Chapter 8: Patterns of Inheritance

Vocabulary terms covering Mendelian genetics, inheritance laws, and extensions of Mendelian principles based on lecture notes for BIO 1111.

Genetics

The study of heredity.

Pisum sativum

The species of garden pea used by Mendel as the primary model system to study inheritance.

True-breeding

Organisms that always produce offspring that look like the parent.

Hybridizations

The process of mating two true-breeding individuals that have different traits.

P generation

The parental generation; the plants used in first-generation crosses.

F1 generation

The first filial generation, consisting of offspring from the P generation plants.

F2 generation

The second filial generation, consisting of offspring from the F1 generation plants.

Trait

A variation in the physical appearance of a heritable characteristic.

Dominant traits

Traits that are inherited unchanged in a hybridization; they can conceal the presence of another trait.

Recessive traits

Traits that become latent or disappear in the offspring of a hybridization but reappear in the progeny of the hybrid offspring.

Genes

Specific nucleotide segments located on chromosomes that determine specific characteristics by coding for specific proteins.

Alleles

Gene variants that arise by mutation and exist at the same relative locations on homologous chromosomes.

Locus

The specific location of a gene on a chromosome.

Phenotype

The physical appearance or observable traits expressed by an organism.

Genotype

An organism’s underlying genetic makeup, often represented by pairs of letters such as $YY$ or $yy$.

Homozygous

A genotype having two identical alleles on homologous chromosomes (e.g., $YY$ or $yy$).

Heterozygous

A genotype having two different alleles for a specific gene (e.g., $Yy$).

Mendel’s law of dominance

In a heterozygote ($Aa$), one trait will conceal the presence of another trait for the same characteristic.

Monohybrid cross

Fertilization between two true-breeding parents that differ by only one specific characteristic.

Punnett square

A tool used to predict all possible genotypic and phenotypic outcomes of random fertilization events and their expected frequencies.

Law of Segregation

Alleles must segregate equally into gametes during meiosis so that each gamete is equally likely to receive either one of the two alleles.

Test cross

A cross between a dominant-expressing organism and a homozygous recessive organism to determine the dominant organism's genotype.

Law of independent assortment

Genes do not influence each other regarding the sorting of alleles into gametes, and every possible combination of alleles is equally likely.

Incomplete Dominance

An inheritance pattern where the heterozygote expresses an intermediate phenotype between the dominant and recessive phenotypes, such as pink flowers ($C^RC^W$).

Codominance

A situation where both alleles for the same characteristic are simultaneously expressed in the heterozygote, such as the human AB blood group.

Wild type

The most common phenotype or genotype in a natural population, often abbreviated as $+$.

X-linked

A gene present on the X chromosome but not the Y chromosome.

Hemizygous

The presence of only one allele for any X-linked characteristic, as observed in human males ($XY$).

Linkage

The tendency for genes located physically close to each other on the same chromosome to be inherited together as a pair.

Polygenic inheritance

Characteristics that depend on the combined effects of numerous genes, such as human skin color or height.

Epistasis

A genetic interaction where one gene masks or interferes with the expression of another gene.