Modeling Chromosomal Mutations

By Laura Hospitál on Jan 09, 2015

Various types of mutations can occur in chromosomes.  These include mutations in which a portion is deleted, inverted, or duplicated.  In addition,  a portion of  one chromosome can be attached to a nonhomologous chromosome.   The following activity allows the student with a visual impairment to gain a clearer understanding of the manner in which this occurs.  This activity is adapted from the Holt Biology textbook that I have taught from for the past 7 years.  

George Johnson, PhD. And Peter Raven PhD., Biology, 2004, Holt, Rinehart, and Winston

This model was designed by Adele Hauser.

Pictures by Ditmar Hospitál

 

Preparation:

1. Using the hot glue gun, glue the 8 clothespins to the thin flat piece of wood at regular intervals so that the clip portion of each clothespin  hangs off of the wood in the same direction.  The clothespins should open up and away from the wood.  (Refer to the picture).

2. If the student is a large print student, prepare cards as follows:

            a. Cut the cardstock into 9 rectangles with dimensions of 2.5” by 3.5”

            b. Label the cards 1-8 and 40

            c. Repeat b and c to produce to sets of cards.

3. If the student is a braille student, prepare the cards as follows:

a. Using a piece of braille paper and a Perkins Brailler, space down 6 times and space over 5 to write  #1.  Then space over 10 and write #2 and space 10 more and write #3.  Space down 8 lines and continue with #4 to #6 again leaving 10 spaces in between numbers.  Continue by spacing down 8 lines and writing #7,#8, and #40 in a similar manner.  This will produce 2.5” by 3.5” rectangles with one number on each card, a total of 9 cards.

b. Cut out the 2.5” by 3.5” cards with the braille numbers  in the bottom center part of each card.  The shorter sides of the rectangles are the top edge of the paper and the longer sides of the rectangles are the side edges of the braille paper.

c. Repeat b and c  to produce two sets of identical cards.

 

Materials

  • 8 regular wooden clothespins (not the rounded type used for Christmas ornaments)
  • Thin piece of light wood (balsa works well) 2" X 24"
  • Hot glue gun
  • Glue stick for hot glue gun
  • White cardstock paper (See variations also)
  • Perkins Brailler
  • Braille paper
  • Permanent marker - Black
  • Pair of scissors
 

Procedure

As students of biology are taught about chromosomal mutations, this model can be introduced to solidify the concepts taught.

1. Give the model to the student with genes in order , 1-8 on the chromosome. 

2. Give the students an envelope with the second set of genes in order as well including the 2- #40 cards. Explain that the #1-#8 genes are the corresponding genes from the homologous chromosome and that #40 is from a nonhomologous chromosome. 

3. Tell students that this model is of a VERY small portion of a chromosome and that the numbers represent genes. 

4. Have students model the 4 types of mutations by manipulating the note cards.  Only provide assistance as necessary.

a. Deletion - remove one of the "genes" and reconnect the remaining numbers.  For instance if 5 is deleted the result will be "1-2-3-4-6-7-8"

b. Duplication - a fragment attaches to a homologous chromosome - For instance genes 2 and 3 attach from the homologous chromosome to the model after genes 2 and 3 from the model.  (This will require removing 7 and 8 temporarily.)  The chromosome segment would be "1-2-3-2-3-4-5-6" Explain to the students that 7 and 8 have not gone away but that they just won't fit on this model.'

c. Inversion - A fragment inverts and reattaches in a reverse orientation.  For instance if 3-4 inverted, the result would be "1-2-4-3-5-6-7-8" (See picture.)

d. Translocation - A piece of chromosome which has been deleted from one chromosome, reattaches to a nonhomologous chromosome.  As 40 is the only gene from a nonhomologous chromosome, this gene is the only appropriate gene to insert.  Have the student think about this prior to assisting.  The chromsome would have 40 inserted at some point for instance, "1-2-40-3-4-5-6-7" Again, the #8 chromosome will have to be removed.  Explain to the student that this is only due to space on the model. 

This is a picture of the inversion mutation described shown utilizing the model.

Model of an inversion mutation as described in the procedure.

 

Variations

If black on white is not a good color scheme for the student, the colors can, of course, be modified.  The picture of this model shows a black on yellow color scheme. 

 

NGSS Standards:

High School - Inheritance and Variation of Traits

LS3.B: Variation of Traits
In sexual reproduction, chromosomes can sometimes swap sections during the process of meiosis (cell division), thereby creating new genetic combinations and thus more genetic variation. Although DNA replication is tightly regulated and remarkably accurate, errors do occur and result in mutations, which are also a source of genetic variation. Environmental factors can also cause mutations in genes, and viable mutations are inherited. (HS-LS3-2)

 

Middle School - Growth, Development, and Reproduction of Organisms

LS3.A: Inheritance of Traits - Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. Each distinct gene chiefly controls the production of specific proteins, which in turn affects the traits of the individual. Changes (mutations) to genes can result in changes to proteins, which can affect the structures and functions of the organism and thereby change traits. (MS-LS3-1)

Variations of inherited traits between parent and offspring arise from genetic differences that result from the subset of chromosomes (and therefore genes) inherited. (MS-LS3-2)

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)

In addition to variations that arise from sexual reproduction, genetic information can be altered because of mutations. Though rare, mutations may result in changes to the structure and function of proteins. Some changes are beneficial, others harmful, and some neutral to the organism. (MS-LS3-1)

 

modeling chromosomal mutations collage


 

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