The human genome is a complete set of nucleic acid sequences for humans, encoded as the DNA within each of the 24 distinct chromosomes in the cell nucleus. A small DNA molecule is found within individual mitochondria. These are usually treated separately as the nuclear genome and the mitochondrial genome. Human genomes include both protein-coding DNA sequences and various types of DNA that does not encode proteins. The latter is a diverse category that includes DNA coding for non-translated RNA, such as that for ribosomal RNA, transfer RNA, ribozymes, small nuclear RNAs, and several types of regulatory RNAs. It also includes promoters and their associated gene-regulatory elements, DNA playing structural and replicatory roles, such as scaffolding regions, telomeres, centromeres, and origins of replication, plus large numbers of transposable elements, inserted viral DNA, non-functional pseudogenes and simple, highly repetitive sequences. Introns make up a large percentage of non-coding DNA. Some of this non-coding DNA is non-functional junk DNA, such as pseudogenes, but there is no firm consensus on the total amount of junk DNA.
The Appaloosa is an American horse breed best known for its colorful spotted coat pattern. There is a wide range of body types within the breed, stemming from the influence of multiple breeds of horses throughout its history. Each horse's color pattern is genetically the result of various spotting patterns overlaid on top of one of several recognized base coat colors. The color pattern of the Appaloosa is of interest to those who study equine coat color genetics, as it and several other physical characteristics are linked to the leopard complex mutation (LP). Appaloosas are prone to develop equine recurrent uveitis and congenital stationary night blindness; the latter has been linked to the leopard complex.
Molecular genetics is a branch of biology that addresses how differences in the structures or expression of DNA molecules manifests as variation among organisms. Molecular genetics often applies an "investigative approach" to determine the structure and/or function of genes in an organism's genome using genetic screens.
In genetics and bioinformatics, a single-nucleotide polymorphism is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently large fraction of the population, many publications do not apply such a frequency threshold.
The International HapMap Project was an organization that aimed to develop a haplotype map (HapMap) of the human genome, to describe the common patterns of human genetic variation. HapMap is used to find genetic variants affecting health, disease and responses to drugs and environmental factors. The information produced by the project is made freely available for research.
Comparative genomics is a branch of biological research that examines genome sequences across a spectrum of species, spanning from humans and mice to a diverse array of organisms from bacteria to chimpanzees. This large-scale holistic approach compares two or more genomes to discover the similarities and differences between the genomes and to study the biology of the individual genomes. Comparison of whole genome sequences provides a highly detailed view of how organisms are related to each other at the gene level. By comparing whole genome sequences, researchers gain insights into genetic relationships between organisms and study evolutionary changes. The major principle of comparative genomics is that common features of two organisms will often be encoded within the DNA that is evolutionarily conserved between them. Therefore, Comparative genomics provides a powerful tool for studying evolutionary changes among organisms, helping to identify genes that are conserved or common among species, as well as genes that give unique characteristics of each organism. Moreover, these studies can be performed at different levels of the genomes to obtain multiple perspectives about the organisms.
Nyctalopia, also called night-blindness, is a condition making it difficult or impossible to see in relatively low light. It is a symptom of several eye diseases. Night blindness may exist from birth, or be caused by injury or malnutrition. It can be described as insufficient adaptation to darkness.
Genetics, a discipline of biology, is the science of heredity and variation in living organisms.
A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation that can be observed. A genetic marker may be a short DNA sequence, such as a sequence surrounding a single base-pair change, or a long one, like minisatellites.
Gene mapping or genome mapping describes the methods used to identify the location of a gene on a chromosome and the distances between genes. Gene mapping can also describe the distances between different sites within a gene.
The Human Genome Project (HGP) was an international scientific research project with the goal of determining the base pairs that make up human DNA, and of identifying, mapping and sequencing all of the genes of the human genome from both a physical and a functional standpoint. It started in 1990 and was completed in 2003. It remains the world's largest collaborative biological project. Planning for the project began in 1984 by the US government, and it officially launched in 1990. It was declared complete on 14 April 2003, and included about 92% of the genome. Level "complete genome" was achieved in May 2021, with only 0.3% of the bases covered by potential issues. The final gapless assembly was finished in January 2022.
Varnish roan describes a horse with coloration similar to roan, but with some changes in color over the years, though not to the extreme of a gray. This type of roaning only occurs in conjunction with the Leopard complex. Varnish roans are born with a dark base coat color, usually with some spotting. As the horse ages, white hairs increase over most of the body, and many spotted markings blur or fade. The varnish roan pattern often appears to spread from the white of any original markings. This color pattern is best known in the Appaloosa breed of horse.
