A reproductive cell having the haploid number of chromosomes, especially a mature sperm or egg capable of fusing with a gamete of the opposite sex to produce the fertilized egg .

• 在哺乳动物中,卵与精子结合而成受精卵,受精卵发生数次细胞分裂(卵裂)后,形成一个中空球形的囊胚。