Biology-Mr.Willets
Human Karyotype
If a person is suspected of having a chromosomal abnormality (such as a trisomy or a monosomy or missing pieces of chromosomes), this can be checked by examining the person's chromosomes. When a person's chromosomes are photographed and the pictures of the homologous pairs are arranged by size, the result is called a karyotype.
The diagram available is a karyotype of a normal male. (Click here to see karyotype) You will notice that there are 22 matched pairs (autosomes) and one mismatched pair (the X and the Y- the sex chromosomes). Pair # 1 is the largest and pair #22 is the smallest. Besides using size to match members of a pair, the location of the centromere is also used. When the chromosomes are put on the karyotype form, the centromere is placed on the dotted line.
In order to photograph the chromosomes, they must be visible under the microscope. This only occurs during cell division. The process starts by getting some living cells from the person- white blood cells do nicely. These cells are treated with chemicals to make them divide and the process is stopped at metaphase. The cells are then put on a slide in such a way as to make the chromosomes spread out. A photograph is taken of the chromosomes. It is enlarged and individual chromosomes are cut out and arranged as on the back.
This karyotype can then be examined for any abnormalities.
This process can be used to examine the chromosomes of an unborn child if cells from the fetus can be obtained. Two methods of getting fetal cells are: amniocentesis and chorionic villi sampling (CVS).
EXTRA CREDIT
A drawing is available of human chromosomes spread out as they would appear as a result of the procedure described above. Click Here to Go to Chromosome Drawing This drawing is simplified to make your job easier. You must cut the chromosomes out and arrange them by pairs on the blank karyotype form. The largest pair is #1 and so on. Use the size of the chromosomes, the location of the centromere and the banding pattern to match the homologous pairs. A key showing what each chromosome looks like is included. If we were using an actual photograph of chromosomes, it would be much more difficult to match the pairs.
I suggest finding a quiet place (with no breezes) to work. Enlist the aid of a younger brother or sister. They are good at cut and paste stuff. You do not have to cut out each chromosome perfectly. It is easier if you leave some of the white area around it and make each cut a rectangle. Line them all up before you paste any of them on the sheet. Remember to put the centromere on the dotted line on the karyotype form. Keep your eye out for any abnormalities!!! Good Luck!!