Virginia 7th Grade Science SOL Practice Test

Genetic variation in sexual reproduction comes from mixing genetic material from two parents and from the reshuffling of genes during meiosis. During meiosis, homologous chromosomes exchange segments in a process called crossing over, creating chromosomes with new combinations of alleles. At the same time, the way chromosomes are independently assorted into gametes means each gamete carries a different set of parental alleles. When a sperm and egg meet in fertilization, their randomly chosen genetic material combines to form a zygote with a unique genetic makeup. This combination of two parents’ alleles plus recombination during meiosis is what drives the variety seen in offspring. While mutations can add new changes, and fertilization adds even more variety, the core mechanism described here is the mixing and rearranging of parental genes through crossing over and independent assortment.