Genetics

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Addition rule

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The principle that the probability that any one of a set of mutually exclusive events is realized equals the sum of the probabilities of the separate events

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Albinism

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Absence of melanin pigment is the iris, skin, and hair of an animal; absence of chlorophyll in plants

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Allele

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Any of the alternative forms of a given gene

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Antibody

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A blood protein produced in response to a specific antigen and capable of binding with the antigen

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Backcross

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The cross of an F1 heterozygote with a partner that as the same genotype as one of its parents

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Carrier

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A heterozygote for a recessive allele

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Codominant

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Refers to phenotypes in which the presence of both alleles in heterozygous genotypes can be detected

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Complementation

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The phenomenon in which two recessive mutations with similar phenotypes result in a wildtype phenotype when both are heterozygous in the same genotype; means that the mutations are in different genes

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Complementation group

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a group of mutations that fail to complement one another

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Complementation test

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A genetic test to determine whether two mutations are alleles (are present in the same functional gene)

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Dominant trait

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Refers to an allele whose presence in a heterozygous genotype results in a phenotype characteristic of the allele

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Epistasis

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A term referring to an interaction between nonallelic genes in their effects on a trait. Generally, means any type of interaction in which the genotype at one locus affects the phenotypic expression of the genotype at another locus. In a more restricted sense, it refers to a situation in which the genotype at one locus determines the phenotype in such a way as to mask the genotype present at a second locus

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F1 generation

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The first generation of descent from a given mating

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F2 generation

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The second generation of decent from a given mating, produced by intercrossing or self-fertilizing F1 organisms

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Gamete

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A mature reproductive cell, such as sperm or egg in animals

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Gel electrophoresis

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A technique to separate molecules on the basis of their different rates of movement in response to an applied electric field, typically though a gel

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Gene

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The heredity unit defined experimentally by the complementation test. At the molecular level, a region of DNA containing genetic information, usually transcribed into an RNA molecule that is processed and either functions directly or is translated into a polypeptide chain; a gene can mutate to carious forms called alleles

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Genotype

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The genetic constitution of an organism or virus, typically with respect to one or a few genes of interest, as distinguished from its appearance, or phenotype

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Heterozygous

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Carrying dissimilar alleles of one of more genes; not homozygous

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Homozygous

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Having the same allele of a gene in homologous chromosomes

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Huntington disease

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Dominantly degeneration of the neuromuscular system, with onset in middle age

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Hybrid

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An organism produced by the mating of genetically unlike parents; also, a duplex nuclei acid molecule produced pf strands derived from different sources

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Incomplete Dominance

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Condition in which the phenotype of a heterozygous genotype is intermediate between the phenotypes of the homozygous genotype

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Independent assortment

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Random distribution of unlinked genes into gametes, as with genes in different (nonhomologous) chromosomes or genes that are so far apart on a single chromosome that the recombination frequency between them is 1/2

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Mendelian genetics

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The mechanism of inheritance in which the statistical relations between the distribution of traits in successive generations result from (1) particulate hereditary determinants (genes), (2) random union of gametes, and (3) segregation of unchanged hereditary determinants in the reproductive cells

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Multiple alleles

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The presence, in a population, of more than two alleles of a gene

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Multiplication Rule

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The principle that the probability that all of a set of independent events are realized simultaneously equals the product of the probabilities of the separate events

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Mutant Screen

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A type of genetic experiment in which the geneticist seeks to isolate multiple new mutations that affect a particular trait

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P1 generation

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The parents used in a cross, or the original parents in a series of generations; also called the P generation if there is no chance of confusion with the grandparents or more remote ancestors

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Pedigree

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A diagram representing the familial relationships among relatives

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Penetrance

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The proportion of organisms having a particular genotype that actually express the corresponding phenotype. If the phenotype is always expressed, is complete; otherwise, it is incomplete

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Phenotype

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The observable properties of a cell or an organism, which result from the interaction of the genotype and the environment

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Punnett Square

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A cross-multiplication square used for determining the expected genetic outcome of a mating

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Recessive trait

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Refers to an allele, or the corresponding phenotypic trait, expressed only in homozygotes

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Reciprocal cross

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A cross in which the sexes of the parents are the reverse of those in another cross

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Segregation

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Separation of the members of a pair of alleles into different gametes in meiosis

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Sib/ Sibling

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A brother or sister, each having the same parents

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Sibship

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A group of brothers and sisters

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Testcross

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A cross between a heterozgote and a recessive homozygote, resulting in progeny in which each phenotypic class represents a different genotype

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Transmission genetics

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The processes by which genes are passed from one generation to the next

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True-breeding

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Refers to a strain, breed, or variety of organism that yields progeny like itself; homozygous

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Variable expressivity

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Differences in the severity of expression of a particular genotype

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Wildtype

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The most common phenotype or genotype in a natural population; also, a phenotype or genotype arbitrarily designated as a standard for comparison

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Zygote

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The product of fusion of a female gamete and a male gamete in sexual reproduction; a fertilized egg