Heredity and Genetics – Core Vocabulary

Vocabulary flashcards summarizing essential terms and definitions drawn from the Heredity and Genetics pre-assessment content.

Allele

One of two or more alternative forms of a gene found at the same locus on homologous chromosomes.

Genotype

The genetic makeup of an organism; the combination of alleles it possesses for a given trait.

Phenotype

The observable traits or characteristics of an organism that result from the interaction of its genotype with the environment.

Homozygous

Having two identical alleles for a particular gene (e.g., AA or aa).

Heterozygous

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

Dominant Allele

An allele that masks the expression of another allele and determines the phenotype when present.

Recessive Allele

An allele whose expression is masked by a dominant allele; expressed only in the homozygous condition.

Incomplete Dominance

Inheritance pattern in which the heterozygote displays an intermediate phenotype (e.g., red × white ➜ pink flowers).

Codominance

Inheritance pattern in which both alleles in a heterozygote are fully expressed (e.g., red and white stripes).

Polygenic Inheritance

A trait controlled by two or more genes, often showing a continuous range of phenotypes (e.g., skin color, height).

Additive Model

Polygenic model in which each allele adds a specific quantitative amount to a trait (e.g., centimeters to height).

Punnett Square

A diagram used to predict genotypic and phenotypic ratios resulting from a genetic cross.

Phenotypic Ratio

The relative proportions of observable traits among the offspring of a genetic cross.

Dihybrid Cross

A genetic cross tracking two different traits, often producing a 9:3:3:1 phenotypic ratio when the genes assort independently.

Gene

A segment of DNA that codes for a specific protein or functional RNA.

Homologous Chromosomes

Pairs of chromosomes, one from each parent, that carry genes for the same traits at the same loci.

Sister Chromatids

Identical copies of a chromosome held together by a centromere after DNA replication.

Meiosis

A two-stage cell division that reduces the chromosome number by half, producing four haploid gametes.

Meiosis I

The first meiotic division in which homologous chromosomes separate, reducing the chromosome number.

Meiosis II

The second meiotic division in which sister chromatids separate, similar to mitosis.

Metaphase I

Stage of meiosis where homologous chromosome pairs align at the cell’s equator.

Anaphase II

Stage of meiosis where sister chromatids are pulled apart toward opposite poles.

Independent Assortment

Random orientation of homologous chromosome pairs during Metaphase I, leading to genetic variation.

Crossing Over

Exchange of genetic material between nonsister chromatids of homologous chromosomes during Prophase I.

Haploid

Having one complete set of chromosomes (n); characteristic of gametes.

Diploid

Having two complete sets of chromosomes (2n); characteristic of somatic cells.

Nondisjunction

Failure of chromosomes or chromatids to separate properly during meiosis, leading to aneuploidy.

Aneuploidy

Abnormal number of chromosomes, such as trisomy (2n+1) or monosomy (2n−1).

Polyploidy

Condition in which a cell has more than two complete sets of chromosomes (e.g., 3n, 4n, 5n).

Trisomy

Presence of an extra chromosome (2n+1), resulting in 47 chromosomes in humans.

Tetraploidy

Having four complete sets of chromosomes (4n).

Monosomy

Missing one chromosome from a pair (2n−1).

X-Linked Recessive

Mode of inheritance where the recessive allele on the X chromosome causes a trait that predominantly affects males.

X-Linked Dominant

Mode of inheritance where a dominant allele on the X chromosome expresses the trait in both sexes but is often lethal in males if severe.

Autosomal Dominant

Trait controlled by a dominant allele located on a non-sex chromosome; appears in every generation.

Autosomal Recessive

Trait controlled by a recessive allele on an autosome; expressed only when homozygous recessive.

Missense Mutation

Point mutation resulting in a codon that codes for a different amino acid (e.g., CUG ➜ GUG).

Nonsense Mutation

Point mutation that converts a codon encoding an amino acid into a stop codon, truncating the protein.

Frameshift Mutation

Insertion or deletion of nucleotides not in multiples of three, altering the reading frame of a gene.

Insertion Mutation

Addition of one or more nucleotide pairs into a DNA sequence.

Deletion Mutation

Loss of one or more nucleotide pairs from a DNA sequence.

Point Mutation

Change in a single nucleotide pair in DNA.

Base Analog

Chemical that mimics normal DNA bases and can be incorporated during replication, causing mutations.

Radiation

Physical mutagen (e.g., X-rays, UV light) that can cause DNA breaks or thymine dimers.

Reactive Oxygen Species

Highly reactive molecules that can chemically modify DNA bases, leading to mutations.

DNA Sequencing

Technique used to determine the precise order of nucleotides in a DNA molecule.

Recombinant DNA

DNA molecules formed by lab methods to bring together genetic material from multiple sources.

Polymerase Chain Reaction (PCR)

Method to amplify specific DNA sequences exponentially using repeated cycles of denaturation, annealing, and extension.

Plasmid Vector

Circular DNA molecule used to carry foreign DNA into a host cell in genetic engineering.

DNA Microarray

Technology that uses thousands of short DNA probes on a chip to measure gene expression levels simultaneously.

DNA Profiling

Technique that compares DNA samples to establish identity or genetic relationships; used in forensics and ancestry testing.

Stem Cell

Undifferentiated cell capable of self-renewal and differentiating into specialized cell types.

Cloning

Producing genetically identical organisms or cells from a single ancestor via somatic cell nuclear transfer or other methods.

Apoptosis

Programmed cell death that removes unneeded or damaged cells without causing inflammation.

Senescence

Permanent cell cycle arrest where a cell remains metabolically active but no longer divides.

Cancer

Disease characterized by uncontrolled cell division and the ability to invade other tissues.

Proofreading (DNA Polymerase)

Enzymatic correction of mismatched bases during DNA replication to maintain fidelity.

Natural Selection

Process by which individuals with advantageous traits are more likely to survive and reproduce, changing allele frequencies.

Genetic Drift

Random changes in allele frequencies in a small population due to chance events.

Founder Effect

Genetic drift that occurs when a new population is established by a small number of individuals, reducing genetic variation.

Speciation

Formation of new species when populations become reproductively isolated and diverge genetically.

Hardy-Weinberg Equilibrium

Principle stating that allele and genotype frequencies remain constant from generation to generation in an ideal population.

Allele Frequency

Proportion of a specific allele among all alleles for a given gene in a population.