Karyotypes & Chromosomal Disorders

1. Karyotypes&Chromosomal Disorders Journal Notes

2. Human Karyotype

3. Karyotypes • photograph of one’s chromosomes, grouped in pairs of homologous chromosomes by size • Humans have 1 pair of sex chromosomes (XX or XY) and 22 pairs of autosomes (chromosomes that are not sex chromosomes).

4. Chromosome Abnormalities • All abnormalities result from an error during meiosis, called “nondisjunction” non – dis – junction • The problem arises when during meiosis there is a failure of homologous chromosomes to separate.

5. Non-disjunction of chromosomes

6. Nondisjunction of chromosomes • If non-disjunction occurs, one gamete gets both chromosomes, the other gamete gets nothing.

7. Analyzing Karyotypes: 1. Are there 46 chromosomes? 2. Are there 2 identical chromosomes in each pair of autosomes and 2 sex chromosomes? 3. Are there any rearrangements between chromosomes or large, obvious deletions?

8. Individual DNA strands or genes or the DNA sequence The number of genes in a chromosome The presence of gene mutations Karyotypes DO NOT show:

9. 6 Chromosome Disorders caused by Nondisjunction • Down syndrome (trisomy 21) • Edwards syndrome (trisomy 18) • Klinefelters syndrome (trisomy XXY) • XYY syndrome (trisomy XYY) • XXX syndrome (trisomy X) • Turners syndrome (monosomy XO) **Nearly all other nondisjunctions lead to death of embryo or child before adulthood!

10. Chromosome Abnormalities • Down Syndrome – Extra copy of chromosome 21. Also called “Trisomy 21” • Have 47 chromosomes. • One of only a few trisomy disorders in which the child has high probability of living to adulthood • Short stature • Mental retardation • Reduced life span • Characteristic features

11. Down Syndrome Lauren Potter from “Glee”

12. Klinefelter Syndrome • XXY – Male • trisomy of the sex chromosomes • 47 Chromosomes • Sterile • Low testosterone • Taller than average • Often don’t know they have it unless tested.

13. Klinefelter Syndrome XXY

14. XYY Syndrome • Males with extra Y. • 47 chromosomes • Taller than average • Normal development – never know they have it unless tested. • May have sterility problems

15. XXX Syndrome • Females with extra X • 47 chromosomes • Taller than average • Often develop normally – never know they have it unless tested. • May have sterility problems

16. Turner Syndrome • XO females. • Missing 2nd sex chromosome. • This is the only monosomy in which the embryo survives. If any other chromosomes are missing then embryo/fetus does not survive. • 45 chromosomes • Sterile • Shorter than average • various other characteristic symptoms

17. Turner Syndrome - XO