BRAINCAKEThe Process of Meiosis
Meiosis involves two nuclear divisions: Meiosis I and Meiosis II. They normally occur in succession.
In prophase 1, the nuclear membrane disintegrates, the nucleolus disappears and the chromosomes shorten and thicken and become visible. Homologous chromosomes pair up in a p rocess called synapsis. The chromatids of homologous chromosome overlap and exchange genetic material in a process called crossing over. The points at which they cross over are called chiasmata.
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Key terms in this lesson
- nucleolus
- A dense structure within the nucleus where ribosomal RNA is made and ribosomes are assembled.
- mitosis
- Nuclear division that produces two daughter nuclei, each genetically identical to the parent nucleus.
- centromere
- The region of a chromosome where the two sister chromatids are held together and where spindle fibres attach.
- chromatid
- One of two identical copies of a chromosome, joined at the centromere, formed by DNA replication.
- spindle fibres
- Protein fibres that extend across a dividing cell and attach to the centromeres of chromosomes, pulling them apart.
More in Genetic Diversity
- Substitution of Bases
- Deletion of Bases
- Polyploidy and Hybrids
- Meiosis
- Genetic Recombination by Crossing Over
- Independent Segregation of Chromosomes
- Independent Segregation of Chromatids
- Number of Chromosome Combinations
All 19 lessons in Genetic Diversity · All AQA AS-level Biology topics