Genetics Glossary

One of two or more variant forms of a gene that occupy the same locus on homologous chromosomes and can produce different phenotypic effects.

Any chromosome that is not a sex chromosome. Humans have 22 pairs of autosomes and one pair of sex chromosomes (XX or XY).

An individual who is heterozygous for a recessive allele associated with a genetic disorder, showing no symptoms but capable of passing the allele to offspring.

A sequence of three consecutive nucleotides in mRNA that specifies a particular amino acid or signals the termination of translation during protein synthesis.

The reciprocal exchange of genetic material between homologous chromosomes during prophase I of meiosis, resulting in recombinant chromosomes with new allele combinations.

A cell or organism containing two complete sets of chromosomes, one inherited from each parent, designated as 2n. In humans, the diploid number is 46.

The molecular process by which a double-stranded DNA molecule is copied to produce two identical daughter molecules, each containing one original and one newly synthesized strand (semiconservative replication).

Describes an allele that expresses its phenotypic effect in both the homozygous and heterozygous states, masking the expression of the recessive allele.

The complete set of chemical modifications to DNA and histone proteins in a cell that regulate gene expression without altering the DNA sequence itself.

The process by which information encoded in a gene is used to synthesize a functional product, typically through transcription of DNA into mRNA followed by translation into protein.

The set of rules by which the nucleotide sequence of mRNA is translated into the amino acid sequence of a protein, using three-letter codons that specify each of the 20 amino acids and three stop signals.

The complete set of genetic material present in an organism, including all of its genes as well as non-coding DNA sequences.

The genetic constitution of an organism at one or more loci, represented by the specific alleles present on its chromosomes.

A cell or organism containing a single set of unpaired chromosomes, designated as n. In humans, gametes (sperm and egg) are haploid with 23 chromosomes.

A statistical measure estimating the proportion of phenotypic variation in a population that is attributable to genetic differences among individuals, ranging from 0 to 1.

Having two different alleles at a particular genetic locus on homologous chromosomes.

Having two identical alleles at a particular genetic locus on homologous chromosomes, either both dominant or both recessive.

The specific physical position of a gene or DNA sequence on a chromosome. Each gene has a defined locus, and alleles of the same gene occupy the same locus on homologous chromosomes.

A permanent change in the nucleotide sequence of an organism's DNA, which may be spontaneous or induced and can range from single base changes to large chromosomal rearrangements.

A diagram showing the inheritance pattern of a particular trait across multiple generations of a family, used to determine whether a trait is dominant, recessive, autosomal, or sex-linked.

The observable characteristics of an organism, including its morphology, physiology, biochemistry, and behavior, resulting from the interaction of genotype and environment.

Describes an allele whose phenotypic effect is masked in the heterozygous state and is only expressed when the individual is homozygous for that allele.

A trait determined by a gene located on a sex chromosome, most commonly the X chromosome. X-linked recessive traits appear more frequently in males because they carry only one X chromosome.

The process by which the information in a DNA strand is copied into a complementary strand of messenger RNA by the enzyme RNA polymerase.

The process by which the nucleotide sequence of messenger RNA is decoded by ribosomes to assemble a specific chain of amino acids, producing a polypeptide or protein.