Yeast is a unicellular organism that belongs to the fungi kingdom. This mighty yeast is also referred to as the Baker's yeast. It is also scientifically referred to as Saccharomyces cerevisiae. It is a simple yet very beneficial organism that has been used by humans for about 10,000 years. It can either grow through aerobic respiration or anaerobic fermentation hence the production of ethanol and carbon (IV) Oxide. The products of fermentation are very useful in bread making and beer manufacturing industries. Furthermore, this baker's yeast has contributed significantly to human technology. Yeast has a unique ability to reproduce both sexually by meiosis and asexually through mitosis. The type of reproduction it uses is dependent on the environment it is found.
Task 1
Meiosis is the process through which gametes are produced in various organisms. The genetic variation that is observed in organisms also results from two mechanisms that occur at different phases of meiosis. These mechanisms are crossing over and independent assortment. Crossing over happens during the first phase referred to as prophase I in meiosis I. This is the mechanism by which genetic materials are exchanged between two chromosomes that are homologous (Boynton & Greig, 2014). It is usually initiated by a protein referred to as Spo 11. Crossing over results to genetic recombination.
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Independent assortment involves the alignment of homologous chromosomes along the metaphase plate (Boynton & Greig, 2014). It occurs during metaphase I and results in variation due to the random separation of the homologous chromosomes.
When a yeast cell that is diploid and has a dominant mutation that is heterozygous mates with a cell that is homozygous for normal recessive allele; fifty percent of the offspring they produce will have the dominant mutation while the other fifty percent will be carriers.
Task 2
Sexual reproduction is advantageous in an environment that imposes natural selection. One advantage is that it ensures the constant reproduction of organisms that are unique. This is very beneficial in an environment that is changing as it increases the probability of some organisms having characteristics or features that will help them to adapt and survive to the new conditions in the environment (Goodenough & Heitman, 2014)). The other advantage is that it increases genetic variation in organisms. More genetic variation gives the organisms a long-term benefit of being to survive in adverse conditions hence strong natural selection (Darwesh, 2015). Generally, the evolution rate of a population increases due to high genetic variation.
Task 3
As shown the "Simplified Model of Yeast Production" you can tell if a yeast cell is going through meiosis or mitosis in various ways. If a cell is going through mitosis it will produce a diploid cell as shown in the diagram while when it was going through meiosis, it will produce haploid cells. A diploid cell contains has two complete sets of chromosomes (2n) while a haploid cell has one set of chromosomes (n).
Task 4
Some stressors occur more frequently than others. In my experiment, I will use two varying environmental conditions that are based on different stressors. These conditions are oxidative stress that is caused by hydrogen peroxide (Bonner, 2015) and salt stress that results from sodium chloride (Darwesh, 2013).
Task 5
The effect of excess salt on an organism is determined by the ability of the organism to cope with salt that tries to draw water from it. Therefore, in my experiment, I will investigate how sodium chloride is likely to slow sexual reproduction in baker’s yeast.
Task 6
H1: When yeast is exposed to excess salt the rate of sexual reproduction is reduced
Task 7
In my experiment, I will use three populations of yeast and expose them to an environment that is characterized by varying concentrations of sodium chloride. In my research I will expose the yeast to salt stress of 0.2M NaCl, followed by 0.5M. Then in my control experiment, I will expose I will expose the yeast to an environment that is free of sodium chloride. This is the methodology to follow while experimenting.
The independent variable I will use is the varying concentrations of Sodium Chloride while the dependent variable is the rate of sexual reproduction in yeast. The standardized variables in my experiment were sugar content, dissolved oxygen content, PH and temperature.
To ensure that my results are reliable, I will use five replicates or yeast species for each of the sodium chloride concentration. I will use the same replicates for the control experiment.
The materials to use in my experiment are sodium chloride whose concentration will vary depending on the operation, three populations of yeast each with four replicates and test tubes.
Task 8
There was no sexual reproduction when the Sodium chloride was highly concentrated, but reproduction occurred at a slower rate when the sodium chloride was diluted. However, the rate of reproduction was not affected at all when the environment was free of sodium chloride. The reproduction slowed or stopped when the yeast is exposed to an environment that sodium chloride. This is because it draws water from the cell. Water is a crucial requirement for various cellular activities in the cell. Therefore, when these cellular activities are altered sexual reproduction slows or does not occur at. Some of these cellular activities are responsible for the formation of organelles that are necessary for sexual reproduction in yeast. However, in case I did not standardize other factors like nutrient and dissolved oxygen content, the reproduction may not have been affected by sodium chloride.
Task 9
The response of yeast to stress is mainly characterized by the transcriptome and molecular level of the yeast. Suppose a new species of yeast was discovered, these two features would help the yeast to develop some evolutionary and physiological response to salt stress. This yeast could have higher and more effective pathways that could help it to cope with salt stress in a better way compared to their ancestor. This is because it is likely to have a more complex molecular level. I evolved the three generations of this yeast, and it appeared that the rate of sexual reproduction was not affected by the salt stress. The yeast had stress-response genes that helped to mediate the salt stress. The fitness of the yeast was increased compared to that of the ancestral yeast. The rate of reproduction, cell division, and viability of the new yeast was not affected by the salt stress. Therefore, in the future, it is good to use the new species of yeast rather than the old ones for any experiments. The complexity of the structure of yeast makes it more effective in various industries. These industries include the brewing and bread making industries. It is also very effective in cell biology studies.
References
Boynton, P. J., & Greig, D. (2014). The ecology and evolution of non‐domesticated Saccharomyces species. Yeast, 31(12), 449-462.
Bonner, J. T. (2015). Size and cycle: an essay on the structure of biology (Vol. 2087). Princeton University Press.
Darwesh, R. S. (2013). Improving growth of date palm plantlets grown under salt stress with yeast and amino acids applications. Annals of Agricultural Sciences, 58(2), 247-256.
Goodenough, U., & Heitman, J. (2014). Origins of eukaryotic sexual reproduction. Cold Spring Harbor perspectives in biology, 6(3), a016154.
