Roof rats are the worst rodent pest in the state of Florida and most abundant. The Norway rat (Rattus norvegicus) that is familiar to most people is rare in Florida. Roof rats consume and destroy stored animal and human food, attack fruit crops, and take up residence in attics, soffits, hollow walls, and out-buildings.
1 The sperm brings in another 23 chromosomes to complement the 23 held in the egg to get to a total of 46 chromosomes - what all of us normal people have.  We know from in vitro fertilization studies that the egg is only capable of being fertilized for about 24 hours after ovulation.
After fertilization, it can take 5-10 days for the fertilized egg to begin to attach itself to the lining of the uterus. Pregnancy begins when this happens. It is true that conception is the same moment as fertilization. However, sperm will attempt to fertilize an egg at any opportunity they get.