1. Errors in Meiosis

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

5. Normal Male
Normal Female

6. What is Non-Disjunction?
Process where homologous chromosomes or sister chromatids do not separate during meiosis (anaphase I or anaphase II).
Non-disjunction produces gametes that have too many (trisomy) or too few chromosomes (monosomy).

8. Non-Disjunction 22 23 23 24 45 47
monosomy
trisomy

9. 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

10. Down Syndrome Most commonly known as trisomy 21
1:700 births; 1 in 6 die within 1st year
Average age is 16.2 years

11. Down Syndrome
Prone to heart defects, respiratory problems and leukemia
Odds of having a Down’s child increased 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. Down Syndrome Common facial feature Short stature
Stubby fingers and toes
Large tongue – makes speech difficult
Mental disability (IQ is in the range)

13. XXX (Super Female) 1:1000 live births Normal intelligence
Fertile (able to have children)
No physical problems

14. Klinefelter’s Syndrome
XXY
Affects 1:500 males
Tall, sterile males (not able to produce children)
Normal intelligence
Has female characteristics

15. Jacob’s Syndrome (super male)
XYY
Somewhat taller than average
Slightly below normal intelligence
1:1000 males
Extra testosterone

16. Homework
Read pg
Pg. 166 #1, 3, and 9
Study for Meiosis Quiz