Chromosome Models -- Karyotyping

Purpose:

To provide a tactile opportunity for students with visual impairments to construct a karyotype, an organized model of an organism’s chromosomes, showing the chromosome’s size and shape

Background information

Chromosomes in a cell are randomly arranged, except during cell division. To study chromosomes, scientists photograph the chromosomes while the cell is in the process of replicating. The scientists will then cut out the pictures of the chromosomes and organize them into pairs according to size and shape. A popular classroom activity is to give students photographs of human chromosomes and ask them to develop a karyotype. For a student who lacks the vision to see photographs, the clay chromosomes provide a tactile alternative. The number of chromosomes in an organism’s cells varies depending on the species of the animal. For example, the house fly has only 12 chromosomes.

Materials

4 to 6 ounces of play dough or clay depending on the number of chromosomes needed. Play dough works well because it hardens and the “chromosomes” then hold their shape.
Smooth clean surface at least 12” by 12”. A tray works well to define the space.
Raised line images of karyotypes, some unsorted and others organized into a karyotype.

Preparation

If time allows the students can be involved in the preparation of the chromosomes by creating a variety of short snake like shapes of various lengths and thicknesses. 26 pairs of chromosome models are needed to create a human karyotype. However, this is very time consuming depending on a student’s hand skills. It is usually a better use of the student’s time to have pre-made chromosomes ready. Also, it is very time consuming to sort and tactually identify 26 pairs of chromosomes. The same concepts can be taught using a karyotype of an organism that has fewer chromosomes than a human.

Procedure

Prepare “Chromosomes” prior to the lesson.
After listening to class discussion about karyotypes, and reading the lesson, the student examines tactile pictures of chromosomes both in random order and as a karyotype.
Given a tray of chromosome models in random order, the student organizes the chromosomes by size and shape from largest to smallest. The sex chromosomes are placed at the end of the chromosome arrangement.
This activity could also be done using chromosomes made of heavy paper, sorted then taped to the tray to prevent movement.
Follow up discussion would include some of the factors that scientists look for in a karyotype including missing chromosomes and extra chromosomes.

NGSS Standards

LS1.B: Growth and Development of Organisms

In multicellular organisms individual cells grow and then divide via a process called mitosis, thereby allowing the organism to grow. The organism begins as a single cell (fertilized egg) that divides successively to produce many cells, with each parent cell passing identical genetic material (two variants of each chromosome pair) to both daughter cells. Cellular division and differentiation produce and maintain a complex organism, composed of systems of tissues and organs that work together to meet the needs of the whole organism. (HS-LS1-4)