Lecture 7

Gene Structure and Transposable Elements

Gene structure

Gene families

Repetitive DNA including transposons

Organelle genomes

Reading: Chapter 10

Molecular Biology syllabus web site

Gene Structure

Gene Families-tissue-specific and temporal-specific expression

-diverging activities or localization

DNA Classes

Reassociation experiments reveal three major fractions of eukaryotic DNA

• Single copy DNA (50-60%)

• Moderately-repeated/ intermediate-repeat DNA (25-40%); includes mobile DNA elements

• Simple-sequence DNA (10-15%)

Human metaphase chromosomes: in situ hybridization with fluorescent-labelled “simple

sequence” DNA probe

Human DNA fingerprints

DNA probed with 3 different microsatellite DNA probes a,b,c show characteristic patterns of individuals.

Probe ‘b’

Mutable phenotypes caused by transposable elements

nonmutable

mutable

Transposable Elements

Transposable element excision results in target site duplication or other DNA sequence changes

Chromatin Structure

Nucleosomes

DNA

DNA

Cultured undifferentiated MSB cellsDifferentiated red blood cells at 14 days

Chromatin structure changes during differentiation of cells