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NEL Cell Division 585

Section17.4

Figure 5shows the incomplete karyotype chart of a human. Notice that several

chromosomes are missing. Identify where chromosomes a to f (Figure 6) should be in

this karyotype chart.

SAMPLE exercise 1

12 3 4 5

67 89101112

13 14 15 16 17 18

19 20 21 22 X Y

Figure 5

abcdef

Figure 6

Solution

1. Start by scanning the karyotype chart to see which pairs are missing a chromosome.
   Pairs 3, 5, 8, 15, and 16 need a partner.


2. Match the most obvious chromosomes first: the longest, shortest, or most distinctively
   banded chromosomes.


3. For chromosome matches that are not as obvious, look carefully at the banding pattern
   and location of the centromere.

Amniocentesis

A diagnostic technique known as

amniocentesis can be used to test

for nondisjunction and other

genetic disorders in developing

fetuses. During this procedure, a

fine needle is inserted into the

amniotic sac that surrounds the

fetus, and about 10 mL of the

amniotic fluid in which the fetus is

bathed is withdrawn. This fluid

contains fetal cells that can be

used to produce a karyotype

chart, as well as chemicals that

may signal specific disorders.

DID YOU KNOW??

Learning Tip

You can also construct a

karyotype chart using a copy

of the chromosome images.

For the Sample Exercise and

Practice question 1, copy

Figures 5, 6 and 7. Then, cut

out the chromosome images in

Figures 6and 7 , and position

them on Figure 5according to

their size, shape, and banding

patterns.

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