Complex sentence: Although a chromosome contains genes that are passed down from parents to children via independent assortment from only one of the two parents, genetic recombination (chromosomal crossover) mixes genes from non-sister chromatids from both parents during meiosis, thus changing the nature of the chromosome.
Split into simpler sentences: Although a chromosome contains a set of genes and is passed down from parents to children via independent assortment from only one of the two parents. But genetic recombination (chromosomal crossover) mixes genes from non-sister chromatids from both parents during meiosis, thus changing the nature of the chromosome.