1. Human Genetics part 2

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

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

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

11. Monosomy X Abnormality shown in karyotype
Note this person only has 1 copy of the X chromosome.
This female has Turner’s syndrome.

12. Turner’s Syndrome
Usually, a woman has two X chromosomes. However, in women with Turner’s syndrome, one of these chromosomes is absent or abnormal.
With appropriate medical treatment and support, a girl or woman with Turner’s syndrome can lead a normal, healthy and productive life.
Treatment aims to correct any physical defects and help bring about puberty.

13. XXY Male (Extra X)

14. Klinefelter’s Syndrome
A male with Klinefelter syndrome has an additional X chromosome, which causes infertility, low testosterone and other characteristics such as development of breast tissue.
The chromosomes are present in every cell of the body and the extra X chromosome cannot be removed.
Treatment includes lifelong testosterone therapy and cosmetic surgery to remove enlarged breast tissue. Options for men with Klinefelter syndrome to have their own children are becoming more widely available.

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.

19. Revisit Meiosis?
Crash Course Biology (be sure to pause the video and rewind if needed)

20. Nondisjunction

21. How can siblings look alike but not exactly the same if they come from the same parents?

22. Crossing over
The chromosomes during prophase I undergo crossing over, where parts of the homologues randomly switch places.

23. Importance of crossing over
The gene combinations that a person gets from his or her parents will be different, to varying degrees, than the combination a sibling may get.

24. More sibling similarities

25. What other chromosomal disorders can arise?
Deletion
Inversion
Translocation
Duplication

26. Chromosomal mutations
Deletion
Duplication
Inversion
Translocation

27. Problems with chromosomes
Duplication: copied parts of chromosome A B C D A B C D

28. Problems with chromosomes
Deletion: missing parts of chromosome A B C D A D

29. Problems with chromosomes
Inversion: parts of chromosome tched A B C D A C B D