Polygenic Systems and Inheritance of Quantitative Traits | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Polygenic Systems and Inheritance of Quantitative Traits

Most traits important in farm animals are quantitative and have specific characteristics:

• They are influenced by numerous genes, each with minor individual effects. Identifying individual gene impacts on quantitative traits is typically unfeasible.
• Various gene actions like additive, dominance, and epistatic effects play a role, with their significance varying across traits.
• Genetic expression is significantly influenced by the environment, leading to traits with a continuous distribution lacking distinct boundaries between 'good' and 'bad'.

Economic Traits in Livestock

• Economic traits in livestock refer to characteristics that hold a monetary value in livestock production.

Qualitative Traits:

• Qualitative traits exhibit distinct differences between phenotypes, such as the clear contrast between black and red colors in Angus cattle.
• These traits are determined by a pair of genes.

Quantitative Traits:

• Quantitative traits show a continuous range of phenotypes without sharp distinctions and are influenced by multiple gene pairs.
• Examples of quantitative traits include gestation length, birth weight, weaning weight, feed efficiency, carcass quality, milk production, and egg production.
• Environmental conditions significantly impact most quantitative traits, unlike qualitative traits.

Quantitative Inheritance in Farm Animals

• Quantitative inheritance involves complex genetic interactions and environmental influences in traits like backfat thickness in swine.

Genetic Interactions:

• Multiple gene pairs, both additive and non-additive in nature, can contribute to quantitative traits.
• Each gene may not have an equal effect on the trait's expression.

Environmental Influence:

• Environment plays a crucial role in the expression of quantitative traits, alongside genetic factors.

Genetic Variation:

• Offspring exhibit a range of backfat thickness due to genetic diversity, with variations from the parental mean.
• Environmental factors, sex, diet, and other variables contribute to trait expression and variation.

Gene Action and Environment:

• Evidence suggests that gene interactions beyond simple additive effects play a significant role in quantitative trait inheritance.
• Understanding the balance between genetic interactions and environmental influences is key to improving livestock traits through selective breeding.