What is Meiosis?
Meiosis is a specialized type of cell division that produces four haploid gametes (sperm or egg cells) from one diploid parent cell. It shuffles genetic material through independent assortment and crossing over, driving genetic diversity.
Meiosis is a two-round nuclear division (meiosis I and II) that halves the chromosome number, producing four genetically unique haploid gametes from one diploid cell.
- •Homologous chromosomes pair and cross over
- •Separates homologous pairs, not sister chromatids
- •Chromosome number is halved (diploid → haploid)
- •Produces genetic recombination
- •No further DNA replication beforehand
- •Separates sister chromatids (like mitosis)
- •Produces four haploid cells total
- •Ensures each gamete has one chromatid per chromosome
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Step-by-step worked examples
A species has 4 chromosome pairs (n = 4). How many genetically distinct gametes can independent assortment alone produce?
C = 2^n C = 2^4 = 16 combinations
Garden peas, the organism Mendel studied, have n = 7 chromosome pairs. How many gamete combinations are possible?
C = 2^n C = 2^7 = 128 combinations
Humans have n = 23 chromosome pairs. How many chromosomally distinct gametes can one person produce (ignoring crossing over)?
C = 2^n C = 2^23 = 8,388,608 combinations
Flashcards
Quick quiz
Q1.How many haploid gametes does one diploid cell produce through meiosis?
Q2.A species has n = 5 chromosome pairs. How many gamete combinations are possible from independent assortment?
Q3.Crossing over occurs during which stage?
Q4.What is separated during meiosis II?
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Common mistakes
Meiosis produces two diploid cells like mitosis. — Correct: Meiosis produces four haploid cells with half the chromosome number.
All four gametes from meiosis are genetically identical. — Correct: Crossing over and independent assortment make each gamete genetically unique.
DNA replicates before both meiosis I and meiosis II. — Correct: DNA replicates only once, before meiosis I; meiosis II has no further replication.
Meiosis and mitosis serve the same biological purpose. — Correct: Mitosis is for growth/repair (identical diploid cells); meiosis is for sexual reproduction (varied haploid gametes).
FAQ
What is meiosis?
Meiosis is the cell division that produces four haploid gametes from one diploid cell for sexual reproduction.
What is the formula for possible gamete combinations?
C = 2^n, where n is the haploid chromosome number — each pair can align two ways during independent assortment.
What are examples of gamete formation by meiosis?
Sperm formation (spermatogenesis) and egg formation (oogenesis) in humans, and pollen/ovule formation in plants.
How do you calculate meiosis gamete diversity?
Raise 2 to the power of the haploid chromosome number (2^n); humans get 2^23 ≈ 8.4 million combinations, before counting crossing over.