What describes a tetrad in genetics?

A tetrad in genetics specifically refers to a structure formed during meiosis, particularly in prophase I, where homologous chromosomes pair up. Each tetrad consists of four chromatids – two from each homologous chromosome. This pairing is crucial for the process of genetic recombination or crossing over, where segments of DNA are exchanged between homologous chromosomes, leading to genetic variation in the resulting gametes.

In contrast, while sister chromatids are identical copies formed during DNA replication, they do not constitute a tetrad since they are not homologous chromosomes but rather two copies of the same chromosome. Identical alleles refer to versions of a gene that are exactly the same, which doesn't specifically describe the chromosomal structure involved in a tetrad. Non-homologous chromosomes are chromosomes that do not correspond to each other in terms of their gene loci and pairing; thus, they are not involved in the formation of tetrads. This is why a tetrad is accurately described by the pairing of homologous chromosomes.