USGS - science for a changing world

Ecosystems - Genetics and Genomics

Maps, Imagery, and Publications Hazards Newsroom Education Jobs Partnerships Library About USGS Social Media

Genetics and Genomics Glossary

The following glossary was obtained with permission from the following resource: Allendorf, F.W., and G. Luikart. 2007. Conservation and the Genetics of Populations. Blackwell Publishing. 642 pp.



SARA
See
Species at Risk Act of Canada.

selection coefficient
The reduction in relative fitness, and therefore genetic contribution to future generations, of one genotype compared to another.

selection differential
The difference the mean value of a quantitative trait found in a population as a whole compared to the mean value of the trait in the breeding population.

selective sweep
The rapid increase in frequency by natural selection of an initially rare allele that also fixes (or nearly fixes) alleles at closely linked loci thus reduces the genetic variation in a region of a chromosome.

sensitivity testing
A method used in population viability analyses where the effects of parameters on the persistence of populations are determined by testing a range of possible values for each parameter.

sequential Bonferroni correction
A method, similar to the Bonferroni correction, that is used to reduce the probability of a Type I statistical error when conducting multiple simultaneous tests.

sex chromosomes
Chromosomes that pair during meiosis but differ in the hererogametic sex.

sex-linked locus
A locus that is located on a sex chromosome.

sexual selection
Selection due to differential mating success either through competition for mates or mate choice.

shadow effect
A case usually caused by low marker polymorphism in markrecapture studies in which a novel capture is labeled as a recapture due to identical genotypes at the loci studied.

SINEs
Short interspersed nuclear elements.

single nucleotide polymorphism (SNP)
A nucleotide site (base pair) in a DNA sequence that is polymorphic in a population either due to transitions or transversions and can be used as a marker to assess genetic variation within and among populations. Usually only two alleles exist for a SNP in a population.

SMM
See
stepwise mutation model.

SNP
See
single nucleotide polymorphism.

species
A group of organisms with a high degree of physical and genetic similarity, that naturally interbreed among themselves and can be differentiated from members of related groups of organisms.

Species at Risk Act of Canada (SARA)
Legislation (passed in 2002) to prevent wildlife species from becoming extinct and secure the necessary actions for their recovery. It provides for the legal protection of wildlife species and the conservation of critical habitat.

species concepts
The ideas of what constitutes a species, such as reproductive isolation (BSC), or monophyly of a lineage (PSC).

species scale
The spatial scale encompassing an entire species’ distribution.

SSRs
Simple sequence repeats. See microsatellite.

stable polymorphism
A polymorphism that is maintained at a locus through natural selection.

stabilizing selection
Selection for a phenotype with a more intermediate state.

stepping stone model of migration
A model of migration in which the probability of migration between nearby or adjacent populations is higher than the probability of migration between distant populations.

stepwise mutation model (SMM)
A model of mutation in which the microsatellite allele length has an equal probability of either increasing or decreasing (usually by a single repeat unit, as in the strict one-step SMM).

stochastic
The presence of a random variable in determining the outcome of an event.

stock
A term generally used in fisheries management that refers to a population that is demographically independent and often represents a subunit (e.g., MU) of an ESU.

STR
Short tandem repeat. See microsatellite.

subpopulations
Groups within a population delineated by reduced levels of gene flow with other groups.

subspecies
A taxonomically defined subdivision within a species that is physically or genetically distinct, and often geographically separated.

sum rule
A statistical rule that states that the probability of ni mutually exclusive, independent events occurring is equal to the sum of the probabilities of each n event.

supergene
Allelic combinations found at closely linked loci that affect related traits and are inherited together. An example of a supergene is the major histocompatibility complex (MHC), which in humans contains more than 200 genes adjacently located over several megabases of sequence on chromosome 6.

supernumerary chromosome
A chromosome, often present in varying numbers, that is not needed for normal development, lacks functional genes, and does not segregate during meiosis. These small chromosomes, which are also called B chromosomes, are present in addition to the normal complement of functional chromosomes in an organism.

supportive breeding
The practice of removing a subset of individuals from a wild population for captive breeding and releasing the captive-born offspring back into their native habitat to intermix with wild-born individuals and increase population size or persistence.

sympatric
Populations or species that occupy the same geographic area.

synapomorphy
A shared derived trait between evolutionary lineages. A homology that evolved in an ancestor common to all species on one branch of a phylogeny, but not common to species on other branches.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

back to top

 

 

 

 

 

 

 

 

 

 

 

 

 

 

back to top

 

 

 

 

 

 

 

 

 

 

 

 

back to top

 

 

 

 

 

 

 

 

 

 

 

 

 

 

back to top

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://www.usgs.gov/ecosystems/genetics_genomics/\\afs\usgs.gov\www\www\htdocs\ecosystems\genetics_genomics\glossary_s.html
Page Contact Information: Ask USGS
Page Last Modified: Monday January 14 2013