What is Meiosis?
Meiosis is the type of cell division that produces gametes — sperm and egg cells — each carrying half the normal chromosome number. Through crossing over and independent assortment it also shuffles genes, creating the genetic variety that makes every offspring unique.
Meiosis is a two-round division (Meiosis I and Meiosis II) that turns one diploid cell into four genetically unique haploid gametes, halving the chromosome number so it's restored at fertilization.
- 1↓InterphaseDNA replicates; each chromosome now has two sister chromatids.
- 2↓Meiosis IHomologous chromosomes pair up, cross over (exchange DNA), then separate into two haploid cells.
- 3↓Meiosis IISister chromatids separate in each cell, similar to mitosis, but starting from a haploid cell.
- 4ResultFour genetically unique haploid gametes are produced from one diploid cell.
Step-by-step worked examples
A human somatic cell has 46 chromosomes. How many chromosomes does each gamete produced by meiosis contain?
Meiosis halves the chromosome number (diploid → haploid) 46 ÷ 2 = 23 Each gamete contains 23 chromosomes
One primary spermatocyte enters meiosis. How many functional sperm cells does it ultimately produce?
Meiosis I splits it into 2 secondary spermatocytes Meiosis II splits each of those into 2 spermatids 2 × 2 = 4 All 4 spermatids mature into functional sperm
A cell with 8 chromosomes (4 homologous pairs) undergoes meiosis. How many different chromosome combinations are possible in its gametes from independent assortment alone?
Possible combinations = 2ⁿ, where n = number of homologous pairs n = 4 2⁴ = 16 So 16 different combinations are possible
Flashcards
Quick quiz
Q1.How many cells does one round of meiosis produce from a single diploid cell?
Q2.Crossing over occurs during which phase?
Q3.If a parent cell has 46 chromosomes, how many does each product of meiosis have?
Q4.What is the main biological purpose of meiosis?
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Common mistakes
Confusing meiosis with mitosis. — Correct: Mitosis makes 2 identical diploid cells for growth/repair; meiosis makes 4 unique haploid gametes for reproduction.
Thinking chromosome number stays the same after meiosis. — Correct: Meiosis halves the chromosome number — diploid (2n) becomes haploid (n).
Believing all four gametes from meiosis are genetically identical. — Correct: Crossing over and independent assortment make each of the four gametes genetically distinct.
Thinking crossing over happens in mitosis too. — Correct: Crossing over is unique to Prophase I of meiosis, not mitosis.
FAQ
What is meiosis?
Meiosis is the cell division process that produces haploid gametes (sperm and eggs) from a diploid parent cell, halving the chromosome number.
What is the meiosis formula for chromosome number?
There's no numeric formula, but the rule is: gamete chromosome number = parent's diploid number ÷ 2.
What are examples of meiosis in humans?
Sperm production in the testes and egg production in the ovaries are the two examples of meiosis in humans.
How is meiosis different from mitosis?
Meiosis has two divisions and produces four unique haploid cells for reproduction; mitosis has one division and produces two identical diploid cells for growth.