After the first embryonic division in Parascaris equorum, there is an animal blastomere and a vegetal blastomere, as shown in the figure. The germ plasm is located at the most distal end, positioned away from the animal pole. At the end of the second division, only one of the cells retains the entire genome and becomes a stem cell. This is based on cytosolic factors contained within the germ plasm. The other three cells at this stage show a reduction in chromosome content via a process called chromosome diminution. If an experiment were performed that altered the distribution of the germ plasm in the animal and vegetable poles, what would be the expected result?
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a
No stem cells would be found at the four-cell stage.
b
One stem cell would be found at the four-cell stage.
c
Two stem cells would be found at the four-cell stage.
d
Three stem cells would be found at the four-cell stage.
e
Four stem cells would be found at the four-cell stage.
b
One stem cell would be found at the four-cell stage.
b
One stem cell would be found at the four-cell stage.
To determine the expected result of the experiment that alters the distribution of the germ plasm in the animal and vegetable poles, let's analyze the given information.
In Parascaris equorum, after the first embryonic division, there is an animal blastomere and a vegetal blastomere. The germ plasm, which contains cytosolic factors, is located at the most distal end away from the animal pole. During the second division, only one cell retains the entire genome and becomes a stem cell due to the cytosolic factors contained within the germ plasm. The other three cells undergo chromosome diminution, resulting in a reduction in chromosome content.
Now, if the experiment were to alter the distribution of the germ plasm in the animal and vegetable poles, it would disrupt the normal distribution of the cytosolic factors. Consequently, it would be expected to impact the process of stem cell determination.
Based on the information provided, we can conclude that only one stem cell is formed due to the presence of the cytosolic factors contained within the germ plasm. Therefore, if the distribution of the germ plasm is altered, it is reasonable to assume that the expected result would be the loss or reduction in the number of stem cells produced.
Hence, the correct answer is option a) No stem cells would be found at the four-cell stage.