Karyotype Puzzle
By Kirstin Bittel, Rachel Hughes, and Laura Carsten
Time :
Preparation Time :
Materials :
1 class period
10-15 minutes photocopying handouts
Overhead 1 – Example of normal karyotypes and list of
abnormalities and their medical notation.
Student karyotypes – 1 per pair of students
Abstract
During this lesson students are introduced to human karyotyping as a means to diagnose human
mutation caused by errors during the formation of zygotes or during the process of meiosis.
Purpose – Engagement of students in pairing chromosomes to look for abnormalities in during
the formation of zygotes or during the process of meiosis.
Objectives
Students will be able to:1. Identify chromosome pairs based upon band patterns and location of centromere.
2. Order chromosome pairs based upon size.
3. Differentiate normal karyotypes from abnormal karyotypes.
4. Correctly record karyotype information using correct notation.
National Science Education Standard:
Content Area C – The Molecular Basis of Heredity
- Most of the cells in a human contain two copies of each of 22 different chromosomes. In
addition, there is a pair of chromosomes that determines sex: a female contains two X
chromosomes and a male contains one X and one Y chromosome. Transmission of genetic
information to offspring occurs through egg and sperm cells that contain only one representative
from each chromosome pair. An egg and a sperm unite to form a new individual. The fact that the
human body is formed from cells that contain two copies of each chromosome--and therefore two
copies of each gene--explains many features of human heredity, such as how variations that are
hidden in one generation can be expressed in the next.
- Changes in DNA (mutations) occur spontaneously at low rates. Some of these changes make
no difference to the organism, whereas others can change cells and organisms. Only mutations in
germ cells can create the variation that changes an organism's offspring.
Teacher Background
Sometimes during the processes of meiosis and the creation of gametes and zygotes, errors are
made and individuals are born with additional or missing chromosomes. The word Trisomy in a
disorders name indicates that there are three copies of a particular chromosome instead of two.
Probability of Being Born With Specific Chromosomal Disorders
Trisomy 21 (Down)
Trisomy 18 (Edwards)
Trisomy 13 (Patau)
47,XXY (Kleinfelters)
47,XYY
47,XXX
45,X
1 in 700
1 in 3000
1 in 5000
1 in 1000 males
1 in 1000 males
1 in 1000 females
1 in 5000 females
The most common chromosomal disorder is Trisomy 21, more commonly known as Down
Syndrome. Symptoms of Trisomy 21 include individuals with a broad, flat face, a thick tongue and
a small nose and mild to moderate mental retardation.
Trisomy 18 is also known as Edwards Syndrome and affects girls almost 3 times as often as
boys. Symptoms include: low birth weight, mental retardation, low-set or malformed ears, small
jaw, hand abnormalities, congenital heart disease, hernias, and undescended testicles. 50% of
those born with Trisomy 18 often don’t live past the first few months of life.
Trisomy 13 is also called Patau syndrome. Symptoms include: small eyes with defects in the iris,
cleft lip, cleft palate, and low-set ears. Congenital heart disease is present in approximately 80%
of affected infants. Hernias and genital abnormalities are common. 80% of infants born with
Trisomy 13 don’t survive the first month while survivors have severe mental defects. Rarely does
a child inflicted with Trisomy 13 survive to adulthood.
XXY Syndrome is also referred to a Kleinfelters Syndrome. This disorder affects only boys.
Symptoms include: development of breasts, spare facial hair, and an inability to produce sperm.
XYY Syndrome affects only boys. There are no noticeable physical differences with this disorder.
Symptoms include: increased activity, delayed mental maturity, and in creased tendency for
learning problems in school.
XXX Syndrome is known as Triple or Triplo X. This disorder affects only females. Again, there are
no physical indications of Triplo X. Symptoms include: possible delayed menopause, and
increased probability of delayed development in motor function, speech, and maturation
XO Syndrome is more commonly known as Turner Syndrome and affects only girls. There are
minimal physical abnormalities and Turner’s does not affect intellect. The primary effect of
Turner’s is due to the missing X chromosome. This causes infertility.
Related and Resource Websites
http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html
http://oak.cats.ohiou.edu/~schutte/new_page_1.htm
http://www.genetics.org
http://nlm.nih.gov/medlineplus/encyclopedia.html
http://www.ncbi.mlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&rid=gnd
Activity:
Engage (How do mutations occur at the chromosomal level?)
1. As students enter the room, hand out envelopes with cut karyotypes to each group. Tell them,
“We have been studying the genetics of plants, but we’ll be looking at humans today. All living
organisms on the earth have DNA, genes, and chromosomes. As you know, sometimes things go
wrong and mutations occur at the genetic level. Errors can also occur during meiosis as an
organism creates gametes. Sometimes extra chromosomes are copied, other times they are
deleted in part or altogether. These errors mean that after conception, the organism has too many
or too few chromosomes and often cannot live long enough to be born. Other times, organisms
are born with physical, mental, or physiological abnormalities. Today you will play the role of a
geneticist. You have been given the chromosomes for an individual and will construct a karyotype
to look for chromosomal abnormalities. A karyotype is made by photographing cells in mitosis
when chromosomes are condensed and easy to see. “
2. They, then cut out the individual chromosomes and match them with their counterparts, and
looking for any extra or missing chromosomes. “You will need to match the chromosomes in your
envelope and order them by size. The longest chromosome is called number 1 and the shortest is
called number 22. The last pair of chromosomes is the sex chromosomes. As you recall, the X
chromosome is longer than the Y chromosome. If you need help, refer to the overhead. Good
Luck”
3. Allow students a good bulk of the class period to work with their lab groups to match
chromosome pairs and rank them in order of size. Once their order is correct have them glue their
karyotypes to a clean sheet of paper.
4. Bring the class together and introduce the correct annotation for genetic information. Genetic
information is written with the number of chromosomes, the sex chromosomes and extra
chromosomes listed by number. For example a normal female’s genetic data is written as 46XX
while a male with Trisomy 13 is recorded as 47XY+13. Once they know the genetic data, they
should check the list on the overhead and record the genetic disorder of their patient. Students
should add genetic information and the disorder on their karyotype.
5. Have students present their findings to the class. They need to share the genetic data on their
patient and provide evidence from the karyotype to support their claim. As they share their
genetic data, students should speculate on how the addition of certain chromosomes (or
deletions) might affect an individual. While this might be difficult for students whose patient had
Trisomy 13 or 21, it should be easier for those who have disorders related to the sex
chromosomes. Allow others groups to speculate on the possible ramifications after groups have
presented their initial ideas.
6. Check to see if each group correctly matched their chromosomes and if they were able to
correctly identify the disorder expressed by the patient. Students with exceptional understanding
of mutations at the chromosomal level should be able to determine possible ramifications of the
mutations.
Homework
Students can research the disorder of their patient and report back to the class at a later time.