Introduction to Quantitative Genetics

Genetic Components of Genetic Variance

Additive genetic variation - variation due to alleles that contribute a fixed value to the metric value of quantitative value; genes that act in this manner contribute to the additive genetic variance (V_A).

Simple Example: yield in a crop; each allele contributes to yield in the following manner

• A allele = 4 bu/ac
• a allele = 2 bu/ac
• B allele = 6 bu/ac
• b allele = 3 bu/ac

Yield Values

AABB genotype yield = 20 (4+4+6+6) bu/ac

AaBb genotype yield = 15 (4+2+6+3) bu/ac.

Dominant Genetic Variation - variation due to alleles that act in a dominant manner; the homozygous dominant and heterozygous genotypes have equal phenotypic values; this source of variability is attributed to the dominance genetic variance (V_D)

Yield Values

AABB genotype yield = 20 (4+4+6+6) bu/ac

AaBb genotype yield = 20 (4+6+6+6) bu/ac.