What is genomic selection?

In genomic selection (GS) the genetic potential of an animal (in other words the breeding values, BV) is estimated by taking into account the thousands of markers which are spread across the entire genetic material. In this context a marker is an SNP (Single Nucleotide Polymorphism, pronounced Snip.) SNPs can be determined relatively cost-effectively in the laboratory and even for a young animal – and now even in an embryo.
Once the relationships between the SNPs and the traits that interest us have been determined, breeding values can be calculated with the SNP information from the laboratory (“direct genomic breeding value” or DGV). To improve reliability of these “laboratory breeding values” traditional information sources are then added (breeding value of the parents) – and if available – details on performance and information on progeny and expressed in a combined breeding value as genomic optimized breeding value (GOBV). Genomic breeding values are – with the correct estimate and especially in young animals – more reliable than traditional breeding values (see breeding value reliability). This opens up new breeding related possibilities.

Genetic bases

Genetic material (genome) of living beings is located in the cell nuclei, broken down into individual chromosomes. Bovine cells – apart from the gametes - each contain a total of 2 x 30 chromosomes, half of which originate from the father and half from the mother. The chromosomes contain DNA, a long thread-like molecule that consists of individual bases (four individual bases: A, C, G and T). In the DNA double-strand bases A and C always form a pair as do G and T (base pair, see graphic). The sequence of the bases in the DNA double strand (for example, TCGGATA etc.) form the genetic code.

The entire bovine genome contains around 3 billion base pairs. One section on the DNA strand, which contains the instructions (code) for forming a protein, is called a gene. One gene consists on average of about 4,000 base pairs. In total there are an estimated 30,000 genes in the bovine genome. Genes only comprise about 5% of the total genome. The function of the remaining 95% of the base pairs in the genome is in parts still unknown.

A variation in the genome on one individual base pair (example AAGGTTA and ATGGTTA) is called a Single Nucleotide Polymorphism (SNP, pronounced Snip). SNPs occur very frequently in the genome (in more than 1 million locations), but generally have no effect on a trait. SNPs can be determined relatively easily in the laboratory (see “How are SNPs determined in the laboratory?” and are therefore interesting markers.