Biology: The Unity and Diversity of Life - Chapter 13: Observing Patterns in Inherited Traits

Vocabulary practice flashcards covering Mendelian and non-Mendelian inheritance patterns, genetic terminology, gene interactions, epigenetics, and continuous variation from Chapter 13.

Cystic Fibrosis (CF)

The most common fatal genetic disorder in the United States, caused by mutations in the CFTR gene that lead to clogged airways, hampered sperm flow, impaired nutrient duct function, and chronic bacterial infections, with most sufferers dying before age 30.

CFTR Protein

A membrane transport protein that pumps chloride ions out of epithelial cells so water follows by osmosis to keep cell sheets moist; it also functions as an immune receptor that binds bacteria to trigger endocytosis.

$$\Delta F508$$

A deletion mutation of three base pairs that prevents proper membrane trafficking of the CFTR protein, resulting in abnormally dry epithelial surfaces and thick, obstructive mucus.

Gene

A heritable unit of information discovered by Gregor Mendel that resides at a specific locus on a chromosome.

Locus

The specific physical location of a gene on a chromosome.

Genotype

The particular set of alleles that an individual carries on its chromosomes.

Phenotype

The observable physical, physiological, and behavioral traits of an individual, determined by genotype and environmental influences.

Homozygous

A condition in which an individual carries two identical alleles of a given gene (such as $PP$ or $pp$).

Heterozygous

A condition in which an individual carries two nonidentical alleles of a given gene (such as $Pp$).

Hybrid

A heterozygous offspring resulting from a cross between two individuals that breed true for different forms of a trait.

Dominant Allele

An allele whose phenotypic effect masks the effect of a recessive allele paired with it in a heterozygote.

Recessive Allele

An allele whose phenotypic effect is fully masked when paired with a dominant allele on the homologous chromosome.

Punnett Square

A grid used to calculate the theoretical probability of different genotypes and phenotypes among the offspring of a genetic cross.

Testcross

A breeding experiment designed to determine whether an individual displaying a dominant trait is homozygous dominant or heterozygous by crossing it with a homozygous recessive individual.

Monohybrid Cross

A cross checking for dominance relationships between two alleles at a single locus, typically carried out between true-breeding parents or identical $F_1$ heterozygotes ($Pp \times Pp$).

Law of Segregation

Mendel's principle stating that diploid cells carry pairs of genes on homologous chromosomes, and the two genes of each pair separate during meiosis so that each gamete receives only one.

Dihybrid Cross

A cross testing dominance relationships between alleles at two distinct gene loci, producing a characteristic $9:3:3:1$ phenotypic ratio in the $F_2$ generation.

Law of Independent Assortment

Mendel's principle stating that gene pairs on homologous chromosomes are distributed into gametes independently of other gene pairs during meiosis.

Linkage Group

A group of genes located very close to one another on the same chromosome that tend to be inherited together during meiosis rather than assorting independently.

Codominance

An inheritance pattern in which two nonidentical alleles of a gene are both fully expressed in heterozygotes, meaning neither allele is dominant or recessive (e.g., the $AB$ blood type).

Multiple Allele System

A gene system characterized by the presence of three or more distinct alleles persisting in a population, such as the ABO blood type alleles.

Incomplete Dominance

An inheritance pattern in which one allele is not fully dominant over another, resulting in an intermediate heterozygous phenotype and an $F_2$ phenotypic ratio of $1:2:1$ (e.g., pink snapdragons from red and white parents).

Polygenic Inheritance

An inheritance mode in which the alleles of two or more separate genes determine a single phenotypic trait.

Epistasis

A form of polygenic interaction wherein the product of one gene masks or suppresses the expression and effect of an entirely different gene (e.g., coat color in Labrador retrievers).

Pleiotropy

A condition in which a single gene influences multiple, seemingly distinct phenotypic traits, as observed in cystic fibrosis, sickle-cell anemia, and Marfan syndrome.

Marfan Syndrome

A potentially fatal pleiotropic disorder caused by a mutation in the fibrillin gene that leads to tall stature, thin limbs, and defective elastic tissue causing the aorta wall to stretch, leak, and potentially rupture during exercise.

Epigenetics

The study of interactions between traits and the environment that produce heritable changes in gene expression through mechanisms such as DNA methylation and chromatin modification without altering the DNA sequence.

Continuous Variation

A range of small, incremental phenotypic differences in a trait across individuals in a population, typical of polygenic traits influenced by environmental factors and forming a bell curve.

Bell Curve

A symmetrical, bell-shaped graph showing the frequency distribution of a continuously varying trait across a population.

Short Tandem Repeats

Short sequences of DNA repeated in tandem that expand or contract rapidly compared to standard mutation rates, creating novel alleles that contribute to continuous phenotypic variation.