Refer to Chapter 11 for Lab Procedure pg. 867
CH11: Karyotype Lab
Discovery Question: What does a karyotype show about chromosomes and how failure in
meiosis affects the chromosome numbers in gamete?
Humans have 46 chromosomes in every diploid (2n) somatic cell. The
chromosomes of a diploid cell occur in homologous pairs, which are pairs of
chromosomes that are similar in size, shape, and the position of their centromere. In
humans, the 22 homologous pairs of chromosomes that house all genes not related to
sex are called autosomes. The twenty-third pair, which determines the individual’s sex,
makes up the sex chromosomes. Females have only one type of sex chromosome in
their pair, which is the X chromosome. Males have two types of sex chromosomes, an
X chromosome and a much smaller Y
chromosome. The figure below shows each of
the 22 types of autosomes and the 2 types of
sex chromosomes.
A karyotype is a diagram that shows a
cell’s chromosomes arranged in order from
largest to smallest. A karyotype is made from a
photomicrograph (photo taken through a
microscope) of the chromosomes from a cell in
metaphase. The photographic images of the
chromosomes are cut out and arranged in
homologous pairs by their size, shape, and
banding pattern. The karyotype can be analyzed
to determine the sex of the individual and
whether there are any chromosomal
abnormalities. For example, the karyotype of a
normal female shows two X chromosomes, and the karyotype of a normal male shows
an X chromosome and a Y chromosome. Abnormalities would show up in any
combination of chromosomes different than the normal 44 autosomes and 2 sex
chromosomes.
Chromosomal abnormalities often result from nondisjunction, the failure of
chromosomes to separate properly during meiosis, specifically during anaphase I or
anaphase II. Nondisjunction results in fetuses that inherit too many or too few
chromosomes in their cells. Trisomy is a specific abnormality in which a zygote has an
extra chromosome, or section of a chromosome. This means that the cell contains 47
chromosomes instead of 46. Down syndrome, or trisomy 21, is a chromosomal
abnormality that results from having an extra number 21 chromosome. This extra
chromosome means too many genes and variable developmental problems generally
ensue due to genes interference.
In this lab, you will produce and analyze a karyotype of chromosomes from a
fetus to determine the sex of the fetus and whether or not the fetus has Down
syndrome. From this you will give ideas as to what could happen if other chromosome
abnormalities would arise.
Refer to Chapter 11 for Lab Procedure pg. 867
Do not write on this sheet! Answer on a separate sheet of paper stapled to your karyotype.
1. Write down your chromosome spread letter from the lower right of your paper.
2. Carefully cut each chromosome from the chromosome spread in Figure 2. Be sure to leave a slight
margin around each chromosome. Be careful not to lose any!
3. Arrange the chromosomes in homologous pairs. The members of each pair will be the same length,
have similar banding, and will have the centromere in the same location. Use the ruler to measure the
length of the chromosome and the position of the centromere. Arrange the pairs according to their
length, from largest to smallest. Be careful to note the ‘X’ & ‘Y’ chromosome.
4. Tape or glue each homologous pair to a human karyotyping form, (a blank spread) positioning the
centromeres on the same lines. Place the pairs in order, with the longest pair at position 1, the shortest
pair at position 22, and the sex chromosomes at position 23. Again, be careful for the sex chromosomes.
5. The diagram you have made is a karyotype. Analyze the karyotype to determine the sex of the
individual and whether or not the individual will have a chromosomal abnormality (and what it is).
6. Clean up your materials before leaving the lab.
7. Answer the following questions in pairs on a separate sheet or on the back of the spread.
Questions: Answer all questions in complete sentences. You need one answer sheet per group.
1. What is your karyotype spread letter?
2. How many chromosomes do you have in your karyotype?
3. What is a HOMOLOGOUS PAIR and how many does your karyotype have?
4. What are AUTOMSOMES and how many are present?
5. What are SEX CHROMOSOMES and how many does your karyotype have?
6. What is a chromatid and how many chromatid does your karyotype have?
7. What is the haploid number for this organism? n = ____
8. What is the diploid number of this organism? 2n = ____
9. Does your karyotype reveal an abnormality? (Yes or No). IF YES, describe it.
10. What sex is the organism?
11. Find and copy down a diagram of NON-DISJUNCTION to explain how chromosomal
abnormalities might occur in organisms.
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