Glossary
allele:
one of the inherited forms of a particular gene or stretch of DNA. An animal carries two alleles for each gene, one from each parent.
autosomal:referring to chromosomes other than the sex chromosome.
centiMorgan (cM):a unit of measurement that describes how tightly linked two points on a chromosome are—that is, how likely they will be separated by crossover during meiosis (1 cM equals 1 percent recombination). One hundred centiMorgans, or one Morgan, takes its name from biologist Thomas Hunt Morgan, who first observed the crossover phenomenon in the early part of this century.
chromosomes:discrete collections of DNA that contain the information that is passed from one generation to the next. Each animal species has a characteristic number of chromosomes.
coinheritance:the passing along of two traits (or, on a genetic level, of two segments of DNA) together. Loci that are tightly linked have a high probability of being coinherited.
crossover:a process that occurs during the creation of eggs and sperm in which chromosomes exchange segments of DNA, enhancing the possible variability in offspring.
diploid:containing a full set of chromosomes, half of which were donated by the mother and the other half from the father.
economic trait loci (ETL):loci that code for traits of economic interest to producers (litter size, disease resistance, percent lean, etc.).
electrophoresis:
a laboratory process that separates molecules based on their electrical charge.
epistasis:the process in which one gene causes another (other than its allele) to not be expressed.
genes:stretches of DNA within a chromosome that contain specific information needed by the cell to make the proteins that control the growth, development and function of the organism.
genome:the set of DNA molecules that specify the inherited characteristics of an animal. With a few minor exceptions, every cell in an animal's body carries the entire genome within its nucleus.
genotype:the genetic makeup of an organism.
genotyping:the process of identifying which alleles an organism carries for a specific trait or traits.
halothane gene test (Hal):a genetic test for the presence of the gene that causes porcine stress syndrome (PSS).
haploid:containing half the normal number of chromosomes. Eggs and sperm are haploid.
heterosis:the tendency of crossbred organisms to be better than either of their parents.
heterozygosity:the degree to which a gene occurs in different forms in different animals.
linkage map:a map that describes the location of genes relative to other genes rather than as points on specific parts of specific chromosomes.
locus (loci):the location of a particular DNA segment on a chromosome.
major histocompatibility complex (MHC):a length of DNA that contains numerous genes involved in regulating the process by which the body distinguishes itself from invaders (bacteria, thorns, etc.).
marker:a portion of DNA that appears in more than one form in a population, the variations of which can be detected in the laboratory and so used to identify patterns of heredity.
marker-assisted selection (MAS):selection of animals for propagation or culling based on the presence or absence of genetic markers that are linked to desired or undesired characteristics.
meiosis:the process that creates haploid egg and sperm cells.
microsatellite:a stretch of DNA that contains a repeating nucleotide pattern, the length of which is polymorphic. Microsatellites are used as markers.
nucleotide:one of four similar molecules that, when linked together into DNA, create the code that determines an organism's inherited characteristics.
phenotype:the expressed characteristics of an organism. Not all genes of the genotype affect the phenotype.
polymerase chain reaction (PCR):a biochemical technique that allows laboratory workers to produce millions of copies of a relatively short (100-300 nucleotide) sequence of DNA. PCR is an invaluable technique for distinguishing which allele of a microsatellite marker is present in a blood or tissue sample.
polymorphism:one of the various forms of a gene.
PSS (porcine stress syndrome):a disorder of swine that can cause extreme reactions to stress and poor carcass quality.
quantitative trait loci (QTL):genes that contribute to the expression of a trait that is expressed on a continuum (e.g., weight gain).
recessive genes:genes that are not expressed in a particular organism. Even though these genes are silent for the time being, they can be passed along to—and expressed in—successive generations.
reference families:groups of related but genetically varied animals (usually three generations) which are used by genome mappers to create a linkage (cM) map.
resource family:a group of related animals that show characteristics of interest such as good marbling and large litter size, for which researchers have both genetic material and information about which of the related individuals exhibit the characteristic. Useful for mapping QTL and in developing markers for MAS.
restriction enzymes:proteins that cleave DNA at the site of a particular nucleotide sequence. Because they only work when their particular, recognizable sequence is present, restriction enzymes can be used to identify which form of a polymorphic DNA segment an animal has inherited.
restriction fragment length polymorphism (RFLP):a polymorphic DNA segment that influences how a DNA segment cleaves when treated with a restriction enzyme. RFLPs are used as markers.
SLA Types-major histocompatibility:a genetic test for determining the alleles of genes controlling immune responses.
translocations for boar:a genetic test for determining whether the physical relocation of chromosomal pieces has occurred.
Type I marker:see restriction fragment length polymorphism
Type II marker:see microsatellite
Variance:ranges in phenotype that result from genetic and environmental parameters.