What is the outcome of fertilization in terms of chromosome number?

The outcome of fertilization in terms of chromosome number is the formation of a diploid zygote. This process begins when a sperm cell, which carries a haploid set of chromosomes (one half of the species' chromosome complement), fuses with an egg cell, also haploid. Upon fertilization, the genetic material from both gametes combines, resulting in a single cell – the zygote – that contains two complete sets of chromosomes, one from each parent. This diploid state restores the normal chromosome number for the species and is crucial for proper development.

The other options refer to different chromosome configurations that do not occur as a direct result of typical fertilization. For instance, haploid cell formation would refer to the gametes themselves before fertilization takes place. Triploid and tetraploid formations can occur in certain circumstances, such as in polyploid species or through abnormal fertilization processes, but they are not the normative outcome of the fertilization process.