Unit 5 Chapter 11

Trait

One of two or more detectable variants in a genetic disorder

True-breeding

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

Hybridization

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

P generation

The true- breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance; P stands for “parental”

F1 generation

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

F2 Generatiion

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

Alleles

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

Dominant allele

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

Recessive allele

An allele whose phenotypic effect is not observed in a heterozygote.

Law of segregation

Mendel’s first law, stating that the two alleles in a pair segregate (separate from each other) into different gametes during gamete formation.

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.

Homozygous

Having two identical alleles for a given gene.

Heterozygous

Having two different alleles for a given gene.

Phenotype

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

Monohybrid

An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles are monohybrids.

For Example., parents of genotypes AA and aa produce a monohybrid of genotype Aa.

Monohybrid cross

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

Dihybrid

An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents double homozygous for different alleles are dihybrids.

For Example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.

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).

Law of independent assortment

Mendel’s second law, stating that each pair of alleles segregates, or assorts, 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.

Complete dominance

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

Incomplete dominance

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

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.

Pleiotroypy

The ability of a single gene to have multiple effects.

Polygenic inheritance

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

Multifactorial

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

Pedigree

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

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 hte disorder but can pass on the recessive allele to offspring.