Sexual reproduction requires meiosis, a process in which a parent cell divides to produce cells with half the genetic material of the parent. A diploid parent cell, for example, divides to make four haploid cells. In sexual reproduction, haploid gametes from two individuals then combine to produce a diploid zygote. An offspring resulting from sexual reproduction is genetically different from both parents.
In the accompanying animation, we examine the events of meiosis, using a model cell with two pairs of chromosomes. One chromosome of each pair is maternally derived, while the other is paternally derived; each is distinguished by different colors. The colors allow us to track two mechanisms of producing unique daughter cells: independent assortment of chromosomes and the phenomenon of crossing over.
Meiosis and sexual reproduction produce genetic diversity.
When a diploid cell divides by meiosis to produce gametes, each of the four daughter cells is genetically unique. The uniqueness arises in part from the independent assortment of chromosomes in meiosis. Through independent assortment, each daughter cell randomly receives either a maternally derived homolog or the paternally derived homolog from each chromosome pair. In addition, the process of crossing over produces chromosomes that have unique combinations of paternally and maternally derived regions.
This shuffling of the genetic material produces genetically unique gametes, each of which can then fuse with another unique gamete during fertilization to produce a unique zygote of the next generation.
Textbook Reference: Concept 7.4 Meiosis Halves the Nuclear Chromosome Content and Generates Diversity