Two successive nuclear divisions that produce gametes or sexual spores that have one-half of the genetic material of the original cell.
The correct answer and explanation is:
Correct Answer: Meiosis
Explanation:
Meiosis is a type of cell division that occurs in sexually reproducing organisms and is responsible for producing gametes (sperm and egg cells in animals) or sexual spores (in fungi and plants). This process involves two successive nuclear divisions, known as meiosis I and meiosis II, which result in four daughter cells, each containing half the number of chromosomes as the original parent cell. This reduction in chromosome number is essential to maintain the species-specific chromosome number across generations when gametes fuse during fertilization.
The process begins with one diploid (2n) cell that undergoes meiosis I, where homologous chromosomes pair up and then separate into two different cells. This division reduces the chromosome number from diploid to haploid (n), making it a reductional division. Meiosis I also includes crossing over, a process where genetic material is exchanged between homologous chromosomes, increasing genetic diversity.
Meiosis II resembles mitosis, where the sister chromatids of each chromosome separate. Unlike mitosis, though, meiosis II begins with haploid cells and ends with haploid cells, so it does not change the chromosome number. This phase is referred to as an equational division because it maintains the haploid state.
The outcome of meiosis is four genetically unique haploid cells, each with one set of chromosomes. This genetic variation is crucial for evolution and adaptation in populations. Meiosis plays a central role in heredity and the life cycle of organisms, ensuring genetic continuity and diversity from one generation to the next. It contrasts with mitosis, which produces identical cells for growth and repair and does not reduce the chromosome number.