Heredity & Genetics – Core Vocabulary

A comprehensive set of vocabulary flashcards covering fundamental genetics terminology, Mendelian laws, patterns of inheritance, chromosomal anomalies, and cancer-related gene concepts.

Gene

A basic unit or sequence of genetic material that encodes a trait.

Locus

The specific physical location of a gene on a chromosome.

Allele

A variant form of a gene found at a given locus.

Wild type

The normal, most common form of an allele in a population.

Mutant allele

An allele whose DNA sequence is altered, producing an atypical phenotype.

Genotype

The set of alleles an individual carries (e.g., Aa, BB).

Phenotype

Observable characteristics produced by expression of the genotype.

Homologous chromosomes

A maternal-paternal pair containing the same genes in the same order.

Hemizygous

Having only one copy of a gene instead of two (e.g., genes on a male’s X chromosome).

Heterozygous

Genotype with two different alleles for a gene (e.g., Aa).

Homozygous

Genotype with identical alleles on both homologs.

Homozygous dominant

Genotype with two dominant alleles (e.g., BB).

Homozygous recessive

Genotype with two recessive alleles (e.g., bb).

Law of Segregation

Allele pairs separate during gamete formation so each gamete carries one allele per gene.

Law of Independent Assortment

Segregation of one pair of homologs does not influence segregation of another pair.

Law of Dominance

A dominant allele masks the phenotypic effect of a recessive allele.

Punnett square

A diagram that predicts all possible gamete combinations and offspring genotypes.

Test cross

Cross between an individual of unknown genotype and a homozygous recessive to reveal the unknown genotype.

Monohybrid cross

Genetic cross tracking a single gene.

Dihybrid cross

Genetic cross tracking two different genes simultaneously.

Epistasis

Interaction where one gene masks or modifies the phenotypic expression of another independently inherited gene.

Multiple alleles

More than two common allelic forms exist for a gene (e.g., ABO blood group).

Polygenic inheritance

Many genes collectively influence a single trait, producing continuous variation (e.g., height).

Pleiotropy

One gene affects multiple distinct phenotypic traits.

Incomplete dominance

Heterozygote shows an intermediate phenotype (alleles blend, e.g., red × white → pink).

Codominance

Both alleles in a heterozygote are fully and simultaneously expressed (e.g., AB blood type).

Sex-linked gene

Gene located on a sex chromosome (X or Y).

Sex-influenced gene

Gene whose expression differs between sexes despite identical genotypes (e.g., pattern baldness).

Linked genes

Genes located close together on a chromosome that tend to be inherited together.

Linkage map

Diagram showing relative gene positions based on recombination frequency.

Recombination frequency

Percentage of recombinant offspring; indicates distance between linked genes.

X-inactivation

Random silencing of one X chromosome in female mammals, producing a Barr body.

Barr body

Highly condensed, inactivated X chromosome in female somatic cells.

Aneuploidy

Abnormal chromosome number (extra or missing chromosomes).

Trisomy 21 (Down syndrome)

Condition caused by three copies of chromosome 21.

Nondisjunction

Failure of homologs or sister chromatids to separate during meiosis or mitosis, producing aneuploid gametes.

Penetrance

Proportion of individuals with a genotype who actually display the associated phenotype.

Expressivity

Degree or intensity of a phenotype expressed by individuals with the same genotype.

Autosomal dominant inheritance

One mutant allele on an autosome suffices to express the disorder; appears in every generation.

Autosomal recessive inheritance

Two mutant alleles on an autosome are required to express the disorder; can skip generations.

X-linked dominant inheritance

Single mutant allele on the X chromosome causes the trait in both sexes; affected fathers pass it to all daughters.

X-linked recessive inheritance

Trait requires two mutant X alleles in females but only one in males; affects males more frequently.

Y-linked inheritance

Traits determined by genes on the Y chromosome; transmitted father-to-son only.

Colchicine

Drug that blocks spindle formation, arresting mitosis; used in cancer therapy and karyotyping.

Proto-oncogene

Normal gene that promotes cell growth; mutation converts it to an oncogene.

Oncogene

Mutated proto-oncogene that drives uncontrolled cell proliferation and cancer.

Tumor suppressor gene

Gene encoding proteins that restrain cell division; loss-of-function mutations can lead to cancer.

Chromosomal aberration

Structural or numerical change in chromosomes, including inversions, deletions, translocations, and duplications.

Inversion

Chromosomal segment reinserted in reverse orientation.

Deletion

Loss of a chromosomal segment.

Translocation

Segment moved to a non-homologous chromosome; may be reciprocal or non-reciprocal.

Duplication

Repeating of a chromosomal segment on the same chromosome.