Meiosis- A-Level Biology

Meiosis- A-Level Biology

Meiosis- Remember in meiosis produces cell that are genetically different

  • Gametes include sperm cell in males and egg cells in females. They fuse together to form a zygote.
  • One area for confusion is that the diploid number of chromosomes which means that they contain two of each chromosome.
  • Remember that the haploid number of chromosomes there is only one copy in each chromosome.
  • Fertilisation is random process and this results in a different combination of chromosomes which are from both parents.
  • Meiosis takes places in the reproductive organs- in this process cells begin with diploid number of chromosomes and they become the haploid number of chromosomes.

The process of meiosis

  • The first part of meiosis DNA unravels- this replicates which are two copies of each chromosome called chromatids.
  • DNA condenses to form two sister chromatids.
  • There are two meiosis divisions – in meiosis 1 the chromosomes are arranged into homologous pairs.
  • Meiosis 11- pairs of sister chromatids are separated/
  • Four haploid cells are produced which are genetically different.

key words

Gametes, homologous pairs, haploid, diploid and chromatids

Examples of exam questions and tips

     Division of the nucleus by meiosis produces haploid cells from a diploid cell. Nuclei produced by mitosis have the same number of chromosomes as the parent nucleus.

(a)     What is the biological importance of reducing the chromosome number when the cell divides by meiosis?

Later fertilisation/ cell fusion

Restoration of the diploid number of chromosomes (do not specifically write sexual reproduction)

You may be asked the comparison of mitosis and meiosis

In meiosis

Homologous) chromosomes associate in pairs

Crossing-over / chiasmata formation

Two / (nuclear stages) divisions / → 4 offspring cells

Genetically different (product)

In mitosis

(Homologues) independent / do not pair

No crossing-over

One / (nuclear stage) division / → 2 offspring cells;

Genetically identical (product)

 

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