Mendelian Genetics Vocabulary

Vocabulary flashcards covering Mendelian genetics principles, monohybrid and dihybrid crosses, genetic terminology, chromosome theory, molecular basis of mutant phenotypes, pedigree analysis, and statistical evaluation.

Monohybrid Cross

A genetic cross between two individuals considering a single trait controlled by one gene with two alleles, typically between two heterozygotes.

Dihybrid Cross

A genetic cross between two individuals considering two distinct traits controlled by two separate genes, both heterozygous in each parent, yielding a classic $9:3:3:1$ F2 phenotypic ratio.

Law of Segregation

Mendel's 1st Law stating that during gamete formation, the two alleles for a gene separate from each other during meiosis so that each gamete carries only one allele for each trait.

Law of Independent Assortment

Mendel's 2nd Law stating that alleles of different genes assort independently of one another into gametes during meiosis.

Law of Dominance

Mendel's 3rd Law stating that in a heterozygote, one allele masks the phenotypic expression of another allele at the same locus.

Mendel's Laws of Inheritance

The foundational principles of inheritance comprising the Law of Segregation, the Law of Independent Assortment, and the Law of Dominance.

Particulate Unit Factors

Mendel's term for the basic units of heredity (now known as genes and alleles) that are passed unchanged from generation to generation.

Reciprocal Cross

A pair of genetic crosses where the phenotypes of the male and female parents are reversed to demonstrate whether a trait is sex-dependent.

Testcross

A cross between an individual displaying a dominant phenotype (with an unknown genotype) and a homozygous recessive individual to reveal the unknown genotype.

Phenotype

The observable physical expression or measurable trait of an organism determined by its genetic makeup and environment.

Genotype

The specific genetic makeup or allelic composition of an individual for a given trait.

Homozygous

An organism or cell having two identical alleles for a specific gene (e.g., $DD$ or $dd$).

Heterozygous

An organism or cell having two different alleles for a specific gene (e.g., $Dd$).

Pedigree Symbols

Standardized symbols used in pedigree charts where circles denote females, squares denote males, shaded figures denote affected individuals, and 'P' indicates the proband.

Proband

The first affected family member who seeks medical attention for a genetic disorder, designated by an arrow in a pedigree chart.

Penetrance

The proportion of individuals carrying a particular genetic variant who express the corresponding clinical or physical phenotype.

Chromatin

The granular-appearing nucleoprotein structures stained by dye in dividing cells, named by Walter Flemming in 1879 from the Greek word for color.

Chromosome Theory of Inheritance

The principle independently proposed by Sutton and Boveri asserting that genes are located on chromosomes and that chromosome separation during meiosis provides the physical basis for segregation and independent assortment.

Starch-Branching Enzyme (SBE)

An enzyme catalyzed by the dominant allele $R$ that converts unbranched starch to branched starch during pea seed maturation; its absence in recessive $r$ mutants leads to unbranched starch accumulation, higher osmotic pressure, and wrinkled seeds.

Null Hypothesis

A statistical hypothesis stating that there is no real difference between observed and expected data, and any observed deviation is due entirely to random chance.

Chi-Square ($\chi^2$) Analysis

A statistical goodness-of-fit test used to evaluate the hypothesis that observed deviations from predicted genetic outcomes are due solely to chance.