Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: chickadeee on 13/03/2003 13:13:39
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Hello was wondering if you could help been trying to find five similarities and five differences between meiosis and mitosis. I started off really well but now i seem tobe coming up with things likethey both have seven leters and start with 'M'. Help me please its probably really obvious.
Chickadeee[:I]
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:-D I remember having to do the same thing for school ^_^ I got 98% on my test ;-)
Differences:
In meiosis you get four cells from one
In mitosis you get two cells from one
In meiosis the genetic information has changed
In mitosis it's exactly the same
Meiosis is used to make germ cells
Mitosis is used for every other cell in the body
ummm ... I can't think of any more :-p maybe that the stages are called different names or something ... someone else can say something about the similarities ^_^
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There are lots more including :
Meiosis - Chiasmata / Crossing over to exchange corresponding segments of chromosomes
Mitosis - no chiasmata formation
Meiosis - haploid number on completion
Mitosis - diploid on completion
chris
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4 stages of mitosis:
Prophase
Metaphase
Anaphase
Telophase
Meosis undergoes second cell division to produce 4 haploid cells. Don't know whether there's a special name for the stages in meiosis because I haven't study it in details yet.
AG
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in metaphase of mitosis homologous Xsomes line up along the equator, and then in anaphase split into two identical Xtids, and are pulled to opposing poles of the cell by spindle fibres.
In metaphase of meiosis I, homologous Xsomes line up along the equator in a different way, such that both the Xtids of the Xsome are pulled to opposing poles by spindle fibres, thus the resulting cell after telophase I has a haploid number of Xsomes, and each consists of 2 chromatids. (Which may in fact not be identical due to crossing-over.)
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In female meiosis (oogenesis s. ovogenesis), there are two different types of cells to be created, 1 oocytus and 3 polocyti.
Oocytus is large cell with function in reproduction.
Polocytus is small and useless.
In mitosis, doughter cells are identical.
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lol thats a novel way to put it. In my text book the "polocytus" is called a "polar body."
In male spermatogenesis, the primary spermatocyte produces 4 spermatozoa.
In females, the primary oocyte produces only 1 egg. this is because the other cells apparantly don't get as much cytoplasm, and thus die? i am not too sure.
any way the polar bodies are formed at meiosis I and II of oocyte production, and not always will the secondary polar bodies form (from meiosis II)
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Eggs (oocytes) don't actually complete their second meiotic division until they are fertilised.
Also, in relation to a point raised above, after meiosis I the chromosome number is not haploid as stated. The number of chromosomes is halved, yet they exist as duplicated pairs of chromatids (which, as is correctly highlighted, may differ owing to crossing over).
Therefore the actual number of chromosomes is still 46 (2 x 23) i.e. not haploid (23), which isn't achieved until after the final division in meiosis 2.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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quote:
Originally posted by chris
Also, in relation to a point raised above, after meiosis I the chromosome number is not haploid as stated. The number of chromosomes is halved, yet they exist as duplicated pairs of chromatids (which, as is correctly highlighted, may differ owing to crossing over).
Therefore the actual number of chromosomes is still 46 (2 x 23) i.e. not haploid (23), which isn't achieved until after the final division in meiosis 2.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
I disagree. After meiosis I number of chromosomes is 23, i.e. haploid.
Each chromosome has two chromatids, so there are 46 chromatids and 23 chromosomes.
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He's got ya there Chris.
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Chris said after MEIOSIS 1 which is basically like mitosis, and there are some overlapping of chromosomes. It is not halved first then divide by mitosis to create a copy.
It is when is MEIOSIS 2 where amount of DNA materialis not replicated and result in chromosome number being halved. In that case 4 cells can be produced like male gametes.
Special cases in human female gametes where only one egg cel is produced; the other 3 dies. This way all or most of the cytoplasm will go to that one egg cell, which then provide more chance for the fertilsed egg to develop.
Tom
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lets get this sorted:
mitosis --> 2N (diploid)
meiosis I --> N (haploid)
meiosis II --> N (haploid)
You are confused because each chromosome in the cell after meiosis consists of two chromatids like I originally stated. These chromatids separate in anaphase of meiosis 2. The actual number of chromosomes after meiosis I is 23, which is haploid. You even stated that yourself, Chris.
Anyway this is all excellent revision for me for my exams coming up. haha.
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sorry to sorta go off topic, I have got a burning question straight from a past exam paper:
TRUE/FALSE:
Cells entering metaphase of meiosis I contains 4 times the DNA content of a gamete.
I am thinking true, as the cell has 92 chromatids, and the gamete has 23 chromatids. anyone agree?
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I agree.
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quote:
Originally posted by alastair84
sorry to sorta go off topic, I have got a burning question straight from a past exam paper:
TRUE/FALSE:
Cells entering metaphase of meiosis I contains 4 times the DNA content of a gamete.
I am thinking true, as the cell has 92 chromatids, and the gamete has 23 chromatids. anyone agree?
I would say true on this one unless I'm totally missing someting obvoius (which i often tend to do on exam questions)
As for the diploid/haploid thing it IS kind of confusing, but Chris is correct.
That's no moon.... its a GRAPEFRUIT!!!!
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Thank you for critically commenting on my previous post regarding haploidy.
Haploid indeed refers to the number of chromosomes in a gamete. However, the point I was trying to convey (clearly not very well) is that if a cell at the end of meiosis 1 were magically fertilised, despite being 'haploid', it would end up with 3 copies of each gene rather than the normal 2.
Therefore the term haploid could lead to misinterpretation or confusion on the part of other readers because the 'haploid' cell produced by meiosis 1 is clearly different to the haploid cell produced from meiosis 2. Most people reserve the term 'haploid' to refer to the mature gamete.
However, it would appear that my eagerness to avoid causing confusion has backfired. Sorry about that !
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx