[问答题]
Mitochondria are resp
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ac,dxq 0rw;d*oefz2 3supplying metabolic energy in eukaryotic cells. In most eukaryotes, which reproduce by sexual reproduction, mitochondrial DNA (mtDNA) is inherited from only one of the parents: the mother in the case of humans. This is in contrast to nuclear DNA which is inherited from both parents. It has been suggested that, in some eukaryotic organisms, inheritance patterns of mtDNA found in hybrid cells, which are the result of sexual reproduc
xc*r edwd 3q0f2a;zo,tion between two different yeast species, could be influenced by the parent’s genetic background.
In an experiment, scientists investigated if environmental factors could influence the inheritance of mtDNA in hybrid cells resulting from the sexual reproduction between two closely related species S. cerevisiae and S. paradoxus.
The first step in the experiment was to produce hybrid cells, which were then grown on different agar plates, each providing different growing conditions, which simulated different environmental stresses. Cultures were then taken from each agar plate and grown in a liquid medium, with the same respective environmental conditions. The procedure is outlined in the diagram below.
The mtDNA genotypes of the resulting hybrid cells were then identified and compared to that of the original parents.
1.Describe how the pattern of inheritance of mtDNA in the hybrid cells is affected by the different conditions.
2.Identify the liquid medium which resulted in the greatest AND smallest difference in number between hybrid cells with mtDNA from S.cerevisiae W303 and S paradoxus YDG197.
3.Calculate, for the 2% glucose condition, the percentage of hybrid cells which contained mtDNA genotypes of both S. cerevisiae and S. paradoxus.
4.Compare and contrast the results from the first and second experiments for the 2% glucose condition.
5.Identify the liquid medium condition which resulted in the greatest difference in the number of hybrid cells with mtDNA genotype from both parents between experiments 1 and 2.
In a final experiment, the team of scientists wanted to examine the activity of mitochondria, as indicated by respiratory competency, in the hybrid cells grown under each of the aforementioned growing conditions.
Respiratory competence was measured by using a stain, which stains respiratory competent cells red. The absorbance of cells was then measured, with higher absorbances indicating higher levels of respiratory competency.
Note that hybrid cells which contained both parents' mtDNA were excluded from this experiment.
6.State the growing condition and strain which resulted in the highest levels of mitochondrial activity.
7.Discuss the hypothesis that hybrid cells inherit the mtDNA from parents who are best adapted to their environment.
8.Evaluate the use of S. cerevisiae and related strains in the study of mtDNA inheritance in humans.
