1. Abnormal Meiosis

2. What each of the human chromosomes look like

3. Karyotype: A photomicrograph of chromosomes arranged according to a standard classification

4. In other words… • Chromosomes are digitally arranged so that they are matched with their homologue or “partner” chromosome. • Homologue chromosomes are the same size, shape, and carry the same genes, and one is inherited from each parent. • They are numbered according to size.

5. Sex determination with karyotype • This karyotype has 23 exact pairs, which means the person is female. • Note that #23 chromosomes are both X.

6. Normal human male • Note that #23 chromosomes are X and Y.

7. Is this person female or male?

8. Is this person female or male?

9. Trisomy 21 • Abnormality shown in karyotype • Note that there are three copies of #21 chromosome. • This person has Down Syndrome.

10. Photos of Down Syndrome patients from the National Down Syndrome Society

11. Correlation between mother’s age and Trisomy 21 incidence

12. Monosomy X • Abnormality shown in karyotype • Note this person only has 1 copy of the X chromosome. • This female has Turner’s syndrome. • Occurs 1 in 2500 females

13. XXY Male (Extra X) • Affected individuals have at least two X chromosomes and at least one Y chromosome. • The most common sex chromosome disorder • This male has Klinefelter’s syndrome. • Occurs 1 in 500 males

15. How are DNA samples obtained for karyotypes?

16. Amniocentesis: obtaining amniotic fluid which has cells from the fetus

17. Chorionic villi sampling: removing cells from the chorion with fetal tissue

18. If there are chromosomal number abnormalities, how do they form? • Meiosis: the process of creating sperm or egg from a diploid cell • If there is a mistake when chromosomes are separating, then the resulting sperm or egg will have too many or too few chromosomes.