What is the difference between Chromosomes/Chromatids etc? Watch

user10101
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I am currently doing A Level Biology revision about Meiosis..

What are the links/differences between Chromosomes/(Sister) Chromatids/Chromatin etc?
Like, how do they all link together in meiosis?

I have looked on wikipedia etc but haven't found it that helpful, and it's not well explained in our books either.

Would be grateful for any help!
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LemonPi
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A chromosome is made up of two chromatids which are joined by the centromere. The chromatids separate from each other during mitosis to form two new chromosomes. The DNA making up a chromosome is dispersed as chromatin.
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user10101
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That makes loads more sense, thank you! How about sister chromatids, where do they come into it?

Also before meiosis I have read that there are 4 (not two) copies of each chromosome.. Does that mean there are now 2 XX shapes or 4?
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LemonPi
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(Original post by user10101)
That makes loads more sense, thank you! How about sister chromatids, where do they come into it?

Also before meiosis I have read that there are 4 (not two) copies of each chromosome.. Does that mean there are now 2 XX shapes or 4?
Replication of DNA happens during interphase. When it's time to divide, the chromatin (dispersed DNA) condenses into chromosomes (X). You have two sets of homologous chromosomes (one from father, one from mother, originally). Each of these chromosomes is made from two chromatids which are exactly the same, hence 'sister' chromatids (one was replicated from the other).

In the first stage of meiosis, the paired up chromosomes line up (XX), and each get pulled into a different cell (one X goes one way, the other X goes another). Then the next divisions are just like mitosis- each X gets pulled into two chromatids. Only from then on they're referred to as chromosomes. It's quite confusing with all these similar words; I hope this is understandable!
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hassam420
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see attachment....hope it helps
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sicarius1992
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The terminology can be confusing for someone new to the topic.

A chromatid is technically a chromosome, look at this image:



Sister chromatids are copies of each other.

In the top image say these two both represent Chromosome 1. Every human has a pair of each chromosome, one from the mother the other from the father.

Before mitosis/meiosis these replicate and form a replicated chromosome:



This contains two chromosomes, which are pulled apart in mitosis.

In meiosis two homologous chromosome form a pair like this:



There are 4 chromosomes in the pairing of the homologous (mitotic) chromosomes. 2 orange, 2 purple.

These then have the potential to exchange DNA segments which is one of the causes variation.

An overall summary of meiosis:



The starting cell has 2 chromosomes and is the starting diploid cell. At the end of meiosis 4 daughter haploid cells are produced. Each containing 1 chromosome.

I hope that helps! It's confusing since the seperate chromatids are chromosomes but the the conventional 'chromosome' is also called a chromosome.
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sicarius1992
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And for your question about chromatin. It is made of genetic material and proteins and is what is normally in the nucleus. This condenses into chromosomes when the cell is about to divide.
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Suman9304036533
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The thin fibre inside the nucleus before cell division is known as chromatin ( fibre ). These fibres,on cell division condense(coils and supercoils) to form thick,short structures called chromosomes. The thick parts on either side of centromere(point of attachment of sister chromatid) is chromatid.
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