Lecture 14 Transposon insertions and Chromosome abnormalities

transposable elements

mobile genetic elements found in the genomes of prokaryotes, archaea and eukaryotes (selfish’ genetic elements)

transposition

sequences of DNA that can jump around within the genome of a single cell

transposase

enzyme which is necessary for movement to a new location on the chromosome

cut and paste

move from one site to another in the genome

copy and paste

leads to duplication of the transposon
at a new site

DNA transposable elements

encode a transposase enzyme that allows them to jump (prokaryotes and eukaryotes)

retrotransposons

transpose through an RNA intermediate (like a retrovirus) (eukaryotes)

deletion

part of a chromosome is missing

deletion

occurs when breaks are induced in chromosomes by viruses, chemicals, radiation, transposable elements and errors in recombination

duplication

part of a chromosome is duplicated

inversion

part of a chromosome is broken and reinserted in the opposite orientation

pericentric inversion

contains the centromere

paracentric inversion

does not contain the centromere

homozygous inversion & translocation

chromosome pairing during meiosis is OK

heterozygous inversion

can seriously screw up recombination between homologous chromosomes leading to gametes with defective chromosomes (embryo lethality)

translocation

part of a chromosome is moved to a new region

intrachromosomal translocation

a region moves elsewhere on the same chromosome

interchromosomal translocation

a region moves to a new chromosome

reciprocal translocation

two chromosomes swap pieces

euploid

having the correct chromosome number

polyploid

having an incorrect number of chromosomes sets

human diploid

2N 46 chromosomes (2 sets)

triploid

3N 69 chromosomes (3 sets)

tetraploid

4N 92 chromosomes (4 sets)

aneuploid

having an incorrect number of chromosomes

trisomic

a diploid genome with three copies of one chromosome 47 chromosomes (2N +1)

monosomic

a diploid genome with one copy of one chromosome 45 chromosomes (2N – 1)

nondisjunction

when homologous chromosomes or sister chromosomes do not separate during meiosis

generates gametes with an incorrect set of chromosomes

Barr body

inactive X chromosome