Chapter 14: Mendel and the Gene Idea

Vocabulary flashcards covering Mendelian genetics, laws of inheritance, probability rules, non-Mendelian gene interactions, and human genetic disorders based on Chapter 14 of Campbell Biology.

Character

A heritable feature that varies among individuals, such as flower color in pea plants.

Trait

Each specific variant for a character, such as purple or white color for flowers.

True-breeding

Organisms that produce offspring of the same variety over many generations when they self-pollinate.

Hybridization

The mating or crossing of two contrasting, true-breeding varieties.

P Generation

The true-breeding parental generation from which hybrid offspring are produced.

$F_1$ Generation

The first filial hybrid offspring derived from a cross between the parental ($P$) generation.

$F_2$ Generation

The second filial generation of offspring produced when $F_1$ individuals self-pollinate or cross-pollinate with other $F_1$ hybrids.

Alleles

Alternative versions of a gene that account for variations in inherited characters.

Locus

The specific physical site or sequence location where a gene resides on a chromosome.

Dominant Allele

An allele that determines the organism's physical appearance when two different alleles are present at a locus.

Recessive Allele

An allele that has no noticeable effect on an organism's appearance when present alongside a dominant allele at a locus.

Law of Segregation

Mendel's first law stating that the two alleles for a heritable character separate during gamete formation and end up in different gametes.

Punnett Square

A handy diagrammatic device used to predict the allele combinations resulting from a cross between individuals of known genetic makeup.

Homozygote

An organism that possesses two identical alleles for a gene controlling a particular character (homozygous).

Heterozygote

An organism that possesses two different alleles for a gene controlling a particular character (heterozygous); not true-breeding.

Phenotype

An organism's observable physical traits, internal anatomy, physiology, and behavior.

Genotype

The complete genetic makeup or set of alleles of an organism.

Testcross

Breeding an individual of dominant phenotype but unknown genotype with a homozygous recessive individual to reveal the mystery parent's genotype.

Monohybrids

Offspring that are heterozygous for the single character being followed in a genetic cross.

Monohybrid Cross

A cross between individuals that are both heterozygous for one specific character.

Dihybrids

Offspring that are heterozygous for two distinct characters being tracked in a genetic cross.

Dihybrid Cross

A cross between $F_1$ dihybrids used to determine whether two characters are transmitted to offspring together as a unit or independently.

Law of Independent Assortment

Mendel's second law stating that each pair of alleles segregates independently of any other pair of alleles during gamete formation, applying to nonhomologous chromosomes or genes far apart on the same chromosome.

Multiplication Rule

A probability rule stating that the probability of two or more independent events occurring simultaneously is the product of their individual probabilities.

Addition Rule

A probability rule stating that the probability of any one of two or more mutually exclusive events occurring is the sum of their individual probabilities.

Complete Dominance

A degree of dominance wherein the heterozygous phenotype is identical to that of the homozygous dominant individual.

Incomplete Dominance

A degree of dominance in which the phenotype of $F_1$ hybrids is intermediate between the two homozygous parental phenotypes.

Codominance

A condition in which two dominant alleles affect the phenotype in separate, distinguishable ways in heterozygotes.

Tay-Sachs Disease

A fatal inherited disorder caused by a dysfunctional enzyme leading to lipid accumulation in the brain; recessive at the organismal level, incompletely dominant biochemically, and codominant molecularly.

Polydactyly

A condition of having extra fingers or toes caused by a dominant allele, present in only $1$ out of $400$ babies in the United States despite its dominant inheritance.

Pleiotropy

The property of a single gene affecting multiple, distinct phenotypic characters.

Epistasis

A type of gene interaction where the phenotypic expression of a gene at one locus alters the expression of a gene at a second locus.

Quantitative Characters

Heritable features that vary along a continuum within a population rather than presenting as distinct alternative categories.

Polygenic Inheritance

An additive effect of two or more genes on a single phenotypic character, typically responsible for continuous quantitative variation.

Multifactorial

Referring to phenotypic traits influenced by multiple genes acting in combination with environmental influences.

Pedigree

A diagrammatic family tree describing the occurrence and inheritance of a trait across generations.

Carriers

Heterozygous individuals who carry a recessive disease-causing allele but are phenotypically normal.

Consanguineous Matings

Matings between close biological relatives that elevate the probability that offspring will inherit rare, harmful recessive alleles.

Cystic Fibrosis

The most common lethal genetic disease in the United States among people of European descent ($1$ in $2{,}500$), caused by defective or absent chloride transport channels in plasma membranes.

Sickle-Cell Disease

A recessively inherited blood disorder affecting $1$ out of $400$ African Americans, caused by the substitution of a single amino acid in hemoglobin.

Achondroplasia

A form of dwarfism caused by a rare dominant allele ($Dd$) that produces the dwarf phenotype in heterozygotes.

Huntington's Disease

A lethal, degenerative disease of the nervous system caused by a dominant allele with no obvious phenotypic symptoms until age $35$ to $40$.

Amniocentesis

A prenatal diagnostic procedure in which a needle is inserted into the uterus to withdraw amniotic fluid bathing the fetus for genetic and biochemical testing.

Chorionic Villus Sampling (CVS)

A prenatal diagnostic procedure wherein a sample of placental tissue is extracted through the cervix via a suction tube for immediate karyotyping and genetic analysis.

Phenylketonuria (PKU)

A recessively inherited metabolic condition routinely screened for in newborns, striking $1$ out of every $10{,}000\text{--}15{,}000$ births in the United States.