tedarling's blog

We conducted several experiments with Saccharomyces cerevisiae, in order to study the life cycle of yeast, the principles of complementation, and tetrad analysis. The life cycle of yeast can be easily studied at various stages because it reproduces through budding and exhibits predictable morphological changes in this process. Genetic complementation is the reappearance of the wild-type phenotype in offspring when there are two different homozygous recessive mutations present in the parent organisms. Complementation can be easily observed in yeast using the ADE mutations. If the ADE mutations, which inhibit adenine biosynthesis, are on separate genes, then complementation will occur. Complementation in yeast would result in the ability to produce adenine, even though neither of the haploid strains are capable of doing so. Tetrad analysis involves examining the completion of the entire yeast life cycle.

Yeast can reproduce both sexually and asexually. The two mating types of haploid yeast are MATa and MATα. Each mating type produces unique pheromones that facilitate mating by allowing cells to sense nearby mating partners and grow toward them. Each of the haploid mating types are capable of being maintained indefinitely if kept seperate. If the two separate mating types encounter each other they may fuse, and produce a diploid cell through a process called conjugation. Conjugation is the sexual process by which haploid cells of the opposite mating type form a diploid zygote. Once the diploid state is formed, it can also be maintained indefinitely, given sufficient nutrients. If the conditions are not adequate the diploid cell will undergo meiosis, or sporulate, and produce four haploid spores known collectively as an ascus.

Over the course of several weeks we carried out multiple related experiments on Saccharomyces cerevisiae, a species of yeast. Yeast is vital to study because it is the simplest of all the eukaryotes and is the basis of our understanding for numerous essential cellular processes. Yeast is a unicellular, eukaryotic fungus that reproduces through budding. To replicate, a bud emerges from the mother cell during S phase of the cell cycle. The bud grows until it is pinched off with newly replicated DNA inside. Yeast can exist in both haploid and diploid states, and both undergo budding.

We conducted several experiments with Saccharomyces cerevisiae, in order to study the life cycle of yeast, the principles of complementation, and tetrad analysis. The life cycle of yeast can be easily studied at various stages because it reproduces through budding and exhibits predictable morphological changes in this process. Genetic complementation is the reappearance of the wild-type phenotype in offspring when there are two different homozygous recessive mutations present in the parent organisms. Complementation can be easily observed in yeast using the ADE mutations. If the ADE mutations, which inhibit adenine biosynthesis, are on separate genes, then complementation will occur. Complementation in yeast would result in the ability to produce adenine, even though neither of the haploid strains are capable of doing so. Tetrad analysis involves examining the completion of the entire yeast life cycle.

Endler’s hypothesis was correct. Predation heavily influences guppy spot brightness. The

data from the second experiment especially supports this hypothesis. It shows that as predation

increases, spot brightness decreases. Endler’s greenhouse experiments show that without

predation, the spot brightness increases substantially over time. However, in the Cichlid ponds,

the spot brightness decreased substantially over time. The data he obtained from the field are also

consistent with the data form the lab. Finally, the data from the second experiment is very similar

and the same conclusions can be drawn.

Our proposed research question is: How does microinvertebrate soil diversity vary with proximity to trees, water sources, and buildings. Groups will collect soil samples at varying distances from these three variables, then count and identify the species present. Information obtained from the soil samples will help in quantifying species diversity and soil diversity. Species diversity is an indicator of tree and soil sustainability that will provide data for future tree and soil management and be beneficial to the UMASS Amherst campus local climate.

Endler’s hypothesis was correct. Predation heavily influences guppy spot brightness. The
data from the second experiment especially supports this hypothesis. It shows that as predation
increases, spot brightness decreases. Endler’s greenhouse experiments show that without
predation, the spot brightness increases substantially over time. However, in the Cichlid ponds,
the spot brightness decreased substantially over time. The data he obtained from the field are also
consistent with the data form the lab. Finally, the data from the second experiment is very similar
and the same conclusions can be drawn.

The results for experiment 2 were as expected, and strongly support the hypothesis. In the experiment there were 5 various levels of predation tested. All the data show that as predation increases, spot brightness will decrease over time. This is because the guppies with elaborate colors are more apt to attract predators, thus high spot brightness results in a lower fitness. For the first four levels of predation, the spot brightness still increased. However, the net increase became smaller as predation increased. Finally, with enough predators present, the spot brightness decreased. This is likely because the effects of predation on fitness were stronger than those of sexual selection. Without predation, the data show that spot brightness should increase
substantially over time, due to sexual selection. Therefore, the guppies unknowingly play a fitness balancing game between higher predation and more potential mates.

The results for experiment 1 were somewhat surprising. As expected, the data suggest
that different substrates did affect the survival of the guppies. However, one perplexing result is
that the vegetative substrate had the smallest average increase in spot brightness. It seems logical
that the vegetative substrate would provide ample hiding places for guppies, and thus spot
brightness would not be so ill favored due to predation. Additionally, spot brightness increased
substantially in the sandy substrate tank. This seems odd because this environment would not
provide abundant hiding places, unless guppies were to burrow under the sand. Finally, the
muddy tank had the largest increase in spot brightness. This is likely because the mud prevented
predation and allowed spot brightness to increase over time.

The results for experiment 2 were as expected, and strongly support the hypothesis. In the
experiment there were 5 various levels of predation tested. All the data show that as predation
increases, spot brightness will decrease over time. This is because the guppies with elaborate
colors are more apt to attract predators, thus high spot brightness results in a lower fitness. For
the first four levels of predation, the spot brightness still increased. However, the net increase
became smaller as predation increased. Finally, with enough predators present, the spot
brightness decreased. This is likely because the effects of predation on fitness were stronger than
those of sexual selection. Without predation, the data show that spot brightness should increase
substantially over time, due to sexual selection. Therefore, the guppies unknowing play a fitness
balancing game between higher predation and more potential mates.

For experiment 1, the data suggest that the type of substrate did indeed affect survival of
guppies, which altered spot brightness over time. The muddy substrate had the largest average
increase in spot brightness, 3.5. The vegetative substrate had the smallest average increase in
spot brightness, 2.0 and sandy substrate had an increase of 3.0.

For experiment 2, the data suggest that as predation increases, the spot brightness of
guppies decreases over time. For the trial with no predators, there was an average increase in
spot brightness of 7.0. For the highest level of predation, there was an average decrease in spot
brightness of 1.5. All 3 other trials of varying predation levels also support the hypothesis.