Animal Breeding Principles

True/False Questions

• P = BV + GCV + E, where P (phenotype) is influenced by breeding value (BV), gene combination value (GCV), and environmental effects (E).
• Effective crossbreeding does not necessarily require purebred animals.
• Breeding Value (BV) represents the part of the genetic makeup (G) that is passed from parent to offspring.
• Breeding Value is indeed the sum of independent, additive gene effects that are transmittable to offspring.
• Only one of each gene pair can be transmitted from parent to offspring because genes can't be transmitted in pairs.
• Hybrid vigor (heterosis) results from non-additive genetic merit (dominance and epistasis effects).
• Environmental effects can be temporary or permanent.
• Random drift alters gene frequencies from generation to generation due to chance.
• Independent gene effects are additive, and Breeding Value for a trait is the sum of these effects across all loci.
• Seedstock breeders sell animals and information.

Multiple Choice Questions

• Four factors to consider before including a trait in a selection program: heritability, genetic correlation, ease of measurement, and economic importance.

• Migration is the movement of individual animals into, or out of, a population.

• Discovering and identifying genetic defects often results from breeding to a common ancestor.

• A permanent environmental effect would impact traits like milk production in dairy cattle or any repeated trait.

• The six-locus genotype expected to breed with the most prepotence is the one that is the most homozygous across loci.

• If a bull has a breeding value (BV) of 250 for Yearling Weight, the progeny difference (PD) = 1/2 BV = 125.

• The statement "In the absence of selection, mutation, migration and random drift, the gene and genotypic frequencies of a herd of random mating livestock should never change" describes Hardy-Weinberg Equilibrium.

• DNA tests for recessive alleles do not influence the effectiveness of selection.

• If a population has an average level of milk production of 20,000 lbs, with one cow having a G value of +750 and an E value of -150, the expected level of production is 20,000 + 750 - 150 = 20,600 lbs.

• If Holstein bull mated to many cows produces offspring of 225lbs, progeny difference for milk of the sire is 112.5lbs.

• Animal breeders should select replacements with the best Estimated Breeding Value (EBV).

• Polygenic, quantitative traits follow a normal distribution like threshold traits.

• To determine genotypes, use a DNA test.

Short Answer

• If N is a lethal recessive gene and Nn genotypes have an advantage in fitness over NN, then gene frequency would increase in the population.
• Genotypes AA & Aa would result in highest level of marbling as A is completely dominant to a.
• A new stud ram must be homozygous dominant (NN).