1. KARYOTYPING AND NON-DISJUNCTION
Please take out your Gizmo worksheet and vocabulary sheet

2. Learning Goals Understand what a karyotype is and how to analyze it
Learn about symptoms of various syndromes
Understand the process of nondisjunction and how it explains the genetic basis of various syndromes

3. Agenda for Today Take up Gizmo Lesson on Karyotyping
Playdough activity
Lesson on nondisjuction
Nondisjunction worksheet
Reading on Gregor Mendel

4. What is karyotyping?
A picture of a cell’s complete set of chromosomes grouped together in pairs and arranged in order of decreasing size
Pictures of chromosomes are taken as the cell undergoes mitosis (metaphase)

5. Types of Chromosomes Sex Chromosomes Autosomal Chromosomes
One of two chromsomes that determine an individuals sex
In humans and most mammals the two sex chromosomes are the X and Y
Females: XX Males: XY
Autosomal Chromosomes
A chromosome that is not a sex chromosome
Humans have 22 pairs of autosomal chromosomes

6. How do the X and Y Chromosomes Compare?
X is larger than Y
X chromosome contains about 1,000 functioning genes while the Y chromosome only has about 80
WHY??

7. How do the X and Y Chromosomes Compare?
They Y chromosome is only carried by approximately 50% of the population. Therefore, it cannot carry genes that are necessary for an individual's survival. The genes on the Y chromosome code for only male-specific traits

8. Preparing A Karyotype Harvested cells are first cultured
The cells are then treated with colchicine which arrests the cells in metaphase, and then treated and stained to observe the chromosomes
Chromosomes can be photographed or visualized using a computer, and then analyzed
Chromosomes are identified by size, position of the centromere, and banding and staining regions

9. Preparing A Karyotype

10. A mess of chromosomes…

11. Analysis of a Karyotype
The analysis involves comparing chromosomes for their:
Length
Placement of centromeres (areas where the two chromatids are joined)
Banding pattern.

12. After karyotyping… a normal
male

13. After karyotyping… a normal
female

14. What is wrong with this picture?

15. Down’s syndrome

16. Down’s Syndrome Most commonly known trisonomy 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

17. 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

18. What is wrong with this picture?

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

20. What is wrong with this picture?

21. Klinefelter’s Syndrome
Affects 1:500 males
XXY
Tall, sterile males
Normal intelligence
Has female characteristics

22. Klinefelter’s Syndrome

23. What is wrong with this picture?

24. 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

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

26. XXX (super female?) 1:1000 live births Normal intelligence Fertile
No physical problems
What is the sex of this person?

27. How Do These Disorders Occur?
You have 10 minutes to complete the following activity. Working in your table groups:
Obtain a handful of 2 colours of playdough (do not mix them)
Build 2 different coloured homologous, replicated chromosomes
Using your chromosomes simulate meiosis
Where does meiosis need to go wrong in order to end up with a monosomic or trisomic disorder. There are two possibilities.

28. Non-disjunction
Non-disjunction is a failure of chromosomes to properly separate during either Stage 1 or Stage 2 of meiosis
Upon fertilization the zygote may have one too many chromosomes ( trisomy) or one too few chromosomes (monosomy)

29. 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