Question

How does double-muscling and callipyge mutation phenotypes occur and what are the advantages and disadvantage to the double-muscling and callipyge mutation phenotypes of livestock?

Answer 1

Double muscling

• Certain breeds of cattle, mainly beef, have a high frequency of muscular hypertrophy. This phenomena is called as double muscling.
• This condition is of genetic origin and results from mutations of the myostatin gene.
• Double-muscled animals are characterised by an increase in muscle mass of about 20%. This is because of general skeletal-muscle hyperplasia-that is, an increase in the number of muscle fibers rather than in their individual diameter.

Advantage :-

The main advantage is greatly increased yield of lean meat.

Disadvantages :-

• They have a longer gestation period.
• Low levels of thyroxin as compared to normal cattle.
• Susceptibility to heat stress.
• Small feet and cannon bones which is harmful for animal locomotion.
• Slow growth.
• Underdevelopment of male and female reproductive tract.
• Macroglossia (enlarged tongue) which makes it difficult for the calf to nurse.
• Weak bones, often leading to bone damage of the hooks.
• Erythrocyte fragility.
• Reduced collagen content, measured by reduced hydroxyproline content. This is a good feature of the meat, but makes the bones brittle.
• Changes in pelvic dimensions associated with difficult calving (dystocia).
• Poor lactation.
• They have reduced adipose reserves when subjected to nutritional stress.
• Reduced weight of hide and liver

Callipyge mutation

The callipyge mutation occurs in a gene, now called CLPG1. It seems to have an effect on the activity of nearby genes. Specifically, the mutation may cause genes involved in tissue development to be activated, or expressed, more (or less) than normal.The callipyge mutation is an example of genomic 'imprinting': Imprinted genes are regulated differently in the body depending on which parent they are inherited from. The inheritance of the CLPG phenotype has a non-Mendelian pattern termed polar over-dominance

Advantages :-

They have advantage in retail yield and carcass conformation when compared to normal-muscled cattle.

Disadvantages :-

The disadvantage of the CLPG phenotype is the increased toughness of the Longissimus muscle.