Genetic Terms Glossary — DNAtest.cz | DNA, STR, PCR and more

A

Allele

One of the alternative forms of a gene at a given chromosomal location (locus). Each person has two alleles for each gene — one from the father and one from the mother.

Amplification

The process of multiplying specific DNA segments many times using PCR. Allows analysis from even trace amounts of biological material.

C

Chromosome

A structure in the cell nucleus containing DNA in the form of a double helix. The human genome consists of 46 chromosomes (23 pairs). X and Y chromosomes determine an individual's sex.

D

DNA (deoxyribonucleic acid)

The molecule that carries the genetic information of all living organisms. It consists of four nucleotide bases — adenine (A), cytosine (C), guanine (G) and thymine (T) — arranged in a double helix.

DNA profile

A unique set of genetic markers (STR loci) characteristic of a specific individual. Used in forensic genetics, personal identification and paternity testing.

E

Electrophoresis

An analytical method that separates DNA fragments by size using an electric field. Results are visualised as bands on a gel or via capillary electrophoresis in modern instruments.

G

Gene

A segment of DNA carrying instructions for producing a specific protein or RNA. The human genome contains approximately 20,000–25,000 genes.

Genotype

The complete genetic makeup of an individual — the sum of all alleles in their genome. The genotype is fixed from fertilisation and does not change throughout life.

H

Haplotype

A set of genetic variants (SNPs or STRs) that are inherited together. Y-chromosome and mtDNA haplotypes are used in genealogical genetics.

Haplogroup

A group of individuals sharing a common ancestor identified through characteristic SNP mutations in the Y chromosome or mitochondrial DNA. E.g. haplogroup R1a = predominates among Slavs.

L

Locus

The precise position of a gene or genetic marker on a chromosome. Paternity tests analyse 16–26 STR loci.

M

Marker (genetic)

An identifiable DNA sequence at a specific genomic location. STR markers — short tandem repeats with high variability between individuals — are used in paternity testing.

Microsatellite (STR)

A Short Tandem Repeat — a sequence of 2–6 nucleotides repeated in a row. Each person has a different number of repeats, making microsatellites ideal markers for personal identification.

Mitochondrial DNA (mtDNA)

DNA contained in mitochondria — the cell organelles that produce energy. Inherited exclusively through the maternal line. Used for tracing maternal genealogical origins.

Mutation

A change in the DNA sequence. Can be beneficial, harmful or neutral. In genealogy, accumulated mutations allow dating of haplogroup ages and population migrations.

N

Nucleotide

The basic building unit of DNA and RNA. Consists of a sugar component (deoxyribose), a phosphate group and a nitrogenous base (A, C, G or T in DNA).

P

PCR (Polymerase Chain Reaction)

A molecular biology method for amplifying specific DNA segments. Enables the creation of millions of copies of a target DNA segment from a minimal sample. The key technique in all DNA tests.

Polymorphism

The existence of two or more forms (alleles) at a given genomic location in a population. SNP (Single Nucleotide Polymorphism) is the most common type of genetic polymorphism.

Likelihood Ratio (LR)

A statistical indicator in paternity and relationship tests. Expresses how many times more likely it is that the tested person is a biological relative compared to a random person from the population.

S

DNA Sequencing

A method for determining the precise order of nucleotide bases in a DNA sequence. Modern next-generation sequencing (NGS) allows reading the entire human genome. Used in genealogical testing and mtDNA analysis.

SNP (Single Nucleotide Polymorphism)

A variation in a single nucleotide at a specific genomic position. SNPs are the most common type of genetic variation — millions exist in the human genome. Used in genealogy, nutritional genetics and medicine.

STR locus

Short Tandem Repeat — see Microsatellite. The standard type of marker analysed in forensic and identification genetics. The international CODIS standard includes 20 core STR loci.

X / Y / Z

X chromosome

A sex chromosome. Females have two copies (XX), males one (XY). The X chromosome carries hundreds of genes unrelated to sex.

Y chromosome

The male sex chromosome passed exclusively from father to son. Contains genes responsible for male development and is the key tool for tracing the paternal genealogical line.

Zygote

The cell formed by the fusion of egg and sperm during fertilisation. Contains a complete set of 46 chromosomes — 23 from the mother and 23 from the father. The zygote is the starting point for a new organism's development.