Haploid cell
A cell containing only one set, or half the usual (diploid) number, of chromosomes

Haplotype
1. A group of alleles, each from a different locus in the same region of a chromosome, that exist in the same double helix.

Haplozygous
See hemizygous

Hardy-Weinberg equilibrium
The frequencies of genotypes at a locus resulting from random mating t that locus; for two alleles, Al and A2, with respective frequencies p and q, the Hardy Weinberg equilibrium frequencies are p2 AlA1, 2pq A1A2, q2 A2A2. Despite the simplifying assumptions required to predict these frequencies, most loci in most populations are in Hardy-Weinberg equilibrium. Thus the Hardy Weinberg law, which predicts these frequencies, is one of the great unifying themes of biology. harvesting 1. The process involved in gathering in ripened crops. 2. The collection of cells from cell cultures or of organs from donors for the purpose of transplantation.

Helper plasmid.
A plasmid that provides a function or functions to another plasmid in the same cell.

Helper T cells
See helper cells.

Helper T lymphocytes
See helper cells.

Helper cells
T cells that respond to an antigen displayed by a macrophage by  stimulating B and T lymphocytes to develop into antibody producing plasma cell  and killer T cell respectively.

Helper virus
A virus that provides a function or functions to another virus in the same cell.

Hemicellulase
An enzyme that degrades hemicellulose to galactose; hemicellulase is available as a commercial product.

Hemicellulase
(Gr. hemi, half + cellulose) Any cellulose-like carbohydrate but with differing chemical composition. Together with pectin  and lignin, hemicelluloses form the cell wall matrix.