This simple model allows the students to identify the parts of a chromosome. The two identical chromatids and the centromere are clearly differentiated in this model.
1 pipe cleaner for each chromosome
1 bead for each chromosome
Cut the pipe cleaner in half. Press down the cut ends of the pipe cleaner with the point of a pencil so that they are not sharp.
Place the two halves of the pipe cleaner together.
Place both pipe cleaner halves though the bead.
Move the bead approximately to the center of the pipe cleaner halves.
Repeat Steps 1 through 4 for each chromosome to be made.
The simplest use for this model is in describing the structure of the chromosome. Chromosomes appear only immediately prior to cell division and are made up of 2 exact copies of genetic material (chromatids).
As students of biology are learning about the structure of the chromosome, present this model in addition to any raised lines that the text provides. The chromosome is composed of two identical chromatids attached at the centromere. Ask the student the following questions:
Using the model, where is the centromere? (The bead)
Using the model, where is a chromatid? (one pipe cleaner- one side of the chromosome)
Using the model, where is a chromosome? (The entire model)
This model will be also be useful in describing the movement of chromosomes during cell division. Following the stages of mitosis during instruction, this model can be set up to mimic the pictures in the book. For instance the following picture is of the chromosomes during metaphase.
This model can be used in 2 colors for low vision students to indicate homologous chromosomes. These are chromosomes containing the same genetic content and that are the same size and shape. Individuals receive one homologous chromosome from each parent.
High School – Inheritance and Variation of traits
LS3.A: Inheritance of Traits
Each chromosome consists of a single very long DNA molecule, and each gene on the chromosome is a particular segment of that DNA. The instructions for forming species’ characteristics are carried in DNA. All cells in an organism have the same genetic content, but the genes used (expressed) by the cell may be regulated in different ways. Not all DNA codes for a protein; some segments of DNA are involved in regulatory or structural functions, and some have no as-yet known function. (HS-LS3-1)
LS3.B: Variation of Traits
In sexually reproducing organisms, each parent contributes half of the genes acquired (at random) by the offspring. Individuals have two of each chromosome and hence two alleles of each gene, one acquired from each parent. These versions may be identical or may differ from each other. (MS-LS3-2)