Briefly explain why sister chromatids remain together in...

Key Concepts

Sister Chromatid Cohesion

Sister chromatids are held together by protein complexes (cohesins) along their length. During Meiosis I, although cohesin is cleaved along the arms of the chromosomes to allow the separation of homologs, cohesin at the centromeric region remains intact, ensuring that sister chromatids stay connected.

Cohesin Protection Mechanism

Proteins such as shugoshin protect the centromeric cohesin complex during Meiosis I, preventing its cleavage by separase. This protection is lifted in Meiosis II, where separase targets the centromeric cohesin, allowing the sister chromatids to finally separate.

Meiosis Phases

Meiosis involves two sequential divisions. In Meiosis I, homologous chromosomes are separated (reductional division), while in Meiosis II, the sister chromatids are separated (equational division). The distinct separation events in these phases ensure that gametes receive the correct number of chromosomes.

Transcript

00:01 Here we're being asked for the sort of difference between anaphase 1 and anaphase 2 in myosis.

00:08 So we have anaphase 1 and 2.

00:16 And we're paying attention, of course, to the chromosomes.

00:20 So in anaphase 1, so anaphase 1, the sister chromatids stay together.

00:34 And the reason they stay together is because, because what's happening in anaphase one is that the homologous chromosomes are being separated, not chromatids.

00:45 So we separate the homologous chromosomes.

00:50 Remember, homologous chromosomes are ones that have the same genes on them.

00:55 So you have two copies of chromosome number seven.

00:59 Each of those chromosomes has the same genes on them.

01:03 Now, they may have different alleles for those genes, but they have the same genes on.

01:08 So during, and a phase one, we separate homologous chromosomes.

01:14 So let's just take a quick drawing of it.

01:16 I'm just going to draw three chromosomes.

01:21 I will use blue as my alternate color.

01:24 So remember that they are going to, they're not very well lined up here, are they? imagine they're lined up better than this.

01:35 These are homologous chromosomes, right? each of these, black blue, blue, black, black blue, so each of those is two copies of the same chromosome.

01:45 And they're homologous again because they have the same genes on them.

01:49 What happens in anaphase 1 of myosis is that the two chromosomes are going to be pulled apart, right? and we're going to end up with that one going in that direction and this one pulling in this direction...

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