BREEDING ▶▶▶
Data model to avoid chromosomal defects
During the formation of egg and sperm cells, or the separation of chromosomes immediately after conception, errors might occur than can affect fertility. The Danish Pig Research Centre (DPRC) has developed a model to minimise the risk of such chromosomal defects.
BY BIRGITTE ASK, SENIOR SCIENTIST, DANISH PIG RESEARCH CENTRE I
n all mammals, humans and pigs included, the body consists of trillions of cells. These cells contain the genes that are necessary for body functions. The genes are encoded in the DNA that is coiled into structures called
chromosomes. For instance, pigs have genes that promote their daily weight gain, their ability to survive or their fertility in comparison to other pigs. The essence of the DanBred breeding programme, which is managed by the Danish Pig Research Centre (DPRC), is to continuously mate the pigs with the best genes to im- prove these traits for all future generations. However, chro- mosomal defects may occur when genes are passed on between generations.
Fertility is the goal The risk of inherited chromosomal defects, such as the “trans- locations”, may be reduced substantially. During the forma- tion of germ cells, the chromosomes are segregated to pass on half of the gene pool to the offspring. In the earliest stage
Translocations
In the earliest stage after conception, chromosomes first segregate within the gametes or haploid cells, and then when joined, the chromosomes from the boar and the sow fuse together. Thereby, the offspring inherit half of their moth- er’s and half of their father’s genes. However, in a few cases the segregation or fusion is imperfect. Part of one chromosome, e.g. chromosome 1, may be swapped with part of another chromosome, e.g. chromosome 7. In some cases, such a translo-cation results in some genes no longer being expressed correctly, which may ultimately lead to re-duced fertility.
20 ▶PIG PROGRESS | Volume 36, No. 1, 2020
after conception, the chromosomes of the sow and boar fuse together, and their offspring inherits half of the genes from the dam and half from the sire. Occa-sionally, this fusion of the chromosomes is defective. A reciprocal translocation is a defect where parts of non-matching chromosomes are fused, so that, for example, part of chromosome 7 is fused to chro- mosome 14 and vice versa. This may sometimes result in reduced fertility. In a French study of several pig breeds, inherited transloca- tions were estimated to appear in about 1 in 200 normal functioning young purebred boars (0.5%). However, far from all translocations affect the fertility of pigs. Therefore, AI boars should not necessarily be culled just because a translocation has been detected. Therefore, the DanBred breeding programme focuses on tar- geting translocations and other possible chromosomal de- fects that adversely affect fertility, while simultaneously maximising genetic gain.
Accurate testing is key Accurate testing is key. There are at least two options to test
Schematic illustration as to how translocation occurs at DNA level.
ILLUSTRATION: DANBRED
PHOTO: DANBRED
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