BIOL 207 Lecture 6 - Foundations in Classic Genetics (Terms)

Alleles

Different variants of the same gene that exist at the same locus

Homozygous

An organism containing pair of homologous chromosomes with identical alleles at the same gene locus

Heterozygous

An organism containing pair of homologous chromosomes with one wild type allele and one mutant or differing allele at the same gene locus

Allelic Series

The known mutant alleles for a given gene, plus its wild type allele

Null Mutation

A mutation of an allele that produces no functional expression, resulting in a phenotype that contains an absence of expression (colour, trait, etc.)

Compound Heterozygotes (Heteroallelic/Transheterozygous)

An organism with two separate mutant alleles that are distinct from one another, not containing any wild type alleles

Hemizygous

An organism containing only one copy of a gene at its locus such that there is only one allele

True-Breeding

Individuals that when crossed with each other will always give rise to offspring of the same phenotype, generally being homozygous for the allele causing the trait

Polygenic

Complex traits linked to multiple genes

Monogenic

Simple traits linked to a single gene

Complete Dominance

An dominant allele’s phenotypic expression always and fully having priority over its recessive allele in a heterozygote

Haplosufficiency

An allele descriptor where only one functional copy of the allele is sufficient for a wild type phenotype to be expressed

Incomplete Dominance (Semi-Dominance)

An dominant allele’s phenotypic expression showing an intermediate phenotype when in conjunction with another mutated allele in the heterozygote, showing the blended phenotype of two homozygous parents

Haploinsufficiency

An allele descriptor where only one functional copy of the allele is not sufficient for a wild type phenotype to be expressed, and thus the offspring needs to be homozygous dominant for the wild type allele

Codominance

Two dominant alleles’ phenotypic expression showing both phenotypes of the alleles expressed in an unblended way

Sickle Cell Anemia

A point mutation in hemoglobin that mutates an Hb^A to an Hb^S, giving rise to sickle-shaped cells in addition to regular blood cells

Heterozygous Advantage

A resistance or advantage gained by an organism from containing heterozygous alleles instead of homozygous, giving it protection against diseases and other elements

Dominant Negative Effect

An effect in which the gene product from a mutant allele interferes with the gene product from the wild type allele, blocking or altering wild type function

Gain-of-Function Effect

An effect in which a mutant allele acquires a new property not present in the wild type allele, causing a new phenotype

Amorphs

A form of mutant allele defect in which there is a complete loss of function, synonymous with a null mutation

Hypomorphs

A form of mutant allele defect in which the allele is still partially functional, but not at the level of the wild type allele, known as a “partial loss of function” or “leaky”

Porphyrias

A group of diseases affecting heme production due to amorphic or hypomorphic alleles that encode heme biosynthetic pathways

Hypermorphs

A form of mutant allele defect in which the mutant allele gives the gene a higher level of expression than the wild type allele, a type of “gain-of-function” mutation

Myostatin

A repressor of muscle growth in sheep and cattle

Neomorph

A form of mutant allele defect in which the mutant allele has acquired a changed or new function that a wild type allele does not have, a type of “gain-of-function” mutation

Oncogenes

Neomorphic alleles of cancer genes, comprised of cancer gene relocation to another chromosome or formation of a hybrid oncogene

Antimorph

A form of mutant allele defect in which the allele is no longer active, but is also capable of overriding the function of the wild type allele in a heterozygous setting, used interchangeably with “dominant negative”

Complementation Tests

A tool to categorize mutants by determining whether their combination makes a complement phenotype, thus concluding that they are mutant in the same or different gene loci

Non-Allelic Mutations

Mutations that complement, found on different gene loci and thus not being alleles of the same gene

Allelic Mutations

Mutations that are non-complementing, found on the same gene loci and being alleles of the same gene