Punnett squares are commonly used in the study of genetics to predict the outcomes of a genetic cross when considering one or two characteristics. For students with visual impairment, particularly for those who are blind, Punnett squares can be very difficult. This tactile aid should effectively increase the student’s understanding of Punnett squares and his ability to complete them.
- APH Graphic Aid for Mathematics
- 3 flat spring wires (from APH graphic aid kit)
- 7 flat push pins to secure rubber bands and flat spring wires.
- 12 pins of one variety
- 12 more pins of a clearly distinct shape (See picture.)
Note: Pins may be obtained from any office supply store.
- Prepare an APH Graphic Aid by building the axes with either yarn or rubber bands. The pictures shows yarn but rubber bands may be a better choice. The yarn or rubber bands will be held by flat push pins on the top and bottom of the graphing aid in the middle and on the left and right in the middle. (See picture.)
- In order to give the student a clear tactile space to indicate the alleles of each parent, use flat push pins to secure a flat spring wire (from APH graphic Aid ) horizontally 1.5″ below the top of the graph board and another flat spring wire vertically 1.5″ to the right of the left side of the graph board (See picture.)
- Choose 2 clearly distinct types of pins for the student to use as dominant and recessive alleles. The picture indicates white tacks as dominant and spherical blue pins as recessive.
As students are learning to complete Punnett squares, braille students who are struggling to complete them will benefit from this tactile aid. The following detailed description of the picture will precede the procedure.
The pins used in this picture are white flathead push pins to represent the dominant allele and round head pins to represent the recessive allele. The picture shows the cross between a homozygous dominant (2 dominant alleles) and a heterozygous individual (one dominant and one recessive allele). When discussing seed shape (round or wrinkled) this would be written as RR X Rr.
- Describe the location of the alleles from the first parent as above the horizontally placed flat spring wire – one allele should be placed above each of the top 2 quadrants of the graph board in the center . Have the student place the alleles for the first parent in this position.
- Describe the location of the alleles from the second parent as to the left of the vertically positioned flat spring wire. Have the students place the alleles in this position. (See picture.)
3. Assist the student to perform a cross by explaining that each square (quadrant of the graph board) will be filled by combining the allele from the top with the allele from the side. This may require some practice.
4. After the cross is complete, have the student describe the offspring in each box. Ask appropriate questions about the probability of homozygous dominant, homozygous recessive, and heterozygous offspring.
5. After the student feels confident, allow him/her to perform numerous crosses independently.
Demonstration videos for Punnett Square Tactile Graphic Aid
A student from TSBVI explains how to use the Punnett Square Tactile Graphic Aid in the videos below.
- Rubber bands could be used instead of yarn as the X and Y axis
- Yarn or rubber bands could be used in place of the flat spring wires.
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)
This activity was created by Marcus Coldwell and Devin Gutierrez.
Pictures by Ditmar Hospitál
By Laura Hospitál
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