1. ABNORMAL MEIOSIS
Nondisjunction occurs when two homologous chromosomes fail to separate during meiosis or mitosis.
Daughter cell forms with too many or too few chromosomes

2. More serious effects if occurs during production of gametes
Nondisjunction occurs during anaphase I or anaphase II

3. ABNORMAL MEIOSIS Nondisjunction in humans produces:
Gametes with 22 and 24 chromosomes.
If the gamete with 24 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 47 chromosomes is produced.
The zygote will have three chromosomes rather than a pair.
This condition is referred to as trisomy

4. Nondisjunction results in gametes with too many or too few chromosomes.
Nondisjunction may take place during anaphase I (A) or anaphase II (B).

6. ABNORMAL MEIOSIS
If the gamete with 22 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 45 chromosomes is produced.
The zygote will have one chromosome rather than a pair
This condition is referred to as monosomy.
Once the cells of trisomic or monosomic zygotes begin to divide, each cell of body will be one plus or one minus a chromosome.

7. NONDISJUNCTION DISORDERS
Male & Female
Down Syndrome
Patau
XYY
Gender Specific
Turner Syndrome (female) X0
Triplo-X Syndrome (female)
XXX or XXXX
Klinefelter Syndrome (male)
XXY or XXXY
Jacob’s Syndrome (male)

8. Down Syndrome Trisomy 21 Physical signs: Symptoms: Flat face
Upward slant eyes
Abnormal ears
Thick tongue
Symptoms:
40 % congenital heart defects
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9. DOWN SYNDROME

10. Patau Syndrome Trisomy 13 Physical Signs: Symptoms: Very small eyes
Extra digits
Cleft lip
Cleft palate
Symptoms:
Heart defects
Brain/spinal cord abnormalities
5-10% survive to 1st birthday

11. Edward Syndrome Trisomy 18 Physical Signs: Symptoms: Small head & jaw
Clenched hands, crossed legs
Symptoms:
Congenital heart disease
50% do not survive beyond 7 days

12. Turner Syndrome Absence of all or part of the second X chromosome
Symptoms:
Small <4’9’’
Extra skin folds at neck
Failure to develop secondary sex characteristics
Health Conditions:
Infertile
Heart abnormalities

13. TURNER SYNDROME

14. Triple X Syndrome Trisomy X Symptoms: Health Effects
Taller than average
Few unusual symptoms
Health Effects
Learning disabilities
Delayed motor skills

15. Klinefelter Syndrome XXY Symptoms: Health Effects: Taller, leaner
Less body & facial hair
Health Effects:
90-95% infertile

16. Jacob’s Syndrome XYY Symptoms: Learning disabilities
Delayed motor skills
Motor tics (tremors)

17. JACOBS SYNDROME

18. NONDISJUNCTION DISORDER STATS
The chances of nondisjunction disorder increases with age
Chances of having a child with Down’s Syndrome
Conceiving between 20 and 24 years, 1 in 1490
Conceiving at age 40, 1 in 106
Conceiving at age 49, 1 in 11

19. KARYOTYPES A chart of chromosomes.
Obtained by mixing a small sample of tissue with a chemical that stimulates mitotic division.
Division is stopped during metaphase.
Chromosomes are stained
A picture is taken and chromosomes are paired up with their homologue.
Homologue chromosomes are similar in size, length, centromere location and banding pattern.
They are organized in decreasing size with the sex chromosome placed at the end.

21. Karyotype Info
The karyotype of a normal human female contains 23 pairs of homologous chromosomes:
22 pairs of autosomes
1 pair of X chromosomes
The karyotype of a normal human male contains:
The same 22 pairs of autosomes
one X chromosome
one Y chromosome

22. NORMAL MALE

23. Practise
Answer questions 1-6 on Pg. 586