Advances in Understanding Chromosomal Abnormalities in Livestock

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Introduction

Chromosome aberrations in livestock have over the decades generated substantial attention and interest to be detected as owing enormous influence on animal breeding, fertility levels, and overall productivity of farms. All these abnormalities, from translocations and duplications to aneuploidies or chimerisms, can be very deleterious for the genetic health and reproduction capacity of livestock, predicting significant difficulty in attaining a suitable number of pregnancies. In recent years, due to improvements in cytogenetic and molecular techniques, great achievement has been made in identification as well as understanding these chromosomal aberrations. In this review, we discuss recent advances and methods to study chromosomal abnormalities in livestock species and their consequences on animal breeding and genetic management.

Chromosome Abnormalities in Seven Livestock Species

In other words, alterations can again be classified into numerical and structural categories. Numerical abnormality shifts include variation in the number of chromosomes and need-based aneuploidies with surplus or deficiency chromosomes. They include translocations, inversions, duplications, etc., but special emphasis should be placed on Robertsonian translocations and reciprocal translocations in terms of frequency and fertility.

Robertsonian Translocations

Robertsian translocations, as we know, are one of the types of chromosomal rearrangements that are evident in cattle. This is because two acrocentric chromosomes get to their centromere and form a single metacentric chromosome. Of course, that means one less chromosome and has an unbelievable impact on the ability to reproduce. For example, the clinically most apparent one in bovine, which leads to reduced fertility, is the Robertsonian translocation 1;29. This translocation has been fully investigated and documented regarding the many breeds of cattle from all over the world. Technological improvement has since created the possibilities of correct identification and characterization of such Robertsonian translocations. Techniques that can be used now to detect these kinds of chromosomal abnormalities include FISH and array CGH. The latter enables the confirmation of the translocation and identification of the breakpoint and the involved chromosome.

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Reciprocal Translocations

An example of chromosome abnormalities is when two non-similar chromosomes swap material, which is known as reciprocal translocations. These translocations can result in balanced or unbalanced gametes during meiosis, with reproductive rates being substantially affected. In livestock, reciprocal translocations have been described as a chief explanation of sterility and embryonic mortality.

Another relevant report described the case of a Friesian bull that was heterozygous for a 3/16 Robertsonian translocation; in the six analyzed spermatocytes, only one cell produced unbalanced gametes, so it was concluded that 3/16 Robertsonian translocations might not always affect fertility. Nonetheless, ICE was detected, which means that these translocations can affect the segregation of other chromosomes; thus, breeding results are weighted with fluctuations.

Aneuploidies and Chimerism

Numerical abnormalities, including aneuploidies, when an organism contains an incorrect number of chromosomes, are not so frequent, but they cause significant harm to the leading livestock. For example, studies have shown that in cattle with an X-monosomy (59, X0), individuals resulting from such a mechanism would be sterile or at best subfertile; besides, other phenotypic expressions occur. Likewise, the conditions with two or more genetically different cell lines in an individual known as chimerism cause DSD and infertility.

In sheep, an example of the presence of XX/XY blood chimeras was described; the identified animals were listed as females but had features of both male and female animals. This condition is referred to as freemartinism, and it affects women with lesbian sexual preferences. or heterosexuals who have twin pregnancies; it is a leading cause of infertility in female livestock.

Genetic and Cytogenetic Techniques

Current developments in genetic and cytogenetic frameworks have eased the identification and characterization process of chromosomal abnormalities in livestock. Conventional G-banding has been effective like any other karyotyping technique, but it also mostly fails to identify minor chromosomal translocations. Today’s methods, including FISH, array CGH, and SNP arrays, have changed the course greatly to give a high-resolution description of the structures and other abnormalities of chromosomes.

To this end, FISH is a very valuable technique, especially in the analysis of chromosomal translocations, such as in the case of acute myeloid leukemia. For example, certain DNA probes tagged with fluorescent dyes may enable chromosomal rearrangements to be visualized and thus be located; for example, in several studies undertaken, probes were used for the characterization of Robertsonian and reciprocal translocations in cattle, sheep, and buffalo.

Array-CGH, on the other hand, facilitates the examination of the status of copy number variation in the entire genome. Such techniques come in handy in the detection of deletions and duplications of chromosomal disorders. The single nucleotide polymorphism arrays, or SNP arrays, have also had a hand in the detection of aneuploidies as well as other chromosomal aberrations at the single nucleotide level.

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Case Studies and Clinical Implications

Several case reports have underlined the clinical impact of chromosomal anomalies in livestock. For example, various congenital malformations were witnessed in a Holstein calf that had an unusual karyotype mosaic with a marker chromosome. In this case, the cytogenetic study showed how such a marker chromosome was responsible for these developmental anomalies, outlining one more time the need for detailed genetic screening during breeding programs.

In another example, a new Robertsonian translocation between chromosomes 3 and 16 was described in a young Marchigiana bull. This translocation did not appear to seriously affect the reproductive ability of this bull, further proof that chromosomal anomalies do not result in serious fertility problems. However, in this case, interchromosomal effects were detected, underscoring the complexity of chromosomal interactions and their potential implications for breeding outcomes. Chromosomal abnormalities have been supported by much empirical evidence with various clinical consequences in livestock. For example, a naturally born Holstein calf had a karyotype that was a mosaic and which included a marker chromosome with many congenital malformations. Further, the chromosomal analysis showed this particular marker chromosome involved in the developmental pathology of offspring, and this study proposed there is a need for uncompromised genetic analysis in breeding stock.

In another study, authors reported a case of a Marchigiana young bull affected by a new Robertsonian translocation between chromosomes 3 and 16. In this bull described in the case, the above-mentioned translocation didn’t hamper the animal’s potential to reproduce, thus proving that chromosomal aberrations do not always result in serious fertility consequences. The identification of the interchromosomal effects in this particular case, however, helped to broaden the understanding of chromosomal interaction possibilities and their influence on breeding processes.

Recommendations and Genetic Counseling

The developments made in learning about chromosomal aberrations in animals have important consequences for genetic selection and breeding. With the use of genetic and cytogenetic testing in selecting mating pairs, there is always the potential of recognizing chromosomal anomalies among the prospective mates and therefore reducing the of to the examined populations.

So, it is recommended to continue studying the possibilities of creating more effective and less expensive screening techniques and to investigate the genetic causes of chromosomal disorders. The discovery of the reasons for such abnormalities can be useful for enhancing female livestock fertility and, consequently, productivity.

Also, the incorporation of genomic technologies like WGS and CRISPR-based gene editing may help in expanding efficiency in identifying specific chromosomal abnormalities and help in correcting the same. Such technologies could provide a clear direction toward enhancing accuracy and efficiency in the population’s management as well as better health standards within the livestock population.

Conclusion

Research on chromosomal abnormalities in animals has recently received substantial development owing to the available genetic and cytogenetic procedures. Knowledge of such variations is vital in enhancing the genetic qualities of livestock, genetic health, and population stability among the stock. Furthering the study of chromosomal rearrangements and their effects, scientists would be able to come up with better ways of handling these complications, thus improving the general well-being of livestock.

References

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