Meiosis I1 Prophase I

Apuntes

• Subtopic: Meiosis I - Prophase I Prophase I is the first stage in the first meiotic division (meiosis I). It is essential mainly for the exchange of DNA between homologous chromosomes via a process called homologous recombination and the crossover at chiasmata between non-sister chromatids. This stage is important to increase genetic variation. It ends with the disintegration of the nucleolus and the nuclear membrane. The chromosomes are completely condensed, and in meiosis, the homologous chromosomes pair with one another. Centrosomes and spindle fibers play a crucial role during this stage. Humans have 23 pairs of homologous chromosomes, making a total of 46 chromosomes. --- • Subtopic: Meiosis I - Metaphase I Metaphase I, the lining-up stage, is relatively rapid. Tetrads, which are pairs of chromosomes with four chromatids, are pulled into line at what is known as the metaphase (or equatorial) plate. This plate does not actually exist but is an imaginary central line along which the chromosomes are positioned. Homologous chromosomes attach to the spindle fibers, and homologous pairs become aligned in the center of the cell. Centrioles and spindle fibers are involved in t...