1. 17.4 Abnormal Meiosis

2. Polyploidy
This occurs when an organism has more than 2 set of chromosomes
Is not a desirable occurrence in humans but is common in plants (ex. Wheat and potatoes)
3n or even 4n are possibilities

3. Karyotype
karyotype is the display that is formed when the chromosomes are arranged in pairs according to size with the X and Y chromosomes coming last

5. Chromosomes
homologous chromosomes - chromosomes that make up a pair - have the same length, centromere position, and staining pattern
both carry genes controlling the same inherited characteristics

6. Example - the homologous chromosomes from the mother and father both carry information about eye color at the same locus
exception to rule in humans - the X and Y chromosomes
females have a homologous pair of X chromosomes, males have XY

7. Meiosis gone wrong
Nondisjunction - happens when two homologous chromosomes move to the same pole during meiosis
one daughter cell is missing a chromosome and another has an extra

8. What happens next? Normal number of chromosomes in gamete is 23
gamete with the extra chromosome will have 24 chromosomes
gamete lacking one will have 22

9. Nondisjunction in Meiosis I or II

10. What happens next?
Gamete with 24 chromosomes joins with a gamete that has 23 chromosomes making a zygote that contains 47 chromosomes
remember: normally the zygote has 46 chromosomes
has 3 copies of one chromosome when it should only have 2
condition is called trisomy

12. Down syndrome
Trisomic disorder in which a zygote receives three homologous chromosomes for chromosome pair number 21
happens in 95% of Down syndrome cases
Philippines example

13. Down Syndrome cont...
Called a syndrome because there are a number of traits that are associated with the condition regardless of race
round, full face,
enlarged and creased tongue, short height, large forehead
rate of Down Syndrome increases with the age of the mother

15. Edward’s Syndrome Trisomy 18 Faun like ears Small ears
Dies within the first few weeks

16. Patau Syndrome
Trisomy 13
Hairlip
Small Head
130 day life span

17. Klinefelter Syndrome (XXY)
Nondisjunction of the sperm or egg cell
child inherits two X chromosomes and 1 Y chromosome
appears to be male at birth but produces large amounts of female sex hormones at puberty
males are sterile

18. Super Male (XYY)
Tall
Aggressive
Acne
Too much testosterone

19. Trisomic Female
Has 3 X chromosomes

20. Or?
Gamete with 22 joins with 23 gamete, final number is 45 (normal is 46)
zygote only has one copy of the lacking chromosome when it should have 2
resulting condition is called monosomy

21. Turner’s Syndrome
Monosomic disorder when sex chromosomes undergo nondisjunction
female with single X chromosome
45 chromosome zygote produced
traits - do not develop sexually, short, widened necks
most miscarried before 20th week
can grow to lead highly productive lives

23. To Do: Do questions 1-6 on page 586 as a class
Do questions 1-12, 18, on page 593 to be handed in