Chapter 9: Patterns of inheritance Bio-102

Alleles

An alternative version of a gene.

Codominant

Expressing two different alleles of a gene in a heterozygote.

Dihybrid cross

A mating of individuals differing at two genetic loci.

Dominant allele

In a heterozygote, the allele that determines the phenotype with respect to a particular gene; the dominant version of a gene is usually represented with a capital italic letter (e.g., F ).

Genotype

The genetic makeup of an organism.

Heterozygous

Having two different alleles for a given gene.

Homozygous

Having two identical alleles for a given gene.

Hybrids

The offspring of parents of two different species or of two different varieties of one species; the offspring of two parents that differ in one or more inherited traits; an individual that is heterozygous for one or more pairs of genes.

Incomplete dominance

A type of inheritance in which the phenotype of a heterozygote (Aa) is intermediate between the phenotypes of the two types of homozygotes (AA and aa).

Law of independent assortment

A general rule of inheritance, first proposed by Gregor Mendel, that states that when gametes form during meiosis, each pair of alleles for a particular character segregates (separates) independently of each other pair.

Law of segregation

A general rule of inheritance, first proposed by Gregor Mendel, that states that the two alleles in a pair segregate (separate) into different gametes during meiosis.

Linked genes

Genes located close enough together on a chromosome that they are usually inherited together.

Locus

The particular site where a gene is found on a chromosome. Homologous chromosomes have corresponding gene loci.

Monohybrid cross

A mating of individuals that are heterozygous for the character being followed.

Phenotype

The expressed traits of an organism.

Pleiotrophy

The control of more than one phenotypic character by a single gene.

Polygenic inheritance

The additive effect of two or more genes on a single phenotypic character.

Recessive allele

In heterozygotes, the allele that has no noticeable effect on the phenotype; the recessive version of a gene is usually represented with a lowercase italic letter (e.g.,f).

Sex-linked gene

A gene located on a sex chromosome.

testcross

The mating between an individual of unknown genotype for a particular character and an individual that is homozygous recessive for that same character.