Meiosis

noun (uncountable)

/maɪˈəʊsɪs/

Meiosis is a specialised type of eukaryotic cell division that reduces the chromosome number by half (from diploid 2n to haploid n), producing four genetically non-identical gametes (sperm, eggs, or spores) through two consecutive divisions — meiosis I (reductional) and meiosis II (equational). Crossing-over during prophase I generates genetic recombination, the primary source of genetic variation upon which natural selection acts. Understanding meiotic abnormalities is clinically significant: non-disjunction during meiosis I or II produces aneuploid gametes, leading to conditions such as Down syndrome (trisomy 21), which has an estimated prevalence of 1 in 800 to 1,000 live births in India.

✍️ Usage in a UPSC answer

Non-disjunction events during meiosis I in maternal oocytes account for approximately 95% of cases of trisomy 21, the chromosomal basis of Down syndrome, making meiotic regulation a focus of India's national genetic counselling programmes.

Synonyms

reduction divisiongametogenesis divisionreductional divisionsexual cell division

Antonyms

mitosissomatic divisionequational division (partialfor meiosis I only)

🌱 Word Family

meiotic (adjective), meiotically (adverb), meiosporogenesis (noun, rare)

🔡 Root

Greek meiōsis = diminution, lessening; from meioun = to make smaller; from meion = less

📜 Etymology

The term was introduced by J.B. Farmer and J.E.S. Moore in 1905 to describe the reduction division, from Greek meiōsis (a lessening), derived from meioun (to lessen or diminish) and the root meion (less). This Greek root also appears in 'meander' (indirectly) and 'Miocene' (lesser recent). The word precisely captures the defining feature of the process: reduction of the chromosome complement.

🧠 Memory Hook

Meiosis = meion (less) — the cell ends up with LESS genetic material. Remember: Meiosis Makes gametes with half the chromosomes. The 'ei' in meiosis looks like the Roman numeral for 2 — two sequential divisions to make four cells.

⚗️ General Science 📖 Seen in: Human Body Systems — Organ Systems, Ph...

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