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Activity Student Handout This document is made available by the Howard Hughes Medical Institute. Using this document, you agree to use this document in accordance with the Terms of Use INTRODUCTION Scientists have determined the complete DNA sequences of the genomes for many organisms, including humans. By analyzing patterns in those sequences, they can estimate how many genes an organism has - humans, for example, have about 20,000. But sequence patterns alone don't specifically show what each gene does. How can we figure this out? In this activity, you will explore a tool that can be used to determine a gene's function. You will then design your own version of this tool to examine genes that affect the colors and patterns on butterfly wings, PART 1: Using CRISPR-Cas9 to inactivate Genes One way to determine a gene's function is to inactivate, or "knock out," that gene and then observe the effect on a cell or organism. Scientists can inactivate genes in cells growing in a lab or in model organisms, such as files or mice 1. With a partner, discuss what it means to inactivate a gene and how it could be done. Record your ideas. 2. Can you think of additional ways to find out what genes do? Record one or two ideas.

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1. Gene inactivation is a method to artificially stop the function of the gene in order to know the function of the gene. The gene inactivation method are knock -out through insetional mutagenesis. The other method include incorporation of DNA that need to be silenced in the form of hetrochromatin.

2. The other ideas of gene inactivation could be RNA interference where formation of mRNA is inhibited and also downregulating the gene expression in both plants and animals.