Meiosis — Science definition

Defined in 2 courses:

Where it is taught

In use

That something is meiosis, the division that produces gametes — sex cells carrying half a set.

Meiosis, Gametes & Genetic Variation

That something is meiosis, a special kind of cell division that produces gametes — sperm and egg cells.

Meiosis & Sexual Reproduction

Questions using meiosis

Problem 1

Why is one mitotic division not a sufficient meiosis model?
Answer and explanation

It normally preserves the paired set rather than producing the reduced gamete set through the studied two-division process.

Problem 2

The main job of meiosis is to produce
  1. two identical body cells for growth
  2. new proteins from mRNA
  3. an exact copy of a single chromosome
  4. four haploid gametes (sex cells) with half the chromosome number
Answer and explanation

four haploid gametes (sex cells) with half the chromosome number

Meiosis makes four haploid gametes, each with half the parent cell's chromosome number.

Problem 3

Explain why meiosis (followed by fertilization) keeps a species' chromosome number constant from one generation to the next.
Answer and explanation

Meiosis halves the chromosome number when it makes gametes, so each gamete carries only one set. When two gametes join at fertilization, the two halves add back up to the full number, keeping it constant instead of doubling each generation.

Problem 4

Compare set number, DNA copies and final products separatelyCompare set number, DNA copies and final products separatelyChromosome counts in a supplied 2n = 4 modelStarting diploid nucleus4After DNA copying4After meiosis I /nucleus2After meiosis II /nucleus2DNA-copy counts differ: 4 → 8 → 4 → 2 per nucleus.
Original chromosome-count account for a two-pair model, not human numbers or all possible errors.
Interpret the supplied visual. Why would “meiosis halves each chromosome” be inaccurate?
Answer and explanation

It reduces chromosome-set number by segregation; chromosomes remain whole structures, with possible exchanged regions.

In the supplied 2n=4 model, DNA replication gives eight chromatids within four replicated chromosomes. After meiosis I each nucleus has two replicated chromosomes and four chromatids; after meiosis II each normally has two unreplicated chromosomes. Typical mitosis instead preserves the starting ploidy in daughter nuclei. This distinguishes division number, chromosome number and DNA content. The standard model predicts variation but does not guarantee that every meiotic product must be different at every locus; sequence, pairing and chance constrain the actual combinations.

It reduces chromosome-set number by segregation; chromosomes remain whole structures, with possible exchanged regions.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

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