Difference Between Sister and Nonsister Chromatids

The key difference between sister and nonsister chromatids is that sister chromatids are identical and contain the same allele in the same loci while nonsister chromatids are not identical and contain different alleles of the same gene in the same loci.

The two types of chromatids found in the cell that undergo cell division are sister chromatids and nonsister chromatids. Generally, chromatids form during early stages of cell division. On the other hand, nonsister chromatids form during metaphase I of meiosis. They are present in the homologous chromosome pair on the cell equator while sister chromatids are present in the same chromosome. Moreover, the centromere of the chromosome joins the two sister chromatids together.

1. Overview and Key Difference
2. What are Sister Chromatids
3. What are Nonsister Chromatids
4. Similarities Between Sister and Nonsister Chromatids
5. Side by Side Comparison – Sister vs Nonsister Chromatids in Tabular Form
6. Summary

What are Sister Chromatids?

Sister chromatids are two replicated chromatids of a chromosome joined together by a centromere. Sister chromatids replicate at S phase of the interphase during the DNA replication. Significantly, both sister chromatids contain the same allele in the same loci. Moreover, sister chromatids of the same chromosome behave differently in mitosis and meiosis.

During the metaphase of mitosis, individual chromosomes align at the cell equator in a way that two sister chromatids distribute besides the metaphase plate or equator. Afterwards, the centromere splits and the two sister chromatids separate from each other and move apart during anaphase. Consequently, the separated sister chromatids move to opposite poles.

Difference Between Sister and Nonsister Chromatids

Figure 01: Sister Chromatids

Moreover, during the metaphase I of meiosis I, homologous chromosomes pairs align at the cell equator. Then during the anaphase I, homologous chromosomes separate from each other without splitting at the centromere. Hence, sister chromatids remain intact during the anaphase I of meiosis. But, during the metaphase II of meiosis II, individual chromosomes (replicated) align at the cell equator. During anaphase II, centromeres split, and sister chromatids get separated again like in mitosis. Hence, a single-sex cell will consist of a single sister chromatid from each chromosome.

What are Nonsister Chromatids?

Nonsister chromatids are chromatids in each chromosome of a homologous chromosome pair. In the genome, each chromosome with a diploid (2n) chromosome number contain another homologous chromosome. Each homologous chromosome inherits from each parent. Therefore, nonsister chromatids are non-identical since they are inherited from both parents.

Key Difference Between Sister and Nonsister Chromatids

Figure 02: Nonsister Chromatids

Nonsister chromatids contain different alleles of the same gene at the same loci. The pairing of two homologous chromosomes takes place during metaphase I of meiosis. Since they are of the same length, same genes at particular loci, same staining pattern and same centromere position, nonsister chromatids are also referred to as homologous. Nonsister chromatids mainly involved with sexual reproduction. Most importantly, crossing over and genetic recombination occurs between nonsister chromatids. Thus, it leads to genetic diversity within the gametes. Hence, it is an important evolutionary process.

What are the Similarities Between Sister and Nonsister Chromatids?

Both sister and nonsister chromatids are produced during replication of DNA.
They both occur in pairs.
ALso, both sister and nonsister chromatids contain alleles of the same gene. Sister chromatids contain same alleles wile nonsister chromatids contain different alleles.
Besides, both types of chromatids separate from each other during cell division.

What is the Difference Between Sister and Nonsister Chromatids?

There are two types of chromatids visible during the cell division namely sister chromatids and nonsister chromatids. Sister chromatids are the chromatids of the same chromosome that are separated by the centromere and contained same alleles at the same loci. On the other hand, nonsister chromatids are the chromatids of a homologous chromosome pair that contain different alleles of the same gene at the same loci. Hence, the key difference between sister and nonsister chromatids is that the sister chromatids are identical while nonsister chromatids are non-identical.

Furthermore, sister chromatids appear at the interphase of the cell division while the nonsister chromatids appear at the metaphase I of the meiosis I. Thus, it is also a difference between sister and nonsister chromatids. Also, another difference between sister and nonsister chromatids is that the crossing over occurs between nonsister chromatids while it is not seen between sister chromatids. Most importantly, exchange of genetic material occurs between nonsister chromatids while the exchange of genetic material does not occur between sister chromatids. Therefore, it is also a difference between sister and nonsister chromatids.

Below infographic on the difference between sister and nonsister chromatids explains these differences.

Summary – Sister vs Nonsister Chromatids

Sister chromatids are two replicated chromatids of a chromosome joined together by a centromere. On the other hand, nonsister chromatids are chromatids in different chromosomes of a homologous chromosome pair. The key difference between sister and nonsister chromatids is that sister chromatids contain the same allele in the same loci while nonsister chromatids contain different alleles of the same gene in the same loci. However, both sister and nonsister chromatids consist of either the same or different alleles of a gene at the same loci. Sister chromatids locate on the same chromosome. Hence, they are identical copies. But, nonsister chromatids locate in a homologous chromosome pair coming from each parent hence they are not identical. This is the summary of the difference between sister and nonsister chromatids.

Reference:

1. “Chromatid: Definition & Exchange.” Study.com, Study.com. Available here
2. Editors. “Sister Chromatids – Definition, Functions and Structure.” Biology Dictionary, Biology Dictionary, 29 Apr. 2017. Available here