Lecture 1: Mendel and the Gene Idea - Vocabulary Flashcards

A vocabulary set covering the key genetic concepts from Mendel’s genetics lecture, including genes, alleles, meiosis, inheritance laws, dominance patterns, pedigrees, and common genetic disorders.

Particulate hypothesis

Theory that parents pass on discrete heritable units (genes) to offspring.

Gene

Discrete heritable unit that encodes a trait; the basic unit of inheritance.

Allele

Alternative form of a gene at the same locus; variants of a gene.

Trait

A variant of a character expressed as a phenotype.

Phenotype

Observable physical form of a trait, determined by genes and environment.

Character

Heritable feature or attribute (often used interchangeably with trait in Mendelian context).

Dominate allele

Allele that determines phenotype when present, often masking the other allele.

Recessive allele

Allele whose effect is masked by a dominant allele in heterozygotes.

Pp

Heterozygous genotype for one gene (one dominant and one recessive allele).

Homozygous

Having two identical alleles for a given gene.

Heterozygous

Having two different alleles for a given gene.

Autosome

Any of the 22 non-sex chromosomes; carry most genes.

Sex chromosome

Chromosome determining sex (X and Y in humans; 23rd pair).

Diploid

Cell with two complete sets of chromosomes (2n).

Haploid

Cell with a single set of chromosomes (n).

Gamete

Haploid reproductive cell (egg or sperm) that combines during fertilization.

Fertilization

Union of two gametes to form a zygote.

Zygote

Fertilized egg; diploid cell (2n) resulting from fertilization.

Meiosis

Cell division that produces haploid gametes from diploid cells, includes two rounds of division.

Meiosis I

First division where homologous chromosomes separate.

Meiosis II

Second division where sister chromatids separate, producing haploid gametes.

Crossing over

Exchange of genetic material between homologous chromosomes during prophase I.

Synapsis

Pairing of homologous chromosomes during prophase I of meiosis.

3:1 ratio

Typical Mendelian phenotypic ratio in F2 for a single-gene cross (dominant to recessive).

Law of Segregation

Two alleles for a gene separate during gamete formation; each gamete carries one.

Law of Independent Assortment

Alleles of different genes assort independently during gamete formation.

P generation

Parental generation in Mendel’s crosses; true-breeding lines.

F1 generation

First filial generation; offspring of the P generation.

F2 generation

Second filial generation; offspring of F1 crosses or self-fertilization.

True-breeding

Line that, when self-fertilized, produces offspring identical for a trait.

Hybridization

Crossing two true-breeding varieties.

Monohybrid cross

Cross between two organisms heterozygous for a single gene (e.g., Pp × Pp).

Test cross

Cross between an unknown genotype and a homozygous recessive to determine genotype.

Dominant phenotype

Phenotype that masks the presence of a recessive allele in a heterozygote.

Recessive phenotype

Phenotype expressed only when two recessive alleles are present.

Complete dominance

One allele completely masks the other; two phenotypes observed.

Incomplete dominance

Heterozygote phenotype is intermediate between two homozygotes (e.g., pink from red and white).

Codominance

Both alleles equally visible in the phenotype (e.g., AB blood type).

Pleiotropy

One gene influencing multiple, seemingly unrelated phenotypes.

Epistasis

A gene at one locus alters the expression of a gene at a second locus.

Multifactorial

Trait influenced by multiple genes and environmental factors.

Pedigree

Family tree showing inheritance patterns across generations.

Autosomal inheritance

Genes on autosomes; usually shows a 50/50 distribution between sexes.

X-linked inheritance

Gene located on X chromosome; often more males affected, pattern differs from autosomal.

Carrier

Heterozygous individual (Aa) who does not show a recessive disorder but can pass it on.

Albinism

Recessive genetic disorder causing lack of pigment.

Achondroplasia

Dominant genetic disorder causing dwarfism; can be borne by affected individuals.

Self-fertilization

Fertilization within the same flower; can produce uniform traits but not always identical offspring.

Genotype

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