Biology Genetics Practice Test

In a diploid organism, there are two versions of each chromosome—one from each parent. When these two chromosomes carry the same genes in the same order, they are called homologous chromosomes. They may carry different alleles at various gene locations, which is where variation among individuals comes from. This pairing happens because homologs come from different parents, and during meiosis they align and can exchange genetic material, increasing diversity. By contrast, sister chromatids are identical copies of a single chromosome produced during DNA replication, and they stay attached until they separate later in cell division. Alleles are just the different versions of a gene that can reside at the same locus on homologous chromosomes. Chromatids simply refers to the duplicated copies of a chromosome, not to the chromosome from each parent.