The organisms used in this lab are the Ascomycota fungi Sordaria fimicola. S. fimicola is made of haploid cells in a hyphae. A diploid cell is formed when two haploid nuclei bud off of the hyphae. This diploid cell then undergoes meiosis and mitosis forming eight haploid cells called a tetrad. The cells develop within an ascospore, and a group of ascospores is an ascus. An perithecia contains the asci (Glase, 1995).
S. fimicola have a unique feature in their meiotic process which easily lends to figuring out a gene-centromere distance in their chromosomes. During meiosis, the crossing over of genes occurs at any area between the chromosomes. In crossing over, chiasmata occur where parts of the two chromosomes break and reconnect. This creates two separate chromosomes containing pieces of each chromosome which causes gene …show more content…
The eight ascospores are thus arranged in specific order in terms of their phenotype color. The wild type is darkly colored, and the grey mutant is lightly colored. These differences are easily observed in the hybrid. If there is no crossing over in meiosis between the centromere and the ascospore color gene, the sister chromatids will segregate and carry the same allele. This causes the first four ascospores to be the same phenotype and the last four to be the same of the other phenotypes, creating a recombinant 4:4 tetrad. If there is crossing over between the centromere and the ascospore color gene, the chromatids will separate so each has a different allele. This will cause the first and last two ascospores to have different phenotypes. After meiosis II and mitosis, the tetrad will have an unrecombined order in terms of ascospore color including 2:2:2:2, 2:4:2, or any other non 4:4 sequence. This is termed the second division segregation (Glase, 1995). The amount of each in the sample allow for the data to figure out the gene-centromere
S. fimicola have a unique feature in their meiotic process which easily lends to figuring out a gene-centromere distance in their chromosomes. During meiosis, the crossing over of genes occurs at any area between the chromosomes. In crossing over, chiasmata occur where parts of the two chromosomes break and reconnect. This creates two separate chromosomes containing pieces of each chromosome which causes gene …show more content…
The eight ascospores are thus arranged in specific order in terms of their phenotype color. The wild type is darkly colored, and the grey mutant is lightly colored. These differences are easily observed in the hybrid. If there is no crossing over in meiosis between the centromere and the ascospore color gene, the sister chromatids will segregate and carry the same allele. This causes the first four ascospores to be the same phenotype and the last four to be the same of the other phenotypes, creating a recombinant 4:4 tetrad. If there is crossing over between the centromere and the ascospore color gene, the chromatids will separate so each has a different allele. This will cause the first and last two ascospores to have different phenotypes. After meiosis II and mitosis, the tetrad will have an unrecombined order in terms of ascospore color including 2:2:2:2, 2:4:2, or any other non 4:4 sequence. This is termed the second division segregation (Glase, 1995). The amount of each in the sample allow for the data to figure out the gene-centromere