Science Buddies: "Ask an Expert"

Our science fair project involves exposing Yeast to x-rays and studying the effects on growth rates, mortality rates and mutation of the ADE1 and ADE2 genes. We want to use a standard x-ray machine at a veterinary clinic that we have access to.

My question is, is this machine capable of delivering enough radiation to affect these things? I have found other studies that refer to Kiloroentgens (from 1 - 10 ). How do I figure this out? Can I just zap them multiple times to increase the exposure? How do I calculate it?

The machine is:
Innovet Summit Model HF4
Machine Ranges:
up to 300ma
up to 125 Kvp

Hi,
Yes, Xrays will definitely cause mutations in yeast, and at higher doses will kill the cells by damaging their DNA. Xrays are what is known as ionizing radiation, and the energy they carry can cause actual breaks in the DNA strands. The cells are able to repair a certain amount of this damage but the repair process sometimes makes errors and that’s where the mutations come from. When the radiation is too powerful the DNA undergoes breaks in BOTH strands and this usually kills the cells.

There are several ways to measure Xray dose and I’m sure the machine you will be using has been calibrated and can deliver the required dose. The problem, as you said in your post is figuring out what dose to use. There are several ways to measure radiation. The traditional Geiger counter registers ionizations inside its chamber as an xray or particle passes through. That’s the click you hear. The reading on the dial, however, may not tell you the biological effectiveness of the radiation. Here’s some more information about this: https://www.sciencebuddies.org/science- ... fety.shtml

I suggest that you do a literature search and try to find the dose range for Xrays that causes mutations but does not kill the yeast. I have attached a paper that gives information about survivable doses of Xrays for the yeast, Saccharomyces cerevisiae. You will probably have to do some preliminary experiments to determine the correct dose and dose rate for your particular conditions, but this paper should give you a ballpark idea of the dose rate in rads/sec. You can give a range of doses simply by increasing the time of exposure at a fixed kV and current in milliamps.

Let us know if you have more questions.

Best wishes,

Sybee