What are bivalent or tetrad?
The correct answer and explanation is:
A bivalent, also known as a tetrad, is a structure formed during meiosis, the process by which gametes (sperm and eggs) are produced. A bivalent consists of two homologous chromosomes that pair up during the first stage of meiosis. Each homologous chromosome consists of two sister chromatids, so the bivalent contains four chromatids in total, forming a structure referred to as a tetrad.
In meiosis, homologous chromosomes are chromosomes that have the same genes but may have different versions, or alleles, of those genes. These chromosomes come together during prophase I of meiosis. The process of homologous recombination or crossing over occurs during this phase, where sections of chromatids are exchanged between the paired homologous chromosomes. This exchange increases genetic diversity, as it allows for new combinations of genes that were not inherited directly from the parents.
The bivalent structure is crucial for ensuring proper segregation of chromosomes during meiosis. In metaphase I, the tetrad aligns along the metaphase plate, and spindle fibers attach to the centromeres of each chromosome. In anaphase I, the homologous chromosomes are pulled apart, but the sister chromatids of each chromosome remain attached until later in meiosis II. This ensures that each gamete receives only one chromosome from each pair of homologs, maintaining the correct chromosome number in the resulting gametes.
Overall, the bivalent or tetrad is essential in the process of genetic recombination and accurate chromosome segregation, both of which are fundamental for producing genetically diverse offspring and maintaining the stability of species’ chromosome numbers across generations.