2.9 Key issues in basics of animal breeding (2024)

Owned by Tessa Jacobs
Last updated: aug. 02, 2024 by Kor Oldenbroek
2 min read

  1. A breeding program is characterized by a series of subsequent activities: defining the breeding goal, registration of phenotypes, genotypes and pedigrees, estimation of breeding values for selection traits with a genetic model, selection of parents for the next generation based on estimated breeding values, mating of parents and dissemination of genetic superiority towards the production animals and evaluation of the program with respect to the genetic diversity maintained and realized selection response.

  2. Body cells of mammals and birds have a nucleus where pairs of chromosomes are found. The different number of chromosomes among species impedes the production of crosses between species. Chromosomes are strings of DNA, Deoxyribo Nucleic Acid, which is a macromolecule in the form of a double-stranded helix that carries the genetic information in all cells of higher organisms.

  3. A gene is the hereditary unit, a region of DNA on a chromosome containing genetic information that is transcribed into RNA. This RNA is translated into a polypeptide chain with a physiological function. A gene can mutate to various forms, called alleles.

  4. In all body cells the chromosomes are present in duplo: one originate from the sire and one from the dam. Therefore all genes are present in duplo. These genes might be identical: the allele originating from the sire is identical to the one from the dam. Then an animal is homozygous for that gene. The alleles originating from sire and dam might be different. Then an animal is heterozygous for that gene.

  5. Alleles can be dominant or recessive (interaction between two alleles at a locus), effects can be additive: co-dominance (the value of the heterozygous lies exactly between the two homozygous genotype) or can be over-dominant (the heterozygote has a genotypic value more extreme than either parent).

  6. Alleles of a gene can also interact with alleles of another gene: epistasis.

  7. In sperm cells and oocytes the chromosomes are no longer present in twofold grouped in pairs. In the testis and in the ovary the pairs of chromosomes split in singular chromosomes and each chromosome of a pair goes by chance to a sperm cell or an oocyte. This process is called the meiosis and leads to Mendelian sampling: each sperm cell or oocytes contains a unique combination of alleles from its parent. It is an important event creating genetic diversity.

  8. Due to the events in the meiosis a sperm cell and an oocyte contains 50 % of the DNA of the parent. After the fertilization of an oocyte with a sperm cell the nucleus of the zygote contains again chromosomes in twofold grouped in pairs. This implies that each animal receives half of its chromosomes, half of it genetic value from its sire and half of its dam. Thus the genetic relationship between an animal and each of its parents is 0.5. This is called the additive genetic relationship.