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Karyotype
Puzzle
| By
Kirstin Bittel, Rachel Hughes, and Laura Carsten |
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| Time: |
1 class
period |
| Preparation
Time: |
10-15 minutes
photocopying handouts |
| Materials: |
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
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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://www.nlm.nih.gov/medlineplus/encyclopedia.html
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&rid=gnd
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Activity
Engagement (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. |
Embedded
Assessment |
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