i need an illustration

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nikeman
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i need an illustration

Post by nikeman » Mon Jun 26, 2006 3:33 am

I need an illustration of a sexually reproducing species cell during the life cycle (G1, S, G2, and M phases) with

2n=6 and n=3

My teacher most have forgotten to give it to use because it says refer to the board but she didnt draw anything... I have to fill out a chart using this and my teacher is pretty strict and pretty bad at explaining stuff...

majik1213
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Post by majik1213 » Fri Jun 30, 2006 4:39 pm

The information you have provided is enough for you to draw your own illustration. Here is what I'd do. Please note that this is not sexual reproduction (meiosis), as you hinted in your post, but rather it's cellular growth/replication/division. Also, it's not the life cycle, but just the cell cycle. At least I think.

First note some things about the given information, specifically, 2n=6, or that there are 6 chromosomes. The cell is a diploid, because of the 2 before the n. If the two were a three, then it would be a triploid cell, which rarely exist due to issues involving the odd number of chromosomes. If you were given n=6, then you would have a haploid cell, which cannot exist except as a gamete I think (not sure).

Anyways, your basic cell will have 6 chromosomes then, and they pair up in the sense that 3 of the chromosomes can be colored, oh say red, and the other 3 blue. Then match one red with one blue to show that 2n=6. The red can represent the maternal, and the blue paternal, or vice versa. Now for the phases:

G1 - no chromosomes are formed, only uncondensed heterochromatin exist, which cannot be seen by the naked eye. In contrast, constitutive chromatin cannot decondense, so these regions are visible; however, I doubt your sloppy teach will care, so I'd just note that the chromatin is there, but invisible. G1 is the growth stage

S - this stage is the DNA replication stage; in this diagram you must take each of your 6 chromosomes and duplicate them into what we call sister chromatids. Now you will have what would appear to be 12 chromosomes, but this term would be incorrent. You see, the word chromosome is a tricky word because it refers to different structures at different times. One reason for this wacky convention is to preserve the 2n=6 relation, I guess. At any rate, what you can say is that you had begun with 6 chromatids and 6 chromosomes, and after duplication you ended up with 12 chromatids but still 6 chromosomes, as the word chromosome, after duplication, referred to a sister chromatid pair. Incidentally, chromatids are composed of chromatin. As you may see, there is a lot of nuances that are important in this vocabulary soup. Anyways, such pairs (sister chromatids) did not exist prior to replication. Notice how 2n=6 is maintained.

G2 - a stage where the cell prepares to divide, but I can't say that you would see much change in the chromosomes. Just note that there RNA and protein (especially tubulin for microtubules in eukaryotic cells) are actively synthesized. And perhaps mention that when the level of the mitosis promoting factor (MPF) is sufficiently high, mitosis is triggered.

M - mitotic stage. I have no idea how your teacher wants to split this part up, but you should be able to take it form here. Good luck.

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