Mitosis & Meiosis Review: Videos & Practice Problems

The main difference between mitosis and meiosis lies in their outcomes and processes. Mitosis results in two genetically identical daughter cells, each with the same number of chromosomes as the parent cell. It involves one division cycle where sister chromatids separate. In contrast, meiosis consists of two division cycles (meiosis I and meiosis II) and results in four genetically diverse daughter cells, each with half the number of chromosomes of the parent cell. Meiosis I separates homologous chromosomes, while meiosis II separates sister chromatids. This reduction in chromosome number is crucial for sexual reproduction, ensuring genetic diversity.

DNA replication is crucial before both mitosis and meiosis because it ensures that each daughter cell receives a complete set of genetic information. During the S phase of the cell cycle, DNA is replicated, resulting in two identical copies of each chromosome, known as sister chromatids. In mitosis, these sister chromatids are separated into two identical daughter cells. In meiosis, DNA replication occurs before meiosis I, ensuring that homologous chromosomes can be properly separated, and then sister chromatids are separated in meiosis II. Without DNA replication, cells would not have the necessary genetic material to function properly.

Meiosis contributes to genetic diversity through two main mechanisms: crossing over and independent assortment. During prophase I of meiosis, homologous chromosomes pair up and exchange genetic material in a process called crossing over. This results in new combinations of genes on each chromosome. Additionally, during metaphase I, homologous chromosome pairs align randomly at the cell's equator, leading to independent assortment. This random distribution of maternal and paternal chromosomes to the daughter cells further increases genetic variation. These processes ensure that each gamete (sperm or egg) is genetically unique, contributing to the genetic diversity of offspring.

Sister chromatids are two identical copies of a single chromosome that are connected by a centromere. They are formed during DNA replication in the S phase of the cell cycle. In mitosis, sister chromatids separate during anaphase, ensuring that each daughter cell receives an identical set of chromosomes. In meiosis, sister chromatids do not separate during meiosis I; instead, homologous chromosomes are separated. Sister chromatids finally separate during anaphase II of meiosis II, resulting in four genetically diverse haploid cells. This separation is crucial for maintaining the correct chromosome number in sexually reproducing organisms.

Meiosis plays a critical role in sexual reproduction by producing gametes (sperm and eggs) with half the number of chromosomes as the parent cell. This reduction in chromosome number is essential because it ensures that when two gametes fuse during fertilization, the resulting zygote has the correct diploid number of chromosomes. Meiosis also introduces genetic diversity through crossing over and independent assortment, which are vital for the evolution and adaptation of species. The genetic variation produced by meiosis contributes to the unique combination of traits in offspring, enhancing the survival and adaptability of populations.