Final answer:
The fertilized egg, or zygote, contains two sets of genetic information, one from each parent. A total of 46 chromosomes are present in the zygote, making it diploid. This genetic contribution determines the offspring's phenotype.
Step-by-step explanation:
The fertilized egg, or zygote, contains two sets of genetic information. This comes from the process of fertilization where one sperm cell (haploid) and one egg cell (haploid) combine their genetic material. The sperm and egg each carry 23 chromosomes, for a total of 46 when they join. As a result, the zygote becomes diploid, meaning it has two complete sets of chromosomes, with one set inherited from each parent. These paired chromosomes will dictate the genetic characteristics, known as the phenotype, of the offspring.
Interestingly, in the rare case of fraternal (dizygotic) twins, two separate eggs are fertilized by two different sperm, leading to the development of two genetically unique siblings. Nonetheless, each twin's zygote still retains the standard two sets of chromosomes from their respective parental contributions.