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

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 47 Chromosomes Sterile
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. 45 chromosomes
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