AP BIOLOGY

Detailed explanation-1: -During prophase I, the homologous chromosomes condense and become visible as the x shape we know, pair up to form a tetrad, and exchange genetic material by crossing over. During prometaphase I, microtubules attach at the chromosomes’ kinetochores and the nuclear envelope breaks down.

Detailed explanation-2: -During prophase I, the pairs of homologous chromosomes come together to form a tetrad or bivalent, which contains four chromatids. Recombination can occur between any two chromatids within this tetrad structure.

Detailed explanation-3: -These chromosomes are called homologous pairs. As a cell undergoes meiosis, when homologous chromosomes line up together, they form a tetrad. Tetrads consist of two homologous chromosomes, with a total of four sister chromatids held together by a structure named the chiasmata.

Detailed explanation-4: -Between prophase I and metaphase I, the pairs of homologous chromosome form tetrads. Within the tetrad, any pair of chromatid arms can overlap and fuse in a process called crossing-over or recombination. Recombination is a process that breaks, recombines and rejoins sections of DNA to produce new combinations of genes.

Detailed explanation-5: -In Prophase 1 the two homologous chromosomes align one next to the other. A Chromosome consists of two sister chromatids so 2 chromosomes correspond to 4 chromatids. Hence the “tetrad".