A picture of a person’s chromosomes. Karyotypes A picture of a person’s chromosomes.

Karyotype A karyotype is an organized profile of an individuals chromosomes. The Chromosomes are identified, numbered and arranged from largest to smallest. Chromosomes can then be examined to identify genetic disorders.

Prenatal Genetic Testing How are fetal cells obtained? 1. Amniocentesis

AMNIOCENTESIS A sample of amniotic fluid which contains fetal cells, is taken after the 14th week of pregnancy

2. CHORIONIC VILLUS SAMPLING A sample of cells from the chorion (part of the placenta) is taken after the 9th Week of pregnancy

CHORIONIC VILLUS SAMPLING

HUMAN CHROMOSOMES ALL MIXED UP

NORMAL HUMAN KARYOTYPE

WHAT’S DIFFERENT? Examine the chromosomes. How does this karyotype differ from a normal karyotype?

DOWN’S SYNDROME KARYOTYPE Three copies of chromosome #21

WHAT’S DIFFERENT?

TURNER’S SYNDROME Missing a sex chromosome.

WHAT’S DIFFERENT?

XXY SYNDROME An extra sex chromosome.

WHAT’S DIFFERENT?

XYY SYNDROME

ONE OF CHROMOSOME 7 HAS PART MISSING (DELETION)

Monosomy and Trisomy Monosomy – missing a chromosome Trisomy – an extra chromosome

NON-DISJUNCTION The failure of chromosomes or tetrads to separate properly during anaphase is called non-disjunction. This results in the addition or deletion of a chromosome in a gamete.

If it happens in meiosis I, all the resulting cells will be affected If it happens in meiosis I, all the resulting cells will be affected. If it happens in meiosis II, only half will be affected.

NON-DISJUNCTION If a gamete with an extra chromosome is fertilized by a normal gamete, the zygote will have an extra chromosome, called trisomy. If a gamete missing a chromosome is fertilized by a normal gamete, the zygote will have only one copy of a chromosome, called monosomy.

How does this happen? NONDISJUNCTION ANIMATION at MEIOSIS I http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm

NONDISJUNCTION MEIOSIS II http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20II.htm

WHAT’S DIFFERENT?

Changes in chromosome structure animation http://highered.mcgraw-hill.com/sites/0035456775/student_view0/chapter10/changes_in_chromosome_structure.html