Final answer:
The condition where sex cells (gametes) contain only one set of chromosomes is called haploid. This is essential in sexual reproduction to form a diploid zygote when two haploid gametes combine. Meiosis is the process by which diploid cells produce haploid gametes, maintaining genetic stability.
Step-by-step explanation:
Sex cells (gametes) contain only one set of chromosomes. This condition is called haploid. Both male gametes (sperm) and female gametes (eggs) are haploid cells, containing a single copy of each homologous chromosome. In sexual reproduction, the fusion of two haploid gametes forms a diploid zygote or fertilized egg, which contains two sets of chromosomes.
In contrast to haploid cells, most body or somatic cells of an organism are diploid, meaning they contain two complete sets of chromosomes, one from each parent. Sexual reproduction ensures the continuation of species by alternating between haploid and diploid states through the processes of meiosis and fertilization. Meiosis is a nuclear division that reduces the number of chromosome sets by half to produce haploid gametes, thus maintaining the genetic stability of a species across generations.