1. Karyotypes
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2. Meiosis
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3. What happens when things go wrong?
If chromosomes don’t separate during Meiosis I, aneuploidy can occur. This is when a cell has one extra chromosome or is missing one chromosome.

4. Down Syndrome The most common example of aneuploidy.
One of the two gametes carries 2 copies of chromosome 21.
When the zygote forms, it carries 3 copies of chromosome 21.
AKA Trisomy 21.

5. What causes it?
Sperm cells develop in males constantly (beginning at puberty).
Female gametes develop before birth.
At birth, they are called primary oocytes in Prophase I. They stay in this phase until ovulation.
For a 20 year old woman, her egg cells have collected 20 years of damage (chemicals, radiation, etc.)
For a 40 year old woman, the cells have 40 years of damage and the chance of non-disjunction is increased.

6. To analyze chromosomes, scientists photograph cells during mitosis.

7. Then they cut out the photographs of the chromosomes and group them in pairs.
These chromosomes have been stained with Giemsa

8. A completed Karyotype

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Karyotype
* A picture of the chromosomes arranged in pairs by size
* First 22 pairs are called autosomes
* Last pair are the sex chromosomes
* XX female
* XY male
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10. Using karyotypes.
Scientists use karyotypes to help diagnose genetic disorders.
They take embryonic cell samples
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11. Prenatal Testing – 2 tests
Chorionic villus sampling
Done at weeks of pregnancy
Takes a sample of the chorionic villi (they have cells that originally came from the zygote).
Amniocentesis
Done at 16 weeks
Takes a sample of amniotic fluid (it contains fetal cells)
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13. Genetic Disorders Down Syndrome – an extra 21st chromosome.
Turner Syndrome – only one X chromosome
Klinefelter’s Syndrome – XXY chromosomes

14. Genetic Disorders Problem Name of Disorder Results Extra #13
Patau Syndrome
Brain defects; 1:5000 live birth
Extra #18
Edward’s Syndrome
All organ abnormalities, 1:10,000 live birth
Extra #21
Down Syndrome
Unique facial features, shorter limbs, mild mental retardation
Only one X X
Turner’s
Low fertility, many health issues
Extra X XXY
Klinefelter’s
Low fertility, lanky body, many health issues
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15. Normal Male
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2n = 46

16. Normal Female
2n = 46
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17. Female Down’s Syndrome
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18. Down Syndrome (extra 21) Decreased cognitive development Shorter limbs
Eyelid fold
Flatter nose
More common for mothers over 40 years old.

20. Klinefelter’s Syndrome
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21. Klinefelter Syndrome (extra X)
The most common sex chromosome disorder.
Males get it.
Low fertility
Less testosterone production
Lower language development
Tend to be lanky.

22. Turner’s Syndrome
2n = 45
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23. Turner’s Syndrome (one X)
Occurs in females.
Low fertility
Many health problems.

24. Patau Syndrome (extra #13)

25. Patau Syndrome Most embryos do not survive
Very few survive past 1 year.
Mental/motor retardation
Brain, heart, anatomy problems.

26. Edward’s Syndrome (extra #18)

27. Edward’s Syndrome Very low survival rate. Heart abnormalities
Affects all internal organs.

28. You are going to be the scientist!
You will make a karyotype!
You will need: 1. one set of chromosomes
2. a blank piece of paper (put both names on it).
3. scissors
4. glue
5. Reference Sheet
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29. Procedure: Label the blank paper 1 through 23.
Cut out ONE chromosome at a time.
Glue them on the blank paper, by size and shape, using the reference sheet.
You will have 2 for each number. Remember there are 46 chromosomes, or 23 pairs.
Determine the genetic disorder and the gender.
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30. Make sure you’ve written down: a. the disorder b. the gender
c. ALL your names!
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31. Summary
How does a karyotype help scientists determine genetic disorders?
Write at least 5 complete sentences.
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