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.