Cytogenetics | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Cytogenetics in Farm Animals

• Cytogenetics is the study of chromosome numbers, morphology, and variations in number and structure in animals.
• Chromosomes are carriers of genes, the hereditary material passed down from parents to offspring.

• Modern cytogenetics began in 1952 with the method of swelling cells for chromosomal separation and counting.
• In 1960, techniques for chromosomal preparation and inducing cell division were described.

• Human cytogenetics advanced earlier than animal cytogenetics, with the discovery of chromosomal abnormalities like Turner's, Klinefelter's, and Down's syndromes.
• Animals have two sets of chromosomes in somatic cells, with one set from each parent.

• Chromosomes are classified as metacentric, submetacentric, telocentric, and acrocentric based on the position of the centromere.
• Chromosomes have p and q arms, with the international nomenclature standardizing their naming conventions.

• Animal chromosomes are named following a standardized procedure, such as 60, XY for a bull.
• Deletions, trisomies, chimerism, and structural changes are denoted using specific symbols.

• A cow with trisomy of the 18th chromosome pair: 60, XX, 18.
• Sex chromosome chimerism in a Freemartin: 60, XX/30, XY.
• Robertsonian translocation in a bull involving the 1st and 29th chromosomes: 59, XY, t(1q;29q).

Chromosomal Complements and Abnormalities in Farm Animals

• Diploid Autosomal No. 2n
• Sex Chromosomes: X

Animal Chromosomal Complements:

• Cattle (Bos taurus): 60
• Cattle (Bos indicus): 60
• Buffalo (River type): 50
• Buffalo (Swamp type): 60
• Horse: 64
• Sheep: 54
• Goat: 60
• Dog: 78
• Pig: 38
• Cat: 38

• Sex chromatin presence in female nerve cells
• Sex chromatin absence in male cells
• Sexual dimorphisms in polymorphonuclear leucocyte

• Causes of infertility in farm animals
• Effects of genetically balanced autosomal abnormalities
• Specific cases in horses, cattle, sheep, goat, and pig
• Impact of chromosomal abnormalities on fertility

• Testicular hypoplasia and its association with chromosomal aberrations
• Chromosomal aberrations in bulls with testicular hypoplasia

Chromosomal Aberrations in Farm Animals

• Chromosomal gaps have been observed in bulls exhibiting testicular hypoplasia, impacting their reproductive health.

• In animals, sex chromosomal aberrations can lead to intersexuality, affecting gonad differentiation and subsequent reproductive system development.
• Abnormal sex chromosomes can influence the development of the Wolffian and Mullerian duct system, urogenital sinus, and external genitalia.

• In cattle, the occurrence of female twins of male calves is relatively common and can result in anatomical conditions like true hermaphroditism or male pseudohermaphroditism.
• Female twins of male calves may have a chromosomal complement of 2n, XX/2n, XY in their blood cells.

• In farm animals, chromosomal abnormalities can lead to various congenital conditions such as brachygnathia, hydrocephalus, cardiac defects, and more.

• Interspecies hybridization in farm animals can result in reduced fertility, with complete sterility more common in males than in females.
• Hybrids with minor differences in parental chromosome sets may exhibit reduced fertility, while those with major differences may experience gametogenesis failure and sterility.

• Horse Hybrids: Mules and hinnies, offspring of horse and donkey hybrids, are sterile due to differences in their chromosomal complements.
• Cattle Hybrids: Hybrids between different cattle species like Bos taurus and Bos indicus can be fertile or sterile based on their chromosomal compatibility.
• Sheep and Goat Crossbreeding: Attempts to crossbreed sheep and goats have shown challenges in sustaining pregnancy past six weeks.