality by evolution. Any change in DNA sequence that did not benefit the animal would reduce its chances of survival in the gene pool
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