A homologous pair consists of two chromosomes, one inherited from each parent. Each chromosome in a homologous pair is made up of two sister chromatids that are joined together. Therefore, in a homologous pair, there are a total of four chromatids.
To break it down further, during the S phase of the cell cycle, each chromosome is replicated, resulting in two identical sister chromatids. When we talk about a homologous pair during meiosis or in a diploid organism, we are referring to both the maternal and paternal chromosome. So when you combine the two chromosomes (each having two chromatids), you end up with four chromatids in total. This is crucial for processes like meiosis, where the exchange of genetic material can occur between homologous chromosomes, leading to genetic diversity.