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Karyotype Puzzle
By Kirstin Bittel, Rachel Hughes, and Laura Carsten

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
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

 

 

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



PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:


an
NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award

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Supported by NIEHS grant # ES06694


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Last update: November 10, 2009
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