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* The Problem
* The Method
* The Investigation
* Personal Investigation page
Research Assistant Wanted

Brother Gregory wants you to help him map the position of genes on yeast chromosomes. In this investigation you will be provided with diploid yeast cells that were made by fusing together different haploid yeast mutants.

You will then sporulate these diploid yeast cells, forcing them to undergo meiosis and producing four, related, haploid yeast cells once again. Since all four "spores" (haploids) stay together in the same ascus, they can be carefully separated out and their growth patterns analyzed.

From your results, you should be able to calculate the distance apart two genes are on the same chromosome, and from these distances you should be able to make a "map" of the relative positions of three genes.

Assistants

You are to become Brother Gregory's research assistant. You must carry out the experiment, gather data, analyze your results and give Brother Gregory the answer you have found.

First, print out your personal investigation page (below) and find out how many genes (steps in a pathway) are in the sets of mutants you are supposed to investigate. Carry out the experiment, gather and record your data, analyze your results and write down the appropriate numbers on your personal investigation page.

This is important. Bring your completed investigation page to the examination, if it is required by your topic schedule.



Page Items
* Research Assistants
* The Method
* The Investigation
* Personal Investigation page
The Problem

Special diploid yeast cells have been prepared for you. They were made by mating together different haploid yeast mutants. You must now use the technique called tetrad analysis to analyze what happens when large numbers of these special diploids undergo meiosis.

You must determine how many times a crossing over event occurs between two genes on the same chromosome takes place as the diploid undergoes meiosis and becomes four haploid yeast cells once more.

From this information, you should be able to work out how far apart two different genes are on the same chromosome.

Biological Information is Linear



Page Items
* Research Assistants
* The Problem
* The Investigation
* Personal Investigation page
The Method

In these investigations you will observe what happens when a large number of diploid yeast cells undergo meiosis and separate out their various chromosomes into different sets of haploid cells.

The number of "crossing over" events that occurs between any two genes is an indication of how far apart they are on the chromosome. Genes that are far apart will have more crossing over events that two genes that are close together.

Before you begin, take this opportunity to read about tetrad analysis, and how you can study the outcomes of individual meiosis events and use this information to construct chromosome maps.

How to carry out tetrad analysis



Page Items
* Research Assistants
* The Problem
* The Method
* Personal Investigation page

Start the Investigation

In this investigation you have been assigned three different genes, all on the same yeast chromosome. You must find out how far apart each pair of genes is on this chromosome, and then use this information to construct a 'chromosome map' that marks the relative position of each gene.

The genes being studied come in two different forms; AAA- the 'normal' gene form and aaa- the mutated gene form. Both can be followed and identified by the way they grow on minimal media and supplemented media.

The diploid- cells are always formed so that the normal AAA gene and the normal BBB gene are on the same chromosome, and the mutant aaa gene and the mutant bbb gene are on the same chromosome.

This is usually written: [AAA/aaa BBB/bbb] for the diploid genotype.

After one of these diploids has undergone meiosis, the ascus contains four, halploid sprores, and the growth characteristics of each spore in the set can be determined by growing colonies of cells on different kinds of selective media.

print out this special form on which to record your tetrad analysis results

You must record how each 'tetrad' grows on different media and determine what type of tetrad it is; PD or NPD or T. A special form has been provided for this purpose. Print it out and use to to keep a track of your results.

You should make sure that you perform this analysis many times (10x ?) for each pair of genes in order to get results that are consistent and have a minimal error factor.

Tetrad analysis

Using the results you have just obtained for each pair of genes, you must now use a special formula to calculate the distance apart each gene is on the chromosome. You can do this using the following calculator:

Calculate the Distance

Finally, using the 'map distance' for each pair of genes, see if you can fit them together in a logical, linear sequence as they would appear on the yeast chromosome.

e.g. ---AAA-----------CCC-----BBB---

Print out your
personal investigation page

Page Items
* Research Assistants
* The Problem
* The Method
* The Investigation
Carefully enter your Seat Number or PCIN number
(e.g.
MM34, or MA56, or WA41)
in the box below, click, and print out the page that appears.

Find the answers to the questions, write your answers on the investigation page, and bring the completed assignment to the designated exam for grading purposes.

Personal Investigation Page

Enter your seat number or PCIN number here: -


Science@a Distance
© 2002, Professor John Blamire