VNTRs and Electrophoresis – Vocabulary Flashcards

Vocabulary flashcards covering VNTRs, their biology, and forensic testing steps.

VNTR (Variable Number Tandem Repeat)

A size polymorphism where short DNA repeat units (6–100 bp) are repeated in tandem; a forensic marker with thousands of copies at a locus.

Minisatellites

Another name for VNTRs; short repeated DNA sequences repeated in tandem in the genome.

Polymorphism

Genetic variation between individuals, including sequence changes (base substitutions) and length changes (insertions/deletions) across gene and non-gene regions.

Sequence change

A base substitution that alters the DNA sequence at a locus.

Length change

Insertion or deletion of DNA bases that changes the length of a DNA fragment.

Junk DNA

Noncoding DNA; highly repetitive regions that comprise much of the genome and are useful in forensics.

Repetitive DNA

DNA sequences that occur in many copies; includes VNTRs and other repeats.

Protein coding DNA

DNA sequences that contain instructions to make proteins.

Pseudogenes

Nonfunctional gene copies derived from functional genes.

Unique non-coding DNA

Noncoding DNA sequences that occur in a unique location in the genome.

Telomeres

Chromosome ends that protect genetic material; composed of repetitive TTAGGG sequences.

TTAGGG

The six-base telomere repeat sequence found in human telomeres.

Repeat Unit

The number of bases that make up a single repeat in a VNTR (e.g., 6 bp).

Repeat Sequence

The exact sequence of bases in the VNTR repeat unit.

Copy Number

Number of consecutive repeat units present at a VNTR locus on a chromosome.

Allele

A particular copy number variant at a VNTR locus; each person has two alleles for each locus.

Locus

A specific location on a chromosome where a VNTR is found.

VNTR Alleles

Different possible copy-number variants at a VNTR locus; thousands are possible.

Inheritance of VNTRs

VNTR alleles are inherited from parents; copy numbers can differ between homologous chromosomes.

Single-locus VNTR

VNTR analysis targeting one locus; typically yields two bands and is quicker to run.

Multilocus VNTR probe

A DNA probe that detects multiple VNTR loci on a single membrane (requires more DNA and time).

Restriction Enzyme

Bacterial enzymes that cut DNA at specific recognition sequences, used to digest DNA in VNTR analysis.

Restriction site

The specific DNA sequence recognized and cut by a restriction enzyme.

Recognition sequence

The short DNA sequence (usually 4–8 bp) recognized by a restriction enzyme.

Blunt cut

Restriction enzyme cut that occurs straight through the recognition sequence, leaving blunt ends.

Sticky ends

Restriction enzyme cut offset from the center, leaving overhanging single-stranded ends.

Palindromic sequence

A DNA sequence that reads the same 5' to 3' on opposite strands; common in restriction sites.

DNA Fragment

Pieces produced by restriction digestion; some contain VNTRs and vary in length.

DNA Ladder

A set of DNA fragments of known sizes used as a ruler to estimate sample fragment sizes.

Gel Electrophoresis

Technique that separates DNA by size using an electric field; smaller pieces move faster.

Lanes

Individual sample tracks in an electrophoresis gel; samples should be run on the same gel for comparison.

Southern Blotting

Transfer of DNA fragments from a gel to a nitrocellulose membrane for probing.

Probing

Hybridization of labelled probes to complementary VNTR sequences on the membrane to visualize VNTRs.

Probes

Labeled DNA fragments that are complementary to the target VNTR sequence.

Multilocus VNTR Probe

A probe that targets multiple VNTR loci on one membrane to generate a multilocus profile.

Alec Jeffreys

Pioneer of DNA fingerprinting (1985) who demonstrated VNTR patterns that are unique to individuals.

DNA Fingerprint

A VNTR pattern unique to an individual, used for identification and paternity; inherited from parents.

Paternity Exclusion

Conclusion that a tested man cannot be the father because VNTR alleles are incompatible.

Paternity Inclusion

Conclusion that a tested man could be the father because VNTR alleles are compatible.

D1S7

A commonly used single-locus VNTR marker with many known alleles used in forensic typing.

Probability of a random match

The chance that two unrelated individuals share the same VNTR allele profile; decreases as more markers are used.

Single-locus VNTRs (examples)

Markers such as D1S7, D2S44, D4S139, D10S28, D14S13, D17S79; each has multiple alleles.