Meiosis halves; fertilisation restores
| English | 中文 | Pinyin |
|---|---|---|
| meiosis/meɪˈəʊsɪs/ | 减数分裂 | jiǎn shù fēn liè |
| fertilisation/ˌfɜːtɪlaɪˈzeɪʃn/ | 受精 | shòu jīng |
What would explain this observation?
- If gametes kept the ordinary body-cell chromosome number, fusion would double it each generation. Meiosis 减数分裂 solves that problem before fertilisation 受精.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Cells in reproductive organs divide by meiosis to form gametes. Genetic information is copied and the cell divides twice, forming four gametes. Each has one set of chromosomes and the gametes are genetically different. GCSE Biology requires this overall account, not recall of named meiotic stages or detailed chromosome-exchange mechanisms.
- meiosis: Division producing gametes with one chromosome set; fertilisation: Fusion of gametes restoring the normal chromosome number.
A model species has 24 chromosomes in ordinary cells. What number should a gamete contain?
Fusion of two gametes restores the normal number of chromosomes in the new cell. The new cell divides by mitosis, increasing the number of cells. As the embryo develops, cells differentiate and become specialised. Copying DNA before division does not mean the final gametes keep two chromosome sets.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Fusion of two gametes restores the normal number of chromosomes in the new cell. The new cell divides by mitosis, increasing the number of cells. As the embryo develops, cells differentiate and become specialised. Copying DNA before division does not mean the final gametes keep two chromosome sets.
- Use coloured chromosome cards to represent sets, label a body cell and gamete clearly, and trace two gametes into one fertilised cell. Keep chromosome number separate from the number of cells. State that a simple card model demonstrates number conservation rather than all mechanisms producing variation.
Which two habits make the investigation or model in this case more defensible?
Use coloured chromosome cards to represent sets, label a body cell and gamete clearly, and trace two gametes into one fertilised cell. Keep chromosome number separate from the number of cells. State that a simple card model demonstrates number conservation rather than all mechanisms producing variation.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: in a fictional species, an ordinary cell has 18 chromosomes. Each gamete has 9. Fertilisation combines 9+9 to restore 18; later mitosis maintains 18 in each ordinary daughter cell. Four gametes each having 9 means 36 chromosomes across four separate cells, not 36 within each gamete.
A fictional species has 32 chromosomes in ordinary cells. Find the number in a gamete. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A fictional species has 32 chromosomes in ordinary cells. Find the number in a gamete.
The result is 16 chromosomes. Known: in a fictional species, an ordinary cell has 18 chromosomes. Each gamete has 9. Fertilisation combines 9+9 to restore 18; later mitosis maintains 18 in each ordinary daughter cell. Four gametes each having 9 means 36 chromosomes across four separate cells, not 36 within each gamete.
Check the conclusion and its limits
- Meiosis does not make four identical ordinary body cells. Fertilisation is fusion rather than a division. The four-cell outcome is the specification’s overall model; detailed gamete development and stage names are outside this objective.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Fertilisation halves the chromosome number. This claim is false: Meiosis does not make four identical ordinary body cells. Fertilisation is fusion rather than a division. The four-cell outcome is the specification’s overall model; detailed gamete development and stage names are outside this objective.
Meiosis halves; fertilisation restores: Fusion of two gametes restores the normal number of chromosomes in the new cell. The new cell divides by mitosis, increasing the number of cells. As the embryo develops, cells differentiate and become specialised. Copying DNA before division does not mean the final gametes keep two chromosome sets.
Fertilisation halves the chromosome number.
Meiosis does not make four identical ordinary body cells. Fertilisation is fusion rather than a division. The four-cell outcome is the specification’s overall model; detailed gamete development and stage names are outside this objective.
Division producing gametes with one chromosome set: write the technical term.
meiosis means Division producing gametes with one chromosome set.