Lower-class people experience a wide array of health problems as a result of their economic status. They are unable to use health care as often and when they do it is of lower quality, even though they generally tend to experience a much higher rate of health issues. Lower-class families have higher rates of infant mortality , cancer , cardiovascular disease and disabling physical injuries. Additionally, poor people tend to work in much more hazardous conditions, yet generally have much less (if any) health insurance provided for them, as compared to middle- and upper-class workers. 
Fertilization is the process by which a sperm combines with an oocyte, or egg cell, to produce a fertilized zygote. The sperm released during ejaculation must first swim through the vagina and uterus and into the fallopian tubes where they may find an oocyte. After encountering the oocyte, sperm next have to penetrate the outer corona radiata and zona pellucida layers of the oocyte. Sperm contain enzymes in the acrosome region of the head that allow them to penetrate these layers. After penetrating the interior of the oocyte, the nuclei of these haploid cells fuse to form a diploid cell known as a zygote. The zygote cell begins cell division to form an embryo.