Introduction
In this lab the spores of the Sordaria fimicola, a fungus, is examined after meiosis and mitosis. During meiosis, there is always crossing over of genes between the chromosomes, allowing for genetic variation. The eight ascospores contained within an ascus are examined under a microscope and their order determined. The determination of their pattern depends on whether or not there was crossing over – if there was, they are in a 2:2:2:2 or 2:4:2 pattern, and if not, they are in a 4:4 pattern. The frequency of crossing over can be used to determine the distance between the locus of the gene in question and the centromere. The mutant Sordaria fimicola fungus produces a tan hyphae that has tan spores and the wild Sordaria fimicola produces a black hyphae that has black spores. The Sordaria lab is a good example to show the process of meiosis, a type of cell division that reduces the parent diploid cells (2N) to four haploid daughter cells (1N) and also shows the genetic variation that happens as a result of crossing over and independent assortment during meiosis I.
The Evolution Canyon has two slopes. One is the North Facing Slope that experiences a temperate climate while the South Facing Slope experiences a harsher climate. The Evolution canyon for S. fimicola shows that the crossover frequency in South Facing Slope (SFS) is higher than the crossover frequency of the North Slope (NFS) and baseline example of how the gray and tan Sordaria reproduce in optimal conditions was needed in order to find out if they deviated from those results derived when subjected to extreme weather conditions.Therefore the hypothesis for this lab is that difference in recombination frequencies are dependent on their conditions so predictions for this lab will be that recombination frequency will be the same under optimal conditions. Sordaria fimicola are model organisms because they are inexpensive, ethical, easy to see and quick to reproduce.
Some research questions for this experiment are:
a.i. Does crossing-over occur between the spore color gene and the centromere?
a.ii. What is the overall crossover frequency between the spore color gene and the centromere in organisms grown under standard laboratory growth conditions?
a.iii. What is the calculated map distance between the spore color gene and the centromere?
The procedure involves dividing an agar plate into four parts and placing two pieces of wild S. fimicolastrains with two pieces of tan S. fimicola strains. The agar was placed in an incubator at room temperature and allowed to reproduce and recombine with the color beside it. Squashes were obtained by gathering some of the recombinant asci in the agar plate and the data was used to determine the cross over frequencies.
Methods
In this lab, we placed two pieces of the dark wild portions of Sordaria with two pieces of the tan mutant Sordaria. Then, the samples were left incubated and left to reproduce for a few days. The glass slide was cleaned and a drop of water placed on it.
The ascus were slightly scraped with a hook and placed on the glass slide.
The plastic square was then placed over it and with the tip of a pencil the spores were squashed open.
The ascospores were examined through a microscope on a magnification of 400x
The data was recorded
How cross over frequency is calculated (ratio)
Recombinant asci/ total asci
(*for percentage multiply by 100)
Map distance calculation
Cross over frequency percentage divided by 2
Results
Table 1: individual data
Non- recombinant # of type A asci(4:4)
Recombinant
# of type B asci (2:4:2)
Recombinant
# of type C asci (2:2:2:2)
Total
# of asci Total # of recombinant asci ( B+C)
10
3
7
20
10
In table 1, it shows the number of asci observed individually. Out of all twenty asci that were observed, ten of them were recombinant. The other ten were produced without crossing over
