Meiosis and crossing over licorice lab

During meiosis, in the cell, a spindle apparatus forms. One tetrad attaches to the spindle on one side. Other tetrad attaches to spindle on the other side.

Here we don’t want exact copies of the parent – we want all daughter cells to be different! So the chromosomes start crossing over – like shuffling a deck of cards. Here’s a simplified physical representation:

Bits of one chromosome break off and stick on another chromosome, and vice-versa. This process is more or less random – the results are slightly different every time.

After this happens, the mixed up chromosomes are then pulled by the spindle apparatus to opposite sides of the cell (once done, it then divides into two new cells.) We see this here:

From Meiosis video by Raghavendra Rao

Students better understand this when they model this physically! We can use Twizzlers or any other colored licorice.

Here we see chromosome forming a tetrad, before pieces break off and rearrange:

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Here a student shows what happens during the time when pieces of one chromosome break off, and move onto a nearby one.

(For ease of use, the licorice pieces aren’t in a tetrad shape at the moment.)

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and

Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-LS3-1. Develop and use a model to show how DNA in the form of chromosomes is passed from parents to offspring through the processes of meiosis and fertilization in sexual reproduction.

HS-LS3-2. Make and defend a claim based on evidence that genetic variations (alleles) may result from (a) new genetic combinations via the processes of crossing over and random segregation of chromosomes during meiosis, (b) mutations that occur during replication, and/or (c) mutations caused by environmental factors. Recognize that mutations that occur in gametes can be passed to offspring.

Disciplinary Core Idea Progression Matrix – “Nearly every cell in an organism contains an identical set of genetic information on DNA but the genes expressed by cells can differ. In sexual reproduction, genetic material in chromosomes of DNA is passed from parents to offspring during meiosis and fertilization.“

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