Question

What would the human life cycle be like if we had alternation of generations? Assume that the multicellular diploid stage would be similar in form to an adult human.

Answer 1

Alternation of generation is also called metagenesis, in it there is an alternation of sexual phase and asexual phase in the life cycle of an organism. The asexual and sexual phase are morphologically and chromosomally different.

For sexually reproducing individuals it is required that the diploid cells should divide by mitosis to produce haploid cells, and haploid cells fuse to form a diploid new organism.

In plants and animals or humans the alternation of generation differs. In plants diploid and haploid organisms are multicellular but in humans diploid or adult humans ( male or female) are multicellular, but they produce in male haploid sperm cells and in case of females a haploid egg cell, both the haploid cells fuse to form a diploid cell and form an adult human being having 2n number of chromosomes.

In Plants an entire generation is either haploid or diploid but in humans the haploid phase is for a short period of time.

If alternation of generation were found in humans then,  the multicellular diploid stage of the life cycle will not produce gametes. Rather both males and females will produce haploid spores by meiosis. These spores will give rise to multicellular male and female haploid stages. The multicellular haploid stages will produce gametes and reproduce sexually