Tag: Genetics

Sister Chromatids and Non-sister Chromatids – What is the Difference?

It is one of those posts where we clarify doubts between confusing terms. I am talking about sister chromatids and non-sister chromatids. When a cell undergoes cell division, newly produced daughter cells should get the copies of complete set of chromosomes. For this purpose, all the chromosomes undergo replication and produce its identical copy.

• Sister Chromatids –

When chromosomes are replicated they are attached at the centromere before these replicated copies are separated. So these identical copies of chromosome are called sister chromatids. They are called sister chromatids because all the genes and to be specific all the alleles are exactly the same because they are identical copies  (Figure 1).

Sister Chromatids = Replicated Chromosomes Attached at the Centromere.

Figure 1. Sister Chromatids

• Non-sister Chromatids –

We are diploid organisms which means for each pair of chromosome we have one chromosome coming from mother and one chromosome coming from father. Therefore we have homologous pairs for every chromosome.

Figure 2. Non-sister Chromatids

Let’s take figure 2 in consideration and let’s say it is chromosome 1. So it will have its homologous pair and that homologous chromosome also replicates. This would be true for every homologous pair. For this homologous chromosome all the genes are same but alleles might be different (because one has come from mother and one has come from father). Therefore in a homologous pair, the chromosome copies are not identical, isn’t it? Even though the genes are same but the alleles might be different. And because these copies are not exactly the same they are called non-sister chromatids.

Non-sister Chromatids = Replicated Chromosomes of Homologous Pair. 

I hope this post was helpful 🙂

Watch a video on this topic here.