Explains meiosis as a specialised division that halves chromosome number and generates genetic variation, covering interphase DNA replication, then Meiosis I (reductional division) and Meiosis II (equational division). Prophase I receives the most detail, with its five substages from leptotene to diakinesis, the synaptonemal complex, crossing over and chiasmata. The note closes with how four haploid gametes arise, using human chromosome counts throughout.
Topic 29 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 5 sections, about 526 words (4 min of reading), with 11 flashcards.
In this note
Meiosis. Origin of the gametes.
Meiosis
Meiosis Interphase
Meiosis I (Reductional Division)
Meiosis II (Equational Division)
Meiosis
New cells are made by division of existing cells, which involves the division of both the nucleus and cytoplasm.
In eukaryotes, two types of division take place: mitosis and meiosis.
Meiosis is a unique form of cellular differentiation, initiated usually only once in the life cycle of a eukaryote. It involves an accurate reduction in chromosome number and precise partitioning of genetic material.
Meiosis fulfills two key functions in organisms that reproduce sexually:
It produces a haploid phase in the life cycle.
It generates genetically distinct progeny through recombination.
A proper, functional set of chromosomes is essential during development. Since meiosis is an ordered process, genes and proteins tightly regulate and conserve these events across all eukaryotes.
Meiosis Interphase
G1 Phase (Growth 1)
Chromosomes are made of a single DNA molecule.
In humans: 46 chromosomes (2N), same as somatic cells.
S Phase (Synthesis)
DNA replication occurs.
Each chromosome duplicates → forms two identical sister chromatids.
Interphase is followed by Meiosis I and Meiosis II.
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