16.1.316 · Inherited Change
Meiosis in Animal and Plant Cells — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 10 parts Lesson 4 of 18 1 quiz
Lesson summary
16.1.3 Meiosis in Animal and Plant Cells — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe the stages of meiosis I and meiosis II in animal and plant cells.Definition — nuclear division that produces haploid cells from diploid cells.Gametes — it produces game…
- Chromatids
- Crossing over
- Metaphase I
- Anaphase I
- Centromeres
- Telophase I
Part 1 of 8Overview of meiosis
1Definition
- Definition nuclear division that produces haploid cells from diploid cells.
2Gametes
- Gametes it produces gametes in plants and animals for sexual reproduction.
3Divisions
- Divisions meiosis I and meiosis II.
4Stages
- Stages each division has prophase, metaphase, anaphase and telophase.
Part 2 of 8Prophase I
1DNA
- DNA condenses and becomes visible as chromosomes.
2Chromatids
- DNA replication has already occurred, so each chromosome has two sister chromatids joined at a centromere.
3Pairing
- Pairing homologous chromosomes lie side by side as a bivalent.
4Crossing over
- Crossing over non-sister chromatids may cross over at the chiasmata.
5Spindle
- Spindle centrioles move to opposite poles and the spindle forms.
6Nucleus
- Nucleus the nuclear envelope breaks down and the nucleolus disintegrates.
Part 3 of 8Metaphase I and anaphase I
1Metaphase I
- Metaphase I bivalents line up along the equator, with spindle fibres attached to the centromeres.
2Anaphase I
- Anaphase I homologous pairs separate as microtubules pull whole chromosomes to opposite ends.
3Centromeres
- Centromeres do not divide.
Part 4 of 8Telophase I and cytokinesis
1Telophase I
- Telophase I chromosomes arrive at the poles, the spindle breaks down, and nuclear envelopes and nucleoli reform.
2Result
- Result two haploid cells, because each has half the number of centromeres.
3Animal cells
- Animal cells the membrane pinches inwards, forming a cleavage furrow.
4Plant cells
- Golgi vesicles gather at the cell plate and merge to form the new membrane, then cellulose walls are laid down.
Part 5 of 8Meiosis II
1
There is no interphase between the two divisions and no DNA replication.
2
Prophase II: the nuclear envelope breaks down, chromosomes condense and a spindle forms at right angles to the old one.
3
Metaphase II: chromosomes line up in single file on the equator.
4
Anaphase II: centromeres divide and chromatids are pulled to opposite poles.
5
Telophase II: nuclear envelopes form around four groups of chromosomes.
6
Cytokinesis: four haploid cells form.
Part 6 of 8Chromosomes and chromatids
Counting
- Counting chromosomes are counted by centromeres.
Replication
- Replication after interphase 46 chromosomes still have 46 centromeres but 92 chromatids.
Meiosis II
- Meiosis II each chromosome has two chromatids, with half the chromosome number of the original cell.
Part 7 of 8Comparison of the divisions
| Feature | Meiosis I | Meiosis II |
|---|---|---|
| Pairs of chromosomes | Yes, bivalents | No |
| Separated in anaphase | Whole chromosomes | Chromatids |
| Cells formed | Two | Four |
| DNA replication before | Yes | No |
Part 8 of 8More from the specification
More from the specification
Independent assortment generating genetic variation
- Independent assortment generating genetic variation random alignment of bivalent pairs across the middle equatorial plate generates extensive genetic variation among gametes.
Fertilisation and diploid zygote formation
- Fertilisation and diploid zygote formation haploid gametes containing parental alleles fuse during fertilisation, restoring diploid chromosome numbers within the resulting single-celled zygote.
Cytokinesis in animal and plant cells
- Cytokinesis in animal and plant cells animal cells pinch cytoplasm via cleavage furrows,
- whereas plant cells deposit cellulose plates during telophase division.
Meiotic division and haploid gamete formation
- Meiosis consists of two successive nuclear divisions that reduce chromosome number from diploid (2n) to haploid (n),
- (meiosis I and II)
- producing four genetically distinct gametes.
Crossing over and chiasmata
- During prophase I, non-sister chromatids of homologous chromosomes exchange genetic segments at chiasmata,
- producing recombinant chromatids with novel allele combinations.
Independent assortment of bivalents
- Random orientation of maternal and paternal homologous pairs at the metaphase I plate generates 2^n possible chromosome combinations in daughter gametes.
Daughter cell
- Cell produced by cell division.
Variation
- Differences between individuals of the same species.
Allele
- A version of a gene.
Zygote
- The diploid cell formed by fertilisation.
Cytoplasm
- The jelly in which the cell's chemical reactions happen.
Photomicrograph
- A photograph taken through a light microscope.
Genetic variation
- Differences in alleles within a population.
Independent assortment
- Random sorting of chromosome pairs into gametes.
Reduction division
- Division that halves the chromosome number.
Key terms
| Term | Meaning |
|---|---|
| Bivalent | Pair of homologous chromosomes. |
| Chiasma | Point where non-sister chromatids cross over. |
| Cleavage furrow | Inward pinching of an animal cell membrane. |
| Cell plate | Structure formed by Golgi vesicles in plant cytokinesis. |
| Sister chromatids | Two identical copies of a chromosome joined at a centromere. |
| Equator | Middle of the spindle where chromosomes line up. |
Avoid these mistakes
1
Saying the centromeres divide in anaphase I — they divide in anaphase II.
2
Saying chromatids separate in meiosis I — homologous chromosomes do.
3
Saying DNA replicates before meiosis II — it does not.
4
Saying plant cells have a cleavage furrow — they form a cell plate.
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