Genetics Post-Midterm Content

Transposable Element (Transposon)

A DNA sequence that can move from one location in the genome to another

Transposition

The movement of a transposable element from one genomic location to another

Autonomous Element

A transposable element that encodes the proteins required for its own movement

(eg: transposase)

Non-autonomous Element

A transposable element that cannot move on its own and requires proteins produced by an autonomous element

Ac (Activator)

An autonomous transposable element in maize that produces transposase and allows transposition

Ds (Dissociation)

A non-autonomous transposable element in maize that require Ac for movement

Transposase

An enzyme that recognizes transposable elements and catalyzes their movement within the genome

Insertion Sequence (IS) Element

The simples bacterial transposable element containing only a transposase gene flanked by inverted repeats

Inverted Repeat (IR)

Identical DNA sequences found in opposite orientations at the ends of a transposable element

Composite Transposon

A bacterial transposon consisting of two IS elements surrounding additional genes, often antibiotic resistance genes

Simple Transposon

A transposon contains transposition genes and other genes flanked by inverted repeats but lacking IS elements

Ploidy

The number of complete chromosome sets in a cell

Euploidy

A condition in which a cell contains complete chromosome sets

Aberrant Euplody

Having more of fewer complete chromosome sets than normal

Polyploid

An organism with three or more complete chromosome sets

Aneuploid

An organism that has gained or lost one or more chromosomes but not an entire chromosome set

Monoploid

An individual possessing only one chromosome set

Genetic Load

The collection of deleterious recessive alleles present in a poplulation or genome

Parthenogenesis

Development of an embryo from an unfertilized egg

Autopolyploid

A polyploid whose chromosomes all originate from the same species

Allopolyploid

A polyploid whose chromosome sets originate from different species

Homeologous Chromosomes

Chromsomes from different species that are partially homologous

Triploid (3n)

An organism containing three complete chromosome sets

Tetraploid (4n)

An organism containing four complete chromosome sets

Bivalent

A pair of homologous chromosomes aligned during meiosis

Univalent

A chromosomes that remains unpaired during meiosis

Trivalent

Three homologous chromosomes paired together during meiosis

Amphidiploid

A fertile allopolyploid formed after chromosome doubling restores homologous pairing

Colchicine

A chemical that blocks microtubule formation and can induce chromosome doubling

Nullisomy (2n-2)

Loss of both members of a homologous chromosome pair

Monosomy (2n-1)

Loss of a single chromosome

Trisomy (2n+1)

Presence of one extra chromosome

Tetrasomy (2n +2)

Presence of two extra copies of the same chromosome

Chromosome Rearrangement

A structural change in a chromosome caused by the breakage and rejoining of DNA

Nonallelic Homologous Recombination (NAHR)

Crossing over between similar DNA sequences located at different positions; also called unequal crossing over

Unequal Crossing Over

Recombination between misaligned homologous sequences resulting in deletions or duplications

Unbalanced Rearragement

A chromosomal rearrangement that removes a segment of DNA

Deletion

A chromosome rearrangement that removes a segment of DNA

Intragenic Deletion

A deletion occurring within a gene that often produces a null allele

Deletion Loop

A loop formed during meiosis when one homologous contains a deletions and the normal homologous has extra unpaired DNA

Pseudodomiance

Expression of a recessive allele because the dominant allele has been deleted

Duplication

A chromosome rearrangement that increases the copy number of a chromosomal region

Tandem Duplication

A duplicated segment located immediately adjacent to the original segment

Insertional Duplication

A duplicated segment inserted elsewhere in the genome

Gene Dosage

The number of copies of a gene present in a cell

Balanced Rearrangement

A chromosomal rearrangement in which no DNA is gained or lost

Inversion

A chromosome rearrangement in which the segment rotates 180 degrees and reinserts into the chromosome

Paracentric Inversion

An inversion that does not include the centromere

Pericentric Inversion

An inversion that includes the centromere

Reciprocal Translocation

An exchange of chromosome segments between two non-homologous chromosomes

Centromere

The chromosome region where spindle fibres attach during cell division

Telomere

A repetitive DNA sequence at the end of a chromosome that protects chromosome ends

Acentric Chromosome

A chromosome fragment lacking a centromere

Homologous Chromosomes

Chromosomes with the same genes arranged in the same order that pair during meiosis

Gene Dosage Effect

Changes in phenotype caused by altered copy number of genes