Haploid: Containing only 1 of each pair of the 46 chromosomes (seen in eggs and sperm).

Hardy-Weinberg Law: The mathematical expression of the equilibrium of allelic genetic markers within the population. A mathematical model that allows for the prediction of occurrence of genetic markers in a population and states that in a large random intra-breeding population, not subjective to excessive selection or mutation, the gene and genotype frequency will remain constant over time.

(p + q)2 = P2 + 2 pq + q2 = 1 p and q represent the frequency of two allelic genes in a two allele system. p2 and q2 represent the frequencies of homozygotes. 2pq represents the frequency of heterozygotes. In a multiple allelic system: (p + q + r + s)2 = 1 r and s represent additional alleles in a multiple allele system.

Heredity: The phenomena whereby biological traits are passed from one generation to the next. Heredity results from parents passing genes to their offspring and is why related family members tend to have similar physical characteristics.

Heterozygosity: In forensic science often used to describe the percentage of individ-uals in a population database who are heterozygotes.

Heterozygote (heterozygous): Individual who has two different forms (alleles) of a specific gene. Example: people with the AB blood type have two alleles (A and B) for the blood type gene.

HLA: Human leukocyte antigen, a substance found on the surface of most cells that differs from person to person. One of these, the DQA1 gene, is examined by the most widely used PCR based forensic DNA test.

Homologous: In chromosomes, a pair of chromosomes that contain the same gene (although perhaps different alleles). There are 23 pairs of homologous chromosomes in humans; one of each was contributed by each parent.

Homozygote (homozygous): Individual who has identical forms (alleles) of a given gene. Example: people with the O blood type have two O alleles of the blood type gene.

Hybridization: The joining together of complementary strands of DNA by the process of base pairing when the two strands are from different sources. For example, a DNA strand immobilized on a blot and its complementary radioactively labeled DNA probe.

Hypervariable: A DNA locus that shows extremely high variation in people. Many alleles exist in the population.