Sperm/Egg 23 chromosomes, how many chromatids?

[dentista123]

How many chromatids in a sperm cell with 23 chromosomes?

I know it's basic, I just want to triple check that I understand the whole chromatid/chromosome idea in varying situations.

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[mmorris86]

Nice question, made me learn something 🙂 This explanation is awesome: (under "quantity")

http://en.wikipedia.org/wiki/Chromatid

 

[americanpierg]

Nice question, made me learn something 🙂 This explanation is awesome: (under "quantity")

http://en.wikipedia.org/wiki/Chromatid

The "explanation" under "quantity" just complicates things and makes no sense.

Bascially a chromatid is an arm in a chomosome extending from the centromere. A chromosome can be made up of 1 or 2 chromotids. 1 centromere = 1 chromosome. When it's pulled apart during replication, 1 chromatid can be may still have one centromere, and still be considered one chromosome because there is still one centromere, even though its now just 1 chromotid and not 2.

 

[jay47]

How many chromatids in a sperm cell with 23 chromosomes?

I know it's basic, I just want to triple check that I understand the whole chromatid/chromosome idea in varying situations.

It took me the entire freshman year to figure out what the hell the numbers meant, but I finally got it when I took genetics.

A chromosome can be one of two things:

A. A chromosome with TWO chromatids connected at the centromere (a "duplicated chromosome")

B. A chromosome with ONE chromatid connected by a centromere. (an undiplicated chromosome)

You see, you have to define what a "chromosome" is before you can count them.
Now, let's examine the actual chromosomes in an egg or sperm. They will be n (meaning half the number of normal chromosomes), so 23.

Now, what do those chromosomes look like? Do they have 2 chromatids apiece, or just one?

Take a look here...http://publications.nigms.nih.gov/thenewgenetics/images/ch1_meiosis.jpg

You can see the meiosis I is reductive, that is, the number of chromosomes is halved, and in meiosis II, the number of chromosomes stays the same, but the number of chromatids in each cell is halved.

So each gamete is composed of 23 chromosomes, each with 1 chromatid, for a total of 23 chromatids!

 

[jay47]

The "explanation" under "quantity" just complicates things and makes no sense.

Bascially a chromatid is an arm in a chomosome extending from the centromere. A chromosome can be made up of 1 or 2 chromotids. 1 centromere = 1 chromosome. When it's pulled apart during replication, 1 chromatid can be may still have one centromere, and still be considered one chromosome because there is still one centromere, even though its now just 1 chromotid and not 2.

Agreed, I don't think 4N is a common term, unless you are referring to meitotic defects/nondisjunction stuff. They shouldn't make up a definition of N for chromosomes and chromatids. Your explanation is perfect.

 

[bbwreckerz04]

The chromatid number is double in mitosis for the number of chromosome, in meiosis the number of chromosome is equal to the number of chromatid.

 

[dentista123]

It took me the entire freshman year to figure out what the hell the numbers meant, but I finally got it when I took genetics.

A chromosome can be one of two things:

A. A chromosome with TWO chromatids connected at the centromere (a "duplicated chromosome")

B. A chromosome with ONE chromatid connected by a centromere. (an undiplicated chromosome)

You see, you have to define what a "chromosome" is before you can count them.
Now, let's examine the actual chromosomes in an egg or sperm. They will be n (meaning half the number of normal chromosomes), so 23.

Now, what do those chromosomes look like? Do they have 2 chromatids apiece, or just one?

Take a look here...http://publications.nigms.nih.gov/thenewgenetics/images/ch1_meiosis.jpg

You can see the meiosis I is reductive, that is, the number of chromosomes is halved, and in meiosis II, the number of chromosomes stays the same, but the number of chromatids in each cell is halved.

So each gamete is composed of 23 chromosomes, each with 1 chromatid, for a total of 23 chromatids!

That's kind of what I thought. Thank you!!


Thank you to everyone for your input.

 

[pbure9]

well since we're at this, if i was to really overcomplicate the matter... there would be 46 chromatids in a secondary spermatocyte and double that in a spermatogonium?

figured i'd ask since i was wondering. lol