Cytogenetics Study of Chromosomes

Chromosomes 23 pairs Numbered and arranged by size and position of centromere

Chromosomes Can be displayed on a karyotype This shows extra, missing, or fragmented chromosomes

Chromosomes Coiled DNA, with some RNA and histone proteins DNA strand coils around histones, which look like beads Histones can alter the activity of the DNA (turn genes on or off)

Obtaining Cells Obtain cells by 4 methods: Amniocentesis Chorionic villus sampling Fetal Cell sorting Maternal blood screening

Chromosomes Staining techniques point out bands FISH allows more bands to be seen Can fish for a particular piece

Chromosomes Symbols show aberrations 46, XY normal male 46,XX normal female 45,XO Turner syndrome 47, XX 21 Trisomy 21

Wrong Number Polyploidy: an entire set is affected; one or more extra sets Could be triploid Aneuploidy: one extra or missing chromosome As in Down Syndrome (Trisomy 21) Caused by nondisjunction or translocation In translocation, chromosomes break and swap ends Triploidy

Changes in chromosome structure Major categories include duplication, inversion, translocation, deletion

Duplication Certain gene sequences are repeated. May be just once, may be thousands of times The more copies, the more severe the disorder May get worse with each generation

Inversion No genes are lost, but order is changed A piece becomes oriented in the reverse direction Detaches, flips around, and reattaches.

Translocation Can have no affect if all parts are there Causes problems when a sperm or egg gets the normal chromosome and the extra attached to another

Deletion Loses a segment of the chromosome Most serious; often lethal Missing 3 is less serious than missing one. Why? Could cause a frameshift

A point mutation Only involves a single base change Not a total chromosome problem Can still cause a problem. Why?