parturition. Note that the first milk produced immediately after

7. 
   Oxytocin, which is the hormone that induce uterine contraction and triggering the series of changes associated with labor and subsequently, parturition. Sometimes it can be administered to induce labor in pregnant women whose expected date of delivery has been exceeded and are due for delivery
   

The autonomic nervous system also plays important roles in the reproductive chain e.g. in males where by:

1. 
   The physiological penile erection prior to copulation is under the influence of the parasympathetic nervous system, and
   

2. 
   The physiological release of semen-containing spermatozoon termed ejaculation is under the influence of the sympathetic nervous system.
   

It should be noted that usually, gametes have a haploid number of chromosomes (23), with a genetic constitution determined during meiotic division, at the stage termed “crossing over” (genetic recombination). It is known also, that no two daughter cells have same genetic constitution and this forms one of basis for human variation.

After fertilization (between the male and female gametes), the resultant cell called Zygote, has a diploid number of chromosome (46) comprising 23 chromosomes from the male and female gametes respectively. As such, the zygote has a genetic constitution that is not exactly same with those of any of the parents. This also contributes to human variation.

In embryology, genetic anomalies (e.g. non-disjunction of chromosome, deletions etc.), accounts for some of the documented congenital anomalies. Some genetic anomalies may arise due to mutations following exposure to radiations or other related factors capable of inducing inheritable gene mutation.

Furthermore, genes play significant roles in embryonic induction and apoptosis.