What would happen if gametes are formed by mitotic divisions?

If gametes were formed by mitosis, they would remain diploid. Fertilisation would then produce a zygote with double the chromosome number (For humans, instead of 46 chromosomes, the zygote would have 92). The abnormal chromosome number (referred to as polyploidy in animals) would usually be lethal or cause severe developmental defects, thus, leading to genetic instability and formation of non-viable offspring.

Moreover, mitosis does not create genetic variation, so species would lose diversity and adaptability. Therefore, meiosis is essential because it maintains a constant chromosome number across generations and produces genetic variation necessary for survival and evolution.