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Activity 2-1: Karyotyping - A Chromosome Portrait

PLAN

Summary Students construct a karyotype by arranging chromosomes in pairs according to size, shape, and position of the centromere. Students analyze the karyotypes to distinguish differences among the chromosomes, including the sex (X and Y) chromosomes.

Objectives

Students:

\checkmark arrange paper chromosomes in pairs according to chromosome size, shape, and position of the centromere.

\checkmark identify distinctive characteristics of each chromosome.

\checkmark explain how karyotypes are used to detect genetic disorders.

Student Materials

  • Resources 1 or 2, and 3
  • Activity Report
  • Scissors
  • Metric ruler
  • Glue or tape

Teacher Materials

  • Activity Report Answer Key
  • Extra student materials
  • Resource 4 and Map of the Human Genome (Optional)

Human Genome Project addresses:

DOE sites

http://www.er.doe.gov/production/ober/hug_top.html

http://www.ornl.gov/TechResources/Human_Genome/home.html

http://www.ornl.gov/hgmis/links.html

NIH site: National Human Genome Research Institute

http://www.nhgri.nih.gov/

Helpful Hints

  • Provide an envelope for cutout chromosomes in case some students do not finish in one class period.
  • Resources 1, 2, and 4 should each be printed on different colored paper. If possible, use card stock.
  • Check that students record the letter of the “squash” sheet on their human karyotype form sheet.
  • For additional research, students can use the Human Genome Project Website to explore its progress and find out how many human genes have been identified and their location.

Advance Preparation

Copy Resources 1-3 and the Activity Report.

Refer to Enrichment 4-1: Chromosome Cards to see the actual ordering of chromosomes 1-22 and the sex chromosomes. You might have these pages available in the classroom, so students can check their completed karyotypes against them.

Optional: Review Resource 4, Down syndrome karyotype, to decide whether or not to assign this optional activity. You can copy Resource 4 for students and/or make a transparency of this karyotype.

Optional: Arrange for guest speaker such as a genetic counselor.

Estimated Time One class period

Interdisciplinary Connections

Art Make posters of the karyotypes or collages of chromosomes for display.

‘Prerequisites and Background for the Teacher’

Down syndrome is a genetic condition that affects 1 out of 800 live births. People with Down syndrome have an extra portion of chromosome 21 in some or all of their cells. The extra copy of some or all of chromosome 21 results in over-expression of those genes and increased production of certain gene products. Down syndrome is usually caused by non disjunction, a failure of sister chromatids to separate during meiosis. In this case, during anaphase I both members of the pair of chromosome 21 migrate to the same side of the cell resulting in either a gamete with no copies of chromosome 21 or a gamete with two copies of chromosome 21. If the gamete with two copies of chromosome 21 is fertilized (or fertilizes) then the resulting zygote will have three copies of chromosome 21, a condition known as Trisomy 21.

Down syndrome also can be caused by translocation, where a piece of a chromosome breaks away and attaches to another chromosome. In Down syndrome, translocation usually occurs between chromosomes 14 and 21. These individuals have two normal chromosomes 21 plus an extra piece of chromosome 21.

Finally, in a small percentage of cases, Down syndrome can be caused by a mosaic chromosomal makeup where some of the cells contain the normal number of chromosomes and some cells contain 47 chromosomes.

The extra genetic material that results in Down syndrome can come from either parent, but in 95% of the cases it comes from the mother. Although a Down Syndrome child can be born to a mother of any age, the risk greatly increases over 35 years of age.

Children with Down syndrome often have low muscle tone, increased incidence of congenital heart defects and leukemia, respiratory problems, some degree of impaired intelligence, and abnormalities of the hands, eyes, ears, and tongue.

IMPLEMENT

Introduce Activity 2-1 by reading the introduction and discussing the information about karyotyping in the student edition.

Step 1 Remind students to keep track of their chromosome pieces.

Step 2 Have students finish Resources 1 and 2 and fill out Resource 3. Then make sure they complete the Activity Report.

Extend Activity 2-1 by showing students a karyotype of Down syndrome (Resource 4). This is optional. Ask students to identify any difference between Resource 4 and the karyotypes from Activity 2-1. Students should recognize that the Down syndrome karyotype contains three copies of chromosome 21.

ASSESS

Use the completion of the activity and the written answers on the Activity Report to assess if students can

\checkmark arrange paper chromosomes in pairs according to chromosome size, shape, and position of the centromere.

\checkmark distinguish distinctive characteristics of each chromosome.

\checkmark explain how karyotypes are used to identify genetic disorders.

Activity 2-1: Karyotyping - A Chromosome Portrait Activity Report Answer Key

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. Name three ways human chromosome pairs are different from one another.
  2. Describe the difference between a normal male and a normal female karyotype.
  3. What reasons might a health professional have for wanting a karyotype of a person's chromosomes?

The person who makes karyotypes is called a cytotechnologist. (Cyto is the Greek word for cell; technologist comes from the Greek word meaning art.) In Activity 2-I you did some of the things a cytotechnologist does. Find out what some of the jobs of a cytotechnologist are. Do you think you would want to be a cytotechnologist? If not, why do you think someone else might want to be a cytotechnologist? In a paragraph, explain why you would or would not want to be a cytotechnologist.

Review Questions/Answers

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. Explain three facts that scientists know about chromosomes.
  2. Chromosomes exist in pairs with one exception. Describe that exception.
  3. What is a karyotype? How is it made? How is a karyotype useful in the study of genetics?

Activity 2-1 Resource 1: Karyotyping - A Chromosome Portrait (Student Reproducible)

Activity 2-1 Resource 2: Karyotyping - A Chromosome Portrait (Student Reproducible)

Activity 2-1 Resource 3: Karyotyping - A Chromosome Portrait (Student Reproducible)

Activity 2-1 Resource 4: Karyotyping - A Chromosome Portrait (Student Reproducible)

Activity 2-1 Report: Karyotyping - A Chromosome Portrait (Student Reproducible)

1. Name three ways human chromosome pairs are different from one another.

a.

b.

c.

2. Describe the difference between a normal male and a normal female karyotype.

3. What reasons might a health professional have for wanting a karyotype of a person's chromosomes?

Image Attributions

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Grades:

6 , 7 , 8

Date Created:

Feb 23, 2012

Last Modified:

Feb 23, 2012
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