A-Level Biology - Meiosis help please

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Anonymous -
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Hiya!

I might be asking a very obvious question, but I am getting very confused and over complicating the process of meiosis...

So on diagrams explaining meiosis, the cell undergoing meiosis contains paternal AND maternal chromosomes? I don't really understand why, as I would have thought that, in females for example, it would only be maternal chromosomes, since eggs are being produced which only contain the maternal DNA?

I have no clue if that makes sense, but I wasn't really sure how to put my thoughts into words.

Also, after DNA replication, before meiosis occurs, would the cell contain the diploid number of chromosomes (23 pairs), or double this?

Again, sorry if those were obvious or silly questions

Thank you in advance for the help
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Octavian1
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hiya,

So to answer your first question we get both sets of chromosomes from our parents, this pair of the same type of chromosome, one from mum and one from dad is called a homologous pair. It doesn't matter if you're a male or female you get half the dna from mum, half from dad.

Regarding the second question: before meiosis the cells are diploid as you get both sets of chromosomes from mum and dad. Now after meiosis, the cells are haploid. With dna replication (interphase) the amount of dna present doubles. But the cells are still diploid- its weird i know! as what has happened is just that the same chromosomes are present but just duplicated.

Look at the image i've attached. We start off with two set of homologous chromsomes (of the same type) before interphase and after interphase they are just duplicated. They are still called chromosomes, each individual chromsome in the duplicated version is called chromatid and this attached at the centromeres.

I hope this is some help. I know this topic is a bit confusing but keep trying to understand it! Take a look at Miss Estruch on youtube, her vids
are pretty good.
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Anonymous -
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(Original post by Octavian1)
hiya,

So to answer your first question we get both sets of chromosomes from our parents, this pair of the same type of chromosome, one from mum and one from dad is called a homologous pair. It doesn't matter if you're a male or female you get half the dna from mum, half from dad.

Regarding the second question: before meiosis the cells are diploid as you get both sets of chromosomes from mum and dad. Now after meiosis, the cells are haploid. With dna replication (interphase) the amount of dna present doubles. But the cells are still diploid- its weird i know! as what has happened is just that the same chromosomes are present but just duplicated.

Look at the image i've attached. We start off with two set of homologous chromsomes (of the same type) before interphase and after interphase they are just duplicated. They are still called chromosomes, each individual chromsome in the duplicated version is called chromatid and this attached at the centromeres.

I hope this is some help. I know this topic is a bit confusing but keep trying to understand it! Take a look at Miss Estruch on youtube, her vids
are pretty good.
Thank you ever so much!!

So meiosis starts off with normal body cells, just like in mitosis? But the difference between mitosis and meiosis I is that in meiosis the chromosomes pair up on the equator, rather than simply line up at the equator? (I don't know if that makes sense)

The main part that confuses me is that I thought that female gametes only contain female genetic material, and male gametes only contain male genetic material - I assume that this is not the case? If this is the case, then is the role of the sperm not to carry male genetic material? (if gametes contain both male and female DNA)

I'm really sorry if I'm still getting this wrong, and thanks again for the help
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Octavian1
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(Original post by Anonymous -)
Thank you ever so much!!

So meiosis starts off with normal body cells, just like in mitosis? But the difference between mitosis and meiosis I is that in meiosis the chromosomes pair up on the equator, rather than simply line up at the equator? (I don't know if that makes sense)

The main part that confuses me is that I thought that female gametes only contain female genetic material, and male gametes only contain male genetic material - I assume that this is not the case? If this is the case, then is the role of the sperm not to carry male genetic material? (if gametes contain both male and female DNA)

I'm really sorry if I'm still getting this wrong, and thanks again for the help
hello,

So the sperm carries genetic info from the male (this male has dna from his mum and dad).
The egg carries genetic info from the female (this female has dna from her mum and dad).

Hence, the gametes contain a mixture of chromsomes from their mum and dad.

In meiosis I, the chromosome pair up on the equator and what happens is independent assortment, where some chromosomes from mum may
be put on the left or right and some chromosomes from dad may be put on the left or right. The order of this is random. The homologous chromosomes (same type: ie chromosome 1 from mum is homologous to chromsome 1 from dad) then form a chiasma where some genetic information is exchanged which introduces genetic variation. Chiasmata is where the chromsomes wrap around each other and some genes are transferred.

Meiosis 1 is unique, while meiosis 2 is similar to mitosis with the only difference being that the cells produced at the end of meiosis are haploid.

Hope this helps! Don't feel embarrassed, please do ask some more questions if you have any. If the explanation for where the genetic material from the gametes comes from does not make sense, please do tell me!
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(Original post by Octavian1)
hello,

So the sperm carries genetic info from the male (this male has dna from his mum and dad).
The egg carries genetic info from the female (this female has dna from her mum and dad).

Hence, the gametes contain a mixture of chromsomes from their mum and dad.

In meiosis I, the chromosome pair up on the equator and what happens is independent assortment, where some chromosomes from mum may
be put on the left or right and some chromosomes from dad may be put on the left or right. The order of this is random. The homologous chromosomes (same type: ie chromosome 1 from mum is homologous to chromsome 1 from dad) then form a chiasma where some genetic information is exchanged which introduces genetic variation. Chiasmata is where the chromsomes wrap around each other and some genes are transferred.

Meiosis 1 is unique, while meiosis 2 is similar to mitosis with the only difference being that the cells produced at the end of meiosis are haploid.

Hope this helps! Don't feel embarrassed, please do ask some more questions if you have any. If the explanation for where the genetic material from the gametes comes from does not make sense, please do tell me!
That makes so much sense, thank you ever so much!!

All of what you've said makes perfect sense, and I really appreciate all of your help
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Octavian1
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(Original post by Anonymous -)
That makes so much sense, thank you ever so much!!

All of what you've said makes perfect sense, and I really appreciate all of your help
i'm glad you understand!
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