H Histidine in proteins hairpin A region of single stranded DNA or RNA that folds back on
itself to form a double helix haploid A cell or organism having only one copy of each
chromosome. haploid set The chromosomes in a haploid cell or individual haplotype The specific allelic constitution of a chromosome. Often,
the allelic composition o fone or a few linked genes under
investigation. haploinsufficiency The situation where inactivation of a gene on one pair of
homologous chromosomes results in a change in the phenotype
of the mutant organism Hardy-Weinberg equilibrium A condition under which the genotypic frequencies in a
diploid population are euqal to the products of the allele
frequencies involved. hash table A listing of the positions at which all words of a fixed
length (word size or ktup) occurs in a query sequence. The
FASTA database searching program uses a hash table
approach. helical wheel A graphical view of the asymmetry of the distribution of
hydrophobic side chains in potential alpha-helices helicase An enzyme that breaks base pairs in a double-stranded DNA
molecule helix-turn-helix motif a common structural motif for attachment of a protein to
a DNA molecule. hemoglobin The primary functional protein of red blood cells. It is
involved with binding and transporting oxygen. heterchromatin Chromatin that is relatively condensed and is thought to
contain DNA that is not being transcribed heteroduplex A double-stranded nucleic acid molecule in which each
strand has been derived from a different individual heteroduplex analysis Transcript mapping by analysis of DNA-RNA hybrids with a
single-stranded-specific nuclease such as S1 heterogeneous nuclear RNA hnRNA. RNA transcripts in the nucleus, representing
precursors and processing intermediates of rRNA, mRNA, and
tRNA, as well as mature RNA transcripts not yet transported
into the cytoplasm. heteropolymer An artificial RNA comprising a mixture of different
nucleotides heterozygosity A measure of genetic variation in a population calculated
either as the mean frequency of heterozygotes over all loci
(observed heterozygosity), or as the mean frequency of
heterozygotes expected in a population in Hardy-Weinberg
equilibrium (expected heterozygosity or gene diversity). heterozygote A diploid individual with different alleles at the locus
in question Heuristic algorithm An economical strategy for deriving a solution to a
problem for which an exact solution is computationally
impractical or intrractable. Consequently, a heuristic
approach is not guaranteed to find the optimal ro "true"
solution. heuristics A term in computer science that refers to 'guesses" made
by a program to obtain approximately accurate results.
Typically, these are used to increase the speed of a program
greatly at the cost of potentially yielding suboptimal
results. BLAST and FASTA use heuristics based on knowledge
of how sequeences evolve. Hidden Markov Models HMM. The extension of a Markov model. A pattern
recognition method that can be used to represent the
alignment o fmultiple sequences or sequence segments by
attempting to capture common patterns of residue
conversion. High-throughput DNA sequencing Experimental procedures for determining massive amounts
of genomic DNA or cDNA sequence data using highly automated
sequencing machines. higher taxon A taxon above the species level highly repetitive DNA The fraction of genomic DNA consisting of sequences
repeated on the average hundreds of thousands of times. highly repetitive genes Functional genes appearing in numerous copies in the
haploid genome. histone One of the basic proteins found in nucleosomes. Helps the
DNA wind tightly in the chromosomes. Holliday structure An intermediate structure formed during recombination
between two DNA molecules Homeodomain or Homeobox A DNA-binding motif found in many proteins involved in
developmental regulation of gene expression. A DNA sequence
to which regulatory proteins bind, affective major features
of the organism's development. These sequences are highly
conserved across many species. homeotic mutation A mutation that results in the transformation of one body
part to another. In Drosophila, the Antennapedia
(Antp) mutation changes an antenna into a leg.. homeotic selector gene A gene that establishes the identity of a body part such
as a segment of the Drosophila embryo. homoduplex A double-stranded DNA, the complementary strands of which
are derived from the same individual. homologous In phylogenetics, describing particular features in
different individuals that are genetically descended from
the same feature in a common ancestor. In molecula rbiology,
often "homologous" simply means similar, regardlessof