A tag SNP is a representative single nucleotide polymorphism (SNP) in a region of the genome with high linkage disequilibrium that represents a group of SNPs called a haplotype. It is possible to identify genetic variation and association to phenotypes without genotyping every SNP in a chromosomal region. This reduces the expense and time of mapping genome areas associated with disease, since it eliminates the need to study every individual SNP. Tag SNPs are useful in whole-genome SNP association studies in which hundreds of thousands of SNPs across the entire genome are genotyped.
Congenital stationary night blindness (CSNB) is a rare non-progressive retinal disorder. People with CSNB often have difficulty adapting to low light situations due to impaired photoreceptor transmission. These patients may also have reduced visual acuity, myopia, nystagmus, fundus abnormalities, and strabismus. CSNB has two forms -- complete, also known as type-1 (CSNB1), and incomplete, also known as type-2 (CSNB2), which are distinguished by the involvement of different retinal pathways. In CSNB1, downstream neurons called bipolar cells are unable to detect neurotransmission from photoreceptor cells. CSNB1 can be caused by mutations in various genes involved in neurotransmitter detection, including NYX. In CSNB2, the photoreceptors themselves have impaired neurotransmission function; this is caused primarily by mutations in the gene CACNA1F, which encodes a voltage-gated calcium channel important for neurotransmitter release. CSNB has been identified in horses and dogs as the result of mutations in TRPM1, GRM6, and LRIT3 .
Hereditary equine regional dermal asthenia (HERDA), also known as hyperelastosis cutis (HC), is an inherited autosomal recessive connective tissue disorder. It develops from a homozygous recessive mutation that weakens collagen fibers that allow the skin of the animal to stay connected to the rest of the animal. Affected horses have extremely fragile skin that tears easily and exhibits impaired healing. In horses with HC, the skin separates between the deep and superficial dermis. There is no cure. Most affected individuals receive an injury they cannot heal, and are euthanized. Managed breeding strategy is currently the only option for reducing the incidence of the disease.
The following outline is provided as an overview of and topical guide to genetics:
The leopard complex is a group of genetically related coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to graying or roan to distinctive, Dalmatian-like leopard spots on a white coat. Secondary characteristics associated with the leopard complex include a white sclera around the eye, striped hooves and mottled skin. The leopard complex gene is also linked to abnormalities in the eyes and vision. These patterns are most closely identified with the Appaloosa and Knabstrupper breeds, though its presence in breeds from Asia to western Europe has indicated that it is due to a very ancient mutation.
Dominant white (W) is a group of genetically related coat color alleles on the KIT gene of the horse, best known for producing an all-white coat, but also able to produce various forms of white spotting, as well as bold white markings. Prior to the discovery of the W allelic series, many of these patterns were described by the term sabino, which is still used by some breed registries.
Catherine Feuillet is a French geneticist who is currently the Chief Scientific Officer of Inari Agriculture, a Cambridge MA based biotechnology company. Feuillet earned a PhD in plant molecular biology on the isolation and characterization of genes involved in wood formation in eucalyptus trees. She started to work on the genetics of disease resistance in wheat in 1994 during her post-doctoral studies at the Swiss Federal Institute for Agroecology. She then moved as a junior group leader to the University of Zurich where she investigated the molecular basis of fungal disease resistance in wheat and in barley and cloned the first leaf rust resistance gene from wheat. In 2004 she was hired as a research director at the Institut National de la Recherche Agronomique (INRA) in France to lead European and international projects on wheat genomics.
Ann Trommershausen Bowling was an American scientist who was one of the world's leading geneticists in the study of horses, conducting research in the areas of molecular genetics and cytogenetics. She was a major figure in the development of testing to determine animal parentage, first with blood typing in the 1980s and then DNA testing in the 1990s. She later became known for her studies of hereditary diseases in horses and equine coat color genetics, as well as research on horse evolution and the development of horse breeds. She studied the population genetics of feral horses, did considerable work to help preserve the Przewalski's horse, and was one of the founding members of the international project to map the horse genome. She was an adjunct professor at the University of California, Davis (UCD), and at the time of her death in 2000 was the executive associate director of the Veterinary Genetics Laboratory (VGL) there. Her unexpected death on December 8, 2000, at age 57 was attributed to a massive stroke.
