1. Notes: Karyotypes s

2. Human Chromosomes- what you know…
Humans have 46 chromosomes (diploid-2N)
2 of them are sex chromosomes (X and Y) they determine what sex you are
XX = female
XY = male
44 of them are autosomes  they do not determine the sex of an individual.
Sex chromosomes

3. How is a KARYOTYPE Made? Collect sample:
Fetus: amniotic fluid collected during an amniocentesis or a piece of the placenta collected during a chorionic villi sampling test (CVS).
Newborn: white blood cells
Separate dividing & non-dividing cells using chemicals
Culture the dividing cells to get a lot of cells
Add chemical to stop cell division when chromosome is compacted
Lyse the cells
Stain the chromosomes (stain sticks to regions with a lot of “A” and “T” bases
Analyze!

4. How is a KARYOTYPE Analyzed?
Use computers to match the homologous pairs.
We will cut out the chromosomes from a chromosome spread then arrange them to match the banding patterns of the homologous pairs
Use banding patterns, size of chromosome, and position of centromere
This type of picture is called a
KARYOTYPE

5. Chromosome Spread

6. Karyotype

7. What does a Karyotype tell you?
Sex (male or female)
Irregular numbers of chromosomes
Any mutations in the chromosomes
Basically: all the chromosomes in a cell are displayed and can be examined for abnormalities

8. Is this offspring a girl or boy? How do you know?

9. Are there any abnormalities in this offspring?

10. Chromosomal Disorders
Most of the time, the mechanisms that separate human chromosomes in meiosis work very well, but things can go wrong
The most common error: NONDISJUNCTION
The chromosomes fail to separate in Anaphase I or II
The result? Abnormal numbers of chromosomes in gametes.

11. Nondisjunction Prefixes: dis = absence of / opposite of non = not
Root Word:
Junction = joining together
disjunction = the act of separating
nondisjunction = the act of not separating

12. End of Meiosis—4 gametes produced
Metaphase I
Figure 14-15
page 352
“Trisomy” = 3 copies of
a chromosome
Nondisjunction
(after anaphase I)
End of Meiosis—4 gametes produced

16. Examples of Chromosomal Disorders
Down Syndrome (3 #21 chromosomes)
Klinefelter’s Syndrome (XXY)
Turner’s Syndrome (XO)
Triple X Syndrome (XXX)
                

17. Examples of Nondisjunction resulting in Chromosomal Disorders
Down's Syndrome: 47 chromosomes with 3 #21 chromosomes.
Triple-X Syndrome: 47 chromosomes caused by 3 X chromosomes.
Klinefelter's Syndrome: 47 chromosomes caused by 2 X chromosomes and 1 Y chromosomes.
Turner's Syndrome: 45 chromosomes with 1 X chromosome (caused by the absence of one of the X chromosomes or a Y chromosome).

18. Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation

19. Chromosomal Mutation (change in number)
If an organism is born with the incorrect number of chromosomes
Ex: 47 human chromosomes instead of 46
Result of nondisjunction

20. Down Syndrome 3 copies of chromosome #21
1 in 800 babies in the US is born with this disease
produces mild to severe mental retardation
May not live as long

21. Klinefelter’s Syndrome
This is a sex chromosomal disorder associated with males.
Nondisjunction causes an extra X chromosome to be passed along during meiosis (XXY).
Resulting male cannot reproduce
Cases have been found in which individuals were (XXXY) or (XXXXY)
Decrease muscle mass and body hair

22. Turner’s Syndrome
This is a sex chromosomal disorder associated with females.
Nondisjunction causes offspring to inherit only one X chromosome (genotype = XO).
Resulting female is sterile due to underdeveloped sex organs.
1/2500 females

23. Review question.. Who determines the sex of a child?
The mother or the father?
THE FATHER!!!!
Why?

24. Why does the father determine the sex of the offspring???
Mom is XX: she can donate either one X chromosome or the other X chromosome to the offspring
(mom can only donate an X)
Dad is XY: he can donate either an X chromosome or a Y chromosomes.
If the offspring receives an X from dad, it is female
If the offspring receives a Y from dad, it is male