gametes (egg cells and sperm cells) are haploid so they only have half the amount of DNA of a body cell. Specifically, these cells only have one copy of each chromosome, while body cells have two copies of each chromosome. Why would it be a problem if gametes were diploid?
If gametes were diploid rather than haploid, it would result in an incorrect number of chromosomes in the resulting zygote after fertilization. When two haploid gametes (one from each parent) combine during fertilization, they create a diploid zygote which then goes on to develop into a multi-celled organism.
If the gametes were already diploid, the zygote would end up with double the normal number of chromosomes, leading to a condition called polyploidy. Polyploidy can cause severe developmental abnormalities and is typically lethal in animals. It can also result in reduced fertility or sterility in plants.
Therefore, the haploid nature of gametes is crucial for maintaining the proper chromosome number and genetic balance in offspring.