Let’s Present and Clarify the Concepts of Sister Chromatid and Non-Sister Chromatid:
Before cell division, chromosomes in a cell’s nucleus appear as thread-like strands. Each chromosome’s DNA molecule duplicates (through DNA replication) before cell division, such as in meiosis. After replication, each chromosome has two identical copies of DNA. During the first stage of meiotic division, known as Meiosis I, the chromosomes condense. Each condensed chromosome is made up of two strands held together by a kinetochore. These chromosomes align along the cell’s equator during metaphase. Each condensed strand is then referred to as a chromatid. The chromatids can either be sister chromatids or non-sister chromatids. A non-sister chromatid refers to one of the two chromatids of a pair of homologous chromosomes. When a eukaryotic chromosome duplicates before mitosis, the formation of one of the two longitudinally adjacent strands is called a chromatid. Chromatids are joined together at the centromere, and sister chromatids originate from the same chromosome.
Explanation of Sister Chromatids and Non-Sister Chromatids
Sister Chromatids:
Two duplicated chromatids of a chromosome are joined together at the centromere to form sister chromatids. During DNA replication, these chromatids duplicate in the S phase of interphase. Importantly, both sister chromatids have the same allele at corresponding loci. Additionally, during mitosis and meiosis, sister chromatids from the same chromosome behave in different ways.
During metaphase in mitosis, individual chromosomes align at the cell’s equator, allowing the two sister chromatids to separate from each other across the metaphase plate. After the centromere splits during anaphase, the two sister chromatids separate and move to opposite ends of the cell.
Non-Sister Chromatids:
Chromatids that belong to homologous chromosome pairs are called non-sister chromatids. Each chromosome in an organism with a diploid (2n) chromosomal number has a homologous partner. One homologous chromosome is inherited from each parent. Because non-sister chromatids come from different parents, they are not identical.
Each chromosome has a corresponding homologous partner, with one coming from the mother (maternal) and the other from the father (paternal). These pairs of homologous chromosomes are known as non-sister chromatids, and they carry the same genes, but may have different alleles at the corresponding loci.
Let Us Understand: Difference Between Sister Chromatid And Non Sister Chromatid
| S.No. | Sister Chromatid | Non Sister Chromatid |
| 1. | Two replicated chromatids of a chromosome are attached by a centromere to form a sister chromatid. | Chromatids that are placed on distinct chromosomes within a homologous chromosome pair are called as non sister chromatid |
| 2. | Synthesize during the S phase of the interphase | Synthesize during the metaphase I of meiosis |
| 3. | These are placed on the same chromosome | Non sister chromatid are placed in a homologous chromosome pair |
| 4. | In sister chromatids, genetic exchange does not take place during recombination. | Genetic exchange happens between non-sister chromatids during recombination. |
| 5. | Contain same alleles at same loci | Possessing various versions of the same gene at identical positions on homologous chromosomes. |
| 6. | Occur in asexual reproduction | Occur in sexual reproduction |
Characteristics of Sister Chromatids and Non-Sister Chromatids:
- Both sister and non-sister chromatids are formed during DNA replication.
- They exist in pairs.
- Both contain genetic variations of the same gene, where sister chromatids have identical alleles at the same gene locations, while non-sister chromatids may have different alleles at the same gene locations.
- They both separate from each other during cell division.
Recap: What are Sister Chromatids and Non-Sister Chromatids?
Sister chromatids are two duplicated copies of a chromosome, connected by a centromere. Non-sister chromatids, on the other hand, refer to chromatids from different chromosomes of a homologous pair. The key difference between sister and non-sister chromatids is that non-sister chromatids have different versions of the same gene at a given location, while sister chromatids carry the same version of a gene. However, both sister and non-sister chromatids can have identical or varying alleles at the same location. Sister chromatids are found on the same chromosome, making them exact duplicates. Non-sister chromatids are not identical, as they originate from homologous chromosomes contributed by each parent.
