Casey Taub
3/5/09
Meghan Sherman and Ted Kunkel
Sordaria and linkage
Introduction:
The purpose of this experiment was to describe the procedure for mating different strains
of Sordaria, recognize types of asci that result from these crosses, and discuss the
relationship between the map distance and recombination frequency.
Materials and Methods
Sordaria cultures and culture media in Petri dishes
Compound microscopes
Slides, cover slips, dissecting needles
70% alcohol in small bottles
1.
2.
3.
4.
Took sample plates of wild type and mutant tan of Sordaria.
Took one by one squares of each and placed them on a new plate face down.
Let them sit for a week to grow.
Took samples of Sordaria from where crossing over could have occurred on the
plate and analyzed them on wet mount.
5. Hit wet mount to cause spores to break.
6. Look for ascus that showed that crossing over occurred.
7. Upon finding ones that did, counted how many occurred in meiosis I and how
many occurred in meiosis II.
Results:
Strains
Crossed
(g) x (+)
No. of MI
Asci (4:4)
19
No. of MII
Asci (2:4:2
or 2:2:2:2)
36
Total Asci
% MII
Map Units
55
65%
32.5
The arrangement of the asci all came out from the center into arrangements of the ascus.
There was no order as to where you would find meiosis I or meiosis II crossover asci.
There were double the amounts of meiosis II crossovers to meiosis I crossovers. There
was no evidence of any atypical segregation patterns. Without class data, there would be
no way to find the distance between the two genes. The distance from the gene to the
centromere is the nonparents plus half of the tetrads all divided by the total number of
tetrads. This number would be 19 + .5(36) / 36 = 1.03.
Discussion/Conclusions:
The genetic distance of the map units was 32.5 centiMorgans. Based on our data, the
amount of meiosis II crossovers is about double the amount of meiosis I crossovers.
When looking for any evidence of gene conversion, we were unable to find
recombination of one allele being converted into another allele because we were able to
see both alleles. We saw both light and dark ascospores. The distance from the gene to
the centromere was calculated to be 1.03. Sordaria are appropriate for studying genecentromere distance instead of Drosophila since with Sordaria you can figure out which
meiosis division crossing over occurred since map units are based on frequency of
crossing over; this then makes it easier to calculate the map units based off of data.
I have neither given nor received unauthorized aid on this piece of work, nor have I
knowingly tolerated any violation of the Honor Code. _______________________