Difference Between Sister and Nonsister Chromatids

Main Difference – Sister Chromatids vs Nonsister Chromatids

Sister chromatids and nonsister chromatids are the two types of chromatids found in a cell that undergoes cell division. Chromatids are produced during the early stages of cell division. Sister chromatids are replicated from the same chromosome whereas nonsister chromatids appear during the metaphase I of meiosis. Sister chromatids are joined together by the centromere. Nonsister chromatids are found in the homologous chromosome pair on the cell equator. The main difference between sister and nonsister chromatids is that sister chromatids contain the same allele in the same loci whereas nonsister chromatids contain different alleles of the same gene in the same loci.

Key Areas Covered

1. What are Sister Chromatids
      – Definition, Features, Role in Cell Division
2. What are Nonsister Chromatids
      – Definition, Features, Role in Cell Division
3. What are the Similarities Between Sister Chromatids and Nonsister Chromatids
      – Outline of Common Features
4. What is the Difference Between Sister and Nonsister Chromatids
      – Comparison of Key Differences

Key Terms: Allele, Centromere, Homologous Recombination, Interphase, Loci, Meiosis, Mitosis, Nonsister Chromatids, Sister Chromatids

What are Sister Chromatids

The two chromatids of a replicated chromosome which are connected by the centromere are referred to as sister chromatids. The replication of chromosomes of a cell occurs at the S phase of the interphase. Each pair of sister chromatids consists of the same allele at the same loci. During the metaphase of mitosis, individual, replicated chromosomes align at the cell equator. During anaphase, sister chromatids are separated from each other and move to the opposite poles. During metaphase I of meiosis, homologous chromosomes pair at the cells equator. Sister chromatids remain the same during anaphase I. Individual, replicated chromosomes align at the cell equator during metaphase II. The separation of sister chromatids occurs at anaphase II. Ultimately, each sex cell contains a single sister chromatid from each chromosome. The sister chromatids in a replicated chromosome are shown in figure 1.

Main Difference - Sister Chromatids vs Nonsister Chromatids

Figure 1: Sister Chromatids

What are Nonsister Chromatids

The chromatids in different chromosomes of a homologous chromosome pair are referred to as nonsister chromatids. Each chromosome with a diploid chromosome number in the genome consists of another homologous chromosome. Each homologous chromosome is inherited from each parent. Both chromosomes of the homologous pair contain different alleles of the same gene at the same loci. These two homologous chromosomes pair during the metaphase I of meiosis. The nonsister chromatids are also known as homologs since they are of the same length, same centromere position, and have the same staining pattern, and same genes at particular loci. Once homologous chromosomes pair with each other, chromosomal crossover can occur between nonsister chromatids of each pair. Crossover occurs from chiasmata during prophase I of meiosis. The process is called homologous recombination. Homologous recombination is one of the causes for genetic variation among individuals within the same population. Chromosomal crossover, occurring between nonsister chromatids is shown in figure 2.

Difference Between Sister Chromatids and Nonsister Chromatids

Figure 2: Chromosomal Crossover

Similarities Between Sister and Nonsister Chromatids

Both sister chromatids and nonsister chromatids always occur in pairs.
Both sister chromatids and nonsister chromatids are produced during DNA replication during the S phase of the interphase.
Both sister chromatids and nonsister chromatids separate from each other during cell division.
Both sister chromatids and nonsister chromatids contain either the same or different alleles of a gene at the same loci.

Definition

Sister Chromatids: Sister chromatids are the two chromatids of a replicated chromosome, which are connected by the centromere.

Nonsister Chromatids: Nonsister chromatids are two chromatids from two different homologous chromosomes.

Identity

Sister Chromatids: Sister chromatids are identical to each other since they are produced by DNA replication.

Nonsister Chromatids: Since each nonsister chromatid is inherited from each parent, nonsister chromatids are non-identical.

Alleles

Sister Chromatids: Sister chromatids contain the same alleles at the same loci.

Nonsister Chromatids: Nonsister chromatids contain different alleles of same genes at the same loci.

Produced in

Sister Chromatids: Sister chromatids are produced in the S phase of the interphase.

Nonsister Chromatids: Nonsister chromatids are formed during the metaphase I of meiosis.

Found in

Sister Chromatids: Sister chromatids are found on the same chromosome.

Nonsister Chromatids: Nonsister chromatids are found in a homologous chromosome pair.

Involved in

Sister Chromatids: Sister chromatids are involved in asexual reproduction.

Nonsister Chromatids: Nonsister chromatids are involved in sexual reproduction.

Conclusion

Sister chromatids and nonsister chromatids are results of DNA replication. Sister chromatids are the two chromatids that originate from the same chromosome. Therefore, each locus of both chromatids consists of the same allele. Each sister chromatid comprises a nonsister chromatid in its other homologous chromosome. Nonsister chromatids consist of different alleles at each locus since their origination is different. The main difference between sister and nonsister chromatids is the similarity or difference of alleles found at each locus.

Reference:

1. Bailey, Regina. “What Are Sister Chromatids?” ThoughtCo. N.p., n.d. Web. Available here. 30 July 2017.
2. “Non-sister chromatids.” The School of Biomedical Sciences Wiki. N.p., n.d. Web. Available here. 30 July 2017.

Image Courtesy:

1. “Chromosomal Crossover” By Abbyprovenzano – Own work (CC BY-SA 3.0) via Commons Wikimedia