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biology question about chromosomes

Genetics as it applies to evolution, molecular biology, and medical aspects.

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biology question about chromosomes

Postby biotchr » Wed Jul 12, 2006 2:36 pm

O.K., I am a biology teacher but I feel like a dummy. I have a question that I know will probably have a very simple answer and make me look foolish as a result. So please try and refrain from criticizing me, although I do have thick skin - after all I do teach high schoolers.

My question surrounds the number of chromosomes inherent within organisms. How can an organism have an odd number of chromosomes? For instance with pea plants they have 7 chromosomes. How do homologous chromosomes line up in meosis I? And what would a karyotype of a pea plant look like? Would there be one chromosome without a partner?

Any help would be greatly appreciated and criticism understandable.
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Postby biotchr » Wed Jul 12, 2006 2:42 pm

Wait a minute - a pea plant has 14 chromosomes. Duh.

But doesnt the odd number still affect the pollen and egg cells when they reproduce?
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Postby biotchr » Wed Jul 12, 2006 2:44 pm

Nope, because originally the specialized cell starts off with a somatic count, right. So to come up with a sex cell you would start with 14, then through the process of meosis I and meosis II, the number is reduced to 7.
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Postby biotchr » Wed Jul 12, 2006 2:45 pm

I think I answered my own question. Anything else I've missed?
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Postby biotchr » Wed Jul 12, 2006 2:45 pm

And is it possible for an organism to have an odd number of chromosomes?
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Postby canalon » Wed Jul 12, 2006 4:54 pm

Yep you pretty much made questions and answers. And rightly so.

As for the odd number of chromosome, you find it in all prokaryotes. It is usually one, but some bacteria have more than one.
Patrick

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Postby biotchr » Thu Jul 13, 2006 4:53 am

Canalon wrote:Yep you pretty much made questions and answers. And rightly so.

As for the odd number of chromosome, you find it in all prokaryotes. It is usually one, but some bacteria have more than one.


Thanks.

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Postby Jelanen » Tue Jul 18, 2006 10:05 pm

Some organisms use the presence or lack of a chromosome to determine sex. I'm sitting at work apart from my texts (and I don't deal with this stuff on a daily basis anymore *sigh*) but I seem to recall drosophila determine sex this way...someone correct me or something here...
'It is futile to pretend to the public that we understand how an amoeba evolved into a man, when we cannot tell our students how a human egg produces a skin cell or a brain cell!'

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Postby xand_3r » Wed Jul 19, 2006 11:06 am

Yes, there are organisms that have an odd number of chromosomes but they can't reproduce. For example some type of roses - that's why gardners are using asexual ways of reproduction for roses. The phenomenon is called polyploidia - meaning 2 or more sets of chromosomes (like 2n, 3n, etc. n= no of chromosomes in a haploid cell like a sex cell), and it occurs as an adaptation to harsh conditions (polyploids are more resistant, they grow taller, etc.; natural polyploids usually have 4n, 8n etc. chromosomes so they can reproduce. Hybrids between different polyploids might produce polyploids with odd number of chromosomes. Polyploidia in the animal regnum is unlikely to happen, being lethal.
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Postby chloe18 » Fri Jul 21, 2006 6:53 am

I think it's a result of autopolyploidy.
You can read about that and then you'll get the answer
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