Download Human Genetics: Bug Karyotype Ch. 14

Human Genetics: Bug Karyotype
Name _____________________________
Ch. 14
Period _________ COOK
Background
A karyotype is a picture of the chromosomes of a cell that have been stained so that banding patterns appear. This is
best done during metaphase of mitosis. After staining, the cell is photographed through a microscope, the picture is
enlarged, the chromosomes are cut from the picture, and they are arranged according to size, arm length, centromere
position, and banding patterns. The karyotype that results from this procedure may be used to diagnose some genetic
diseases.
This investigation uses karyotypes for a species of insect to identify four genetic diseases. Using their chromosomes, you
will make karyotypes for six of these insects. One will represent a normal male, one a normal female, and one for each
of the four genetic diseases.
The insect species being studied has three pairs of homologous chromosomes. The first two pairs are autosomes; the
last pair are sex chromosomes. Sex determination is the same as in humans (XX=female, XY=male).
Procedure
1. Cut out the chromosomes for insect #1; pair them according to homologous chromosomes.
2. Using the banding patterns, match the chromosomes and glue them to the data sheet in the same order as the
normal male/female (refer to Figure 1).
3. Make sure the centromeres are on the line when glued to the paper.
4. Repeat 1-3 for the other five insects.
5. Answer the questions to determine which insects are normal and which have the four genetic diseases.
Normal Karyotype
Human Genetics: Bug Karyotype
Ch. 14
Disorders
Size Reduction Disorder
This disorder involves a monosomy of the third pair. An “X” chromosome is missing so that a male has only a “Y” or a
female has only an “X”. The result is a small male or female.
Clear Wing Disorder
This disorder involves a trisomy of the second pair of chromosomes. The result is clear wings. Offspring are sterile.
Duplication Disorder
This disorder is a duplication of part of one of the 1st pair of chromosomes. The part duplicated remains attached to the
chromosome resulting in large chromosomes. The insect has two heads, banded wings, and extra body segments.
Unsegmented Disorder
This disorder is due to a deletion of a segment of an “X” chromosome of the 3rd pair. The result is an “X” chromosome
that is shorter than normal. The insect is reduced in size and has no body segmentation.
Human Genetics: Bug Karyotype
Ch. 14
Bug Lab—Data Sheet
Identify which insects have these 6 conditions by writing the names of the conditions on the lines t the bottom of the
boxes: normal male, normal female, size reduction, clear wing, duplication, unsemented.
Human Genetics: Bug Karyotype
Ch. 14
Post-Lab Questions
1. How many total chromosomes are present in a normal bug karyotype? _____________
2. How many chromosomes are present in each cell of a human? _____________
4. Chromosomes that are NOT sex chromosomes are called autosomes. How many total autosomes are present in a
bug’s normal karyotype? ______________
Body cells are called somatic cells. Somatic cells include the skin, liver, muscle, stomach and other bodily cells in
humans. The term diploid chromosome number refers to the number of chromosomes in a somatic cell. The diploid
number varies from species to species, however it does not differ from somatic cell to somatic cell within the same
organism. To find the diploid number, simply count the number of chromosomes in a normal bug’s karyotype. The
diploid chromosome number is also called the 2n number.
5. What is the diploid chromosome number for a normal bug? _____
6. What is the 2n chromosome number for a normal bug? ____
The HAPLOID CHROMOSOME NUMBER refers to the number of chromosomes in an organisms sex cells. Sperm in males,
eggs in females. The haploid number, or 1n number is always -half- that of the diploid number.
7. What would the haploid chromosome number for a normal bug’s karyotype be? ____
11. Describe two types of information that can be gained about a child before it is born through a karyotype.
a. ________________________________________________________________________________
b. ________________________________________________________________________________
12. How many chromosomes are in a normal human karyotype?
a. 23
c. 46
b. 44
d. 2 (either XX or XY)
13. Which of the following genetic abbreviations denotes a male human?
a. 23, XX
c. 23, XY
b. 46, XX
d. 46, XY
14. Why is the ratio of male to female births roughly 50:50?
a. All egg cells carry an X chromosome.
b. All sperm cells carry an X chromosome.
c. Half of all egg cells carry a Y chromosome.
d. Half of all sperm cells carry a Y chromosome.
15. How are the X and Y chromosomes different?
a. Only one is an autosome.
b. The Y carries fewer genes than the X.
c. The X is smaller than the Y.
d. Only females have a Y.
16. All human cells carry
a. at least one X chromosome.
b. a pair of X chromosomes.
c. at least one Y chromosome.
d. one X and one Y chromosome
Human Genetics: Bug Karyotype
Ch. 14