genetic relationship. homologous chromosomes Two or more identical chromosomes present in a single
nucleus. homologous protein Two proteins that are related by common evolutionary
history. homology Similarity by common ancestry or genetic relatedness. homology domain A region in a protein sequence with similarity to an
otherwise unrelated protein. This term should be used only
if the region is of a size sufficient to form a domain, A
homology domain can contain several motifs. homology searching A technique in which genes with sequences similar to that
of an unknown gene are sought, the objective being to gain
an insight into the function of the unknown gene. homoplasy Similarity that has evolved independently and is not
indicatavie of common phylogenetic origin homozygote A diploid individual with identical alleles at one or
more loci. horizontal evolution concerted evolution horizontal gene transfer The transfer of tenetic information from one genome to
another, specifically between different species host Any computer on the Internet that can be addressed
directly through a unique IP address hotspot of mutation A segment of genomic DNA that shows a high propensity to
mutate either spontaneously or under the action of a
particular mutagen. HPLC High Performance Liquid Chromatography. A column
chromatography method with many applications in
biochemistry. Hsp70 chaperone A family of proteins that bind to hydrophobic regions in
other proteins in order to aid their folding High throughput genome sequences. Various genome
sequencing centers worldwide have begun the large-scale
sequencing o fhuman and other higher eukaryotic genomes the
databases put the unfinished sequences thar are the result
of such sequencing efforts in a separate division. These
unfinished recores, in most cases, are notable for important
numbers of gaps in the nucleotides, low accuracy, and no
annotations on the record. HTML Hyper Text Markup Language. The standard, text-based
language used to specify the format of World Wide Web
documents. HTML files are translated and rendered through
the use of Web browsers. Human Genome Initiative Collective name for several projects begun in 1986 by
Department of Energy to (1) create an ordered set of DNA
segments from known chromosomal locations, (2) develop new
computational methods for analyzing genetic map and DNA
sequence data, and (3) develop new techniques and
instruments for detecting and analyzing DNA.This DOE
initiative is now known as the Human Genome Program. The
national effort, led by DOE and NIH, is known as the Human
Genome Project. Human Genome Project (HGP) An international research effort begun in the 1980s to
map and sequence the human genome, and other model genomes,
and to disseminate the map and sequence information. HGP
also has a major component to investigate the Ethical, Legal
and Social Issues (ELSI) of the human genome research. hybrid dysgenesis A syndrome of correlated abnormalities that is
spontaneously induced in one type of hybrid between certain
mutually interactive strains of Drosophila, but not in the
reciprocal hybrid hybridization The attachment by base-pairing of two complementary
polynucleotides. Hybridization of a single stranded probe to
a longer sequence of DNA is often used to determine where
the complement of the probe resides in the longer
sequence. hybrid vigor overdominance hydrogen bond A weak, noncovalent bond between a hydrogen atom, and an
electronegative atom such as oxygen or nitrogen. Hydrogen
bonds are the forces that hold together DNA, RNA and
proteins in their 3D structure. hydropathic Hating water. An amino acid residue with an aliphatic or
aromatic side chain (phenylalanine) . hydrophilic Liking water. An amino acid residue with a polar side
chain (lysine, aspartic
acid) hydrophobic Fearing water. An amino acid residue with an aliphatic or
aromatic side chain hydrophobic effects Chemical interactions that result in hydrophobic groups
becoming buried inside a protein. hydrophobic mooment A quantitative measure of the asymmetry of the
distribution of hydorphobic-side chains in alpha-helices and
beta-strands. hypervariable site/region A DNA or protein region that exhibits excessive
intraspecific variability. Maintenance of so much
variability usually requries the locus to be subject to a
form of balancing selection, such as overdominance. hyperlink A graphic or text within a World Wide Web document that
can be selected by means of a mouse. Clicking on a hyperlink
transports the user to another part of the same Web page or
to another Web page, regardless of location. hypermutation A increase in the mutation rate of a genome
