Sister chromatids

Definition

Sister chromatids are identical copies of a single chromosome, connected by a region called the centromere. They form during the S phase of the cell cycle, when DNA is replicated, ensuring that each new cell will receive an exact copy of the genetic material during cell division. Their existence is crucial for the accurate segregation of chromosomes during mitosis and meiosis.

5 Must Know Facts For Your Next Test

1. Sister chromatids are formed during DNA replication in the S phase, leading to two identical copies of each chromosome, which remain connected at the centromere until they are separated during mitosis or meiosis.
2. During mitosis, sister chromatids are pulled apart into two separate daughter cells, ensuring that each cell receives an identical set of chromosomes.
3. In meiosis, sister chromatids play a crucial role in both meiosis I and II, but their separation occurs at different stages, leading to genetic diversity in gametes.
4. Each chromosome consists of one chromatid prior to replication; after replication, it becomes two sister chromatids, effectively doubling the amount of genetic material temporarily until division occurs.
5. The accurate separation of sister chromatids is essential for maintaining chromosome number across generations of cells and preventing conditions like aneuploidy.

Review Questions

• How do sister chromatids ensure accurate chromosome segregation during cell division?
  • Sister chromatids ensure accurate chromosome segregation by remaining connected at the centromere until they are separated during mitosis or meiosis. This connection allows spindle fibers to attach properly and pull each chromatid to opposite poles of the cell. When they are separated correctly, each daughter cell receives an identical set of chromosomes, which is vital for maintaining genetic stability.
• Discuss the differences in the role of sister chromatids between mitosis and meiosis.
  • In mitosis, sister chromatids are separated during anaphase to produce two genetically identical daughter cells. In contrast, meiosis involves two rounds of division: during meiosis I, homologous chromosomes (each consisting of sister chromatids) are separated, while in meiosis II, sister chromatids are separated just like in mitosis. This difference contributes to genetic diversity in gametes produced through meiosis as opposed to the identical cells produced by mitosis.
• Evaluate the implications of errors in sister chromatid separation on human health.
  • Errors in sister chromatid separation can lead to aneuploidy, which is an abnormal number of chromosomes in a cell. This can result in conditions such as Down syndrome (trisomy 21), Turner syndrome (monosomy X), or other genetic disorders. Such abnormalities often arise from nondisjunction during meiosis or mitosis, highlighting the critical importance of precise chromatid separation for proper development and cellular function.

Related terms

Chromosome: A structure made of DNA and proteins that contains genetic information, which is organized into genes.

Centromere: The region of a chromosome where sister chromatids are joined and where the spindle fibers attach during cell division.

Mitosis: A process of cell division that results in two genetically identical daughter cells, where sister chromatids are separated to ensure proper genetic distribution.