Mendel and the Gene Idea – Key Vocabulary

These flashcards summarize essential vocabulary from the lecture on Mendelian genetics, covering foundational terms, laws, extensions to complex inheritance, human genetic disorders, and genetic testing techniques.

Blending hypothesis

Early idea that parental traits mix in offspring like paint; rejected by Mendel’s work.

Particulate hypothesis

Concept that parents pass on discrete heritable units (genes) that retain their identity.

Character

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

Trait

Each variant of a character, for example purple vs. white flowers.

True-breeding

Organisms that produce offspring identical to themselves for a given trait when self-pollinated.

Hybridization

Mating (crossing) of two contrasting true-breeding varieties.

P generation

The true-breeding parental generation in a genetic cross.

F₁ generation

First filial generation; hybrid offspring of the P generation.

F₂ generation

Offspring resulting from self- or cross-pollination of F₁ individuals.

Law of Segregation

Two alleles for a gene separate during gamete formation, so each gamete receives only one allele.

Dominant allele

Allele that determines phenotype in a heterozygote; masks recessive allele.

Recessive allele

Allele whose phenotypic effect is not observed in a heterozygote.

Allele

Alternative version of a gene found at the same locus on homologous chromosomes.

Locus

Specific physical location of a gene on a chromosome.

Homozygous

Having two identical alleles for a gene (e.g., PP or pp).

Heterozygous

Having two different alleles for a gene (e.g., Pp).

Genotype

Genetic makeup of an organism for a trait (e.g., PP, Pp, pp).

Phenotype

Observable physical and physiological traits of an organism.

Punnett square

Diagram that predicts allele composition of offspring from a cross.

Testcross

Crossing an individual showing the dominant phenotype with a homozygous recessive to determine genotype.

Monohybrid cross

Cross between heterozygotes for a single character (e.g., Pp × Pp).

Law of Independent Assortment

Each pair of alleles segregates independently of other allele pairs during gamete formation (applies to genes on different chromosomes or far apart on same chromosome).

Dihybrid cross

Cross between individuals heterozygous for two characters (e.g., YyRr × YyRr).

Multiplication rule

Probability that independent events will occur together equals the product of their probabilities.

Addition rule

Probability that any one of two mutually exclusive events occurs equals the sum of their probabilities.

Complete dominance

Heterozygote phenotype identical to dominant homozygote.

Incomplete dominance

Heterozygote phenotype intermediate between two homozygotes (e.g., pink snapdragons).

Codominance

Both alleles affect phenotype in distinguishable ways (e.g., ABO blood IAIB type).

Tay-Sachs disease

Lethal disorder where dominance depends on observation level: recessive organismally, incompletely dominant biochemically, codominant molecularly.

Multiple alleles

Gene with more than two allele forms in population (e.g., ABO IA, IB, i).

ABO blood group

Human red-cell phenotype determined by three alleles producing A, B, AB, or O types.

Pleiotropy

Single gene influences multiple phenotypic traits (e.g., sickle-cell or cystic fibrosis alleles).

Epistasis

Gene at one locus alters phenotypic expression of gene at another locus (e.g., Labrador coat color).

Polygenic inheritance

Additive effect of two or more genes on a single phenotype (e.g., human skin color).

Quantitative character

Trait that varies along a continuum, usually due to polygenic inheritance.

Multifactorial trait

Phenotype influenced by many genes and environmental factors (e.g., heart disease).

Carrier

Heterozygote that is phenotypically normal but transmits recessive allele for a disorder.

Pedigree

Family tree showing trait inheritance across generations.

Albinism

Recessive disorder causing lack of pigment in skin, hair, eyes.

Cystic fibrosis

Common lethal recessive disorder; defective chloride channels cause mucus buildup.

Sickle-cell disease

Recessive disorder from mutant hemoglobin; causes sickled red cells and health issues.

Sickle-cell trait

Heterozygous condition; generally healthy and offers malaria resistance.

Achondroplasia

Dominant disorder causing dwarfism.

Huntington’s disease

Late-onset dominant neurodegenerative disorder, fatal after symptom onset.

Amniocentesis

Prenatal test sampling amniotic fluid for chromosomal and genetic analysis.

Chorionic villus sampling (CVS)

Prenatal test removing placental tissue for rapid genetic testing.

Newborn screening

Routine testing of infants for certain genetic disorders (e.g., PKU).

Consanguineous mating

Mating between close relatives; increases risk of recessive disorders.