Lab Report Yeast Mating

Yeast Mating Report

I. Introduction

Before the data and results can be discussed, it is important to understand a few key concepts such as the yeast life cycle, the different mating types a and alpha, and the yeast strains used in the experiment. The yeast life cycle consists of five stages; resting, budding, shmoo, spore and zygote. During the resting stage, or interphase, the yeast haploid cells are not replicating but are taking in nutrients (Urry et al 2014.) Next comes the budding stage in which the haploid cells begin to replicate either by proliferation or sporulation if the haploid cell is in the presence of another cell of the opposite mating type, either a or alpha (explained in more detail later.) In the case of this experiment

The purpose of these different types are to control how likely yeast cells are to mate. A or aa diploid cells mate fairly easily with alpha or alpha diploid cells. When this happens, a heterozygous diploid is the product. This diploid is unable to mate with either a or alpha mating types, but it is able to sporulate, something the haploids cannot do. The cause of this pickiness is the strain 's ability to produce and respond to extracellular signals. For example alpha cells excrete a oligopeptide pheromone “alpha factor” which causes cells to stop in the cell cycle just before the start of DNA replication (Hicks 1973). Yeast cells can also switch between mating types during the growth of a clone of homothallic cells, This process follows several rules, firstly being that when the cell splits, it produces two cells of either the same type as the mother cell, or two cells of the opposite type. Second, the ability to make cells of different mating types is restricted to “experienced cells” or cells that have split before. This means that spores or buds rarely if ever produce cells of a different mating type. There are several different types of strains of yeast each with unique phenotypes and dominance. First there is the a1R strain which is of the white phenotype and dominant. Then there is a2r which has a red phenotype and is of the recessive category. Alpha1R is once again white and dominant while alpha2r is more orangeish

While it was difficult to tell at the time of the mixing, the yeast were not fully mated. Because of this, the alR alpha2r and a2r alpha1R genotypes appeared slighly pink instead of completely white due to the fact that some of the red phenotyped yeast did not mate and grew mitotically (Fig. 3b.)

VI. References

Herskowitz, I. (1988). Life cycle of the budding yeast Saccharomyces cerevisiae. Microbiological Reviews, 52(4), 536–553.

Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2014).Campbell Biology in Focus (Custom Edition for Drexel University). Boston: Pearson.

Hicks, James B., and Ira Herskowitz. "INTERCONVERSION OF YEAST MATING TYPES I. DIRECT OBSERVATIONS OF THE ACTION OF THE HOMOTHALLISM (HO) GENE." MANNEY 1974a,b). In Particular, a Cells (but Not a or A/a Cells Excrete an Oligo- (n.d.): n. pag.Genetics.com. Institute of Molecular Biology and Department of Biology, University of Oregon. Web. 1 Feb. 1973.

Strathern, Jeffrey N., Jones, Elizabeth W., and Broach, James R. (1981). Molecular biology of the yeast saccharomyces, life cycle and inheritance. National Agricultural