Chapter 14 Vocabulary

allele

Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.

amniocentesis

A technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus.

carrier

In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is generally phenotypically normal for the disorder but can pass on the recessive allele to offspring.

character

An observable heritable feature that may vary among individuals

chorionic villus sampling (CVS)

A technique associated with prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus.

codominance

The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways

complete dominance

The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

dihybrid

An organism that is heterozygous with respect to two genes of interest.

dihybrid cross

A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters).

dominant allele

An allele that is fully expressed in the phenotype of a heterozygote.

epistasis

A type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene

F1 generation

The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.

F2 generation

The offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generation.

genotype

The genetic makeup, or set of alleles, of an organism

heterozygous

Having two different alleles for a given gene

homozygous

Having two identical alleles for a given gene

hybridization

In genetics, the mating, or crossing, of two true-breeding varieties

incomplete dominance

The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele

law of independent assortment

Mendel's second law, stating that each pair of alleles segregates independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes

law of segregation

Mendel's first law, stating that the two alleles in a pair separate from each other into different gametes during gamete formation

monohybrid

An organism that is heterozygous with respect to a single gene of interest.

monohybrid cross

A cross between two organisms that are heterozygous for the single character being followed (or the self-pollination of a heterozygous plant).

P generation

The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance

pedigree

A diagram of a family tree with conventional symbols, showing the occurrence of heritable characters in parents and offspring over multiple generations

phenotype

The observable physical and physiological traits of an organism, which are determined by its genetic makeup.

pleiotropy

The ability of a single gene to have multiple effects

Punnett square

A diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype.

recessive allele

An allele whose phenotypic effect is not observed in a heterozygote

testcross

Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype

trait

One of two or more detectable variants in a genetic character

true-breeding

Referring to organisms that produce offspring of the same variety over many generations of self-pollination.

wild type

The phenotype most commonly observed in natural populations; also refers to the individual with that phenotype.

multifactorial

a phenotypic character that is influenced by multiple genes and environmental factors.

polygenic inheritance

A single phenotypic character that is a result of several genes