KARYOTYPING AND NON-DISJUNCTION

1. KARYOTYPING AND NON-DISJUNCTION Downloaded from authorstream.com

2. What is karyotyping? • A method of identification of chromosomes • Pictures of chromosomes are taken as the cell undergoes mitosis • The image is enlarged • Individual chromosomes are cut up • Chromosomes are matched up based on: • Size (largest to smallest) • Centromere position

3. A mess of chromosomes…

4. After karyotyping… a normal male 46, XY

5. After karyotyping… a normal female 46, XX

6. Non-disjunction • Non-disjunction is a failure of chromosomes to properly separate during either Stage 1 or Stage 2 of meiosis • What causes the chromosomes NOT to separate?? • Upon fertilization the zygote may have one too many chromosomes ( trisomy) or one too few chromosomes (monosomy) • All but one monosomy case results in death

7. Non-disjunction • Non-disjunction occurs quite often among humans • Impact is so severe to the zygote that miscarriage occurs very early in the pregnancy • If the baby survives, it develops a set of traits that we call a syndrome

8. Down’s Syndrome • Most commonly known trisomy 21 • 1:700 births; 1 in 6 die within 1st year • Average age is 16.2 years • Common facial feature • Short stature • Stubby fingers and toes • Large tongue – makes speech difficult

9. Down’s syndrome 47, XY, +21

10. Down’s Syndrome • One of the most common causes of mental disability (IQ is in the 25-75 range) • Prone to heart defects, respiratory problems and leukemia

11. Down’s Syndrome • Odds of having a Down’s child increases with the age of the mother • 1 in 1500 if mom is in early 20’s • 1 in 70 if mom is over 35 • 1 in 25 if mom is over 45

12. Patau Syndrome • 1:15,000 births as most fetuses die before term • Of those that survive, 5% live to age 3; 45% die within the first month • Serious eye, brain, and circulatory defects

13. Patau’s Syndrome

14. Edward’s Syndrome • Only 10% survive past one year • All die early in infancy • Many complications

15. These are the only known trisonomy genetic disorders that result in offspring surviving for a short period of time

16. Non-disjunction of the sex chromosomes • These can be fatal • Most do survive just fine

17. Klinefelter’s Syndrome • XXY • Affects 1:500 males • Tall, sterile males • Normal intelligence

18. Jacob’s Syndrome (super male) • XYY • Somewhat taller than average • Slightly below normal intelligence • 1:1000 males • Extra testosterone • Once thought to be more likely to become criminals

19. XXX (super female?) • 1:1000 live births • Normal intelligence • Fertile • No physical problems • There are some women who are XXXX and XXXXX – each increasing X results in lesser intelligence and fertility

20. Monosomy – Turner’s Syndrome (XO) • 1:2700 births • Live normal lives but do not mature sexually at puberty • Sterile • Short stature • Short broad neck • Broad chest

21. Other chromosomal issues • Deletion – a segment of the chromosome is missing • Example: Cri-du-chat (1:1,000,000) • Improperly developed larynx • Severely mentally handicapped

22. Other chromosomal issues • Duplication • Ex. Fragile X 1:1500 males, 2500 females Most common form of mentally handicapped offspring