ich contain genes that influence development and form of the new organism. Chromosomes are composed of deoyxribonucleic acid (DNA) and are located in the nucleus of the cell. In the sex cells (testes and ovaries in humans), meiosis creates gametes with haploid chromosome sets: each gamete contains half of the chromosomal information necessary to create a new organism. The moment of conception occurs when the male and female gametes unite, forming a zygote which has a complete, diploid chromosome set. While the male contributes only his gamete, the female in addition to her gamete contributes cytoplasm which nourishes the developing zygote as well as specific proteins that direct cell differentiation. Along with mutation, meiosis assists in maintaining diversity of a population: the homologues of each chromosome pair are split so that each gamete receives one from each pair, assuring independent assortment; the homologues also exchange genetic material during recombination. The genotype of an organism, uniquely formed at conception, contains its complete genetic endowment; its phenotype is dependent on its interaction with the environment and consists of its appearance, structure, physiology and behavior. While the phenotype is dependent on the genotype, it may not be assumed that the genotype determines the phenotype a genotype may result in different phenotypes depending on the environment.Quantitative genetics was developed to study traits such as behaviors that are continuously distributed in a population (Stoltenberg & Hirsch, in press). To assess the resemblance between relatives in terms of specific traits, the overall phenotypic variance is partitioned into genetic and environmental components. Genotypic variance is then partitioned into additive, dominance, and interactive variance components. Additive genetic variance, "breeding value," is not strictly additive in the mathematical sense, as it is entirely dependent on the popu...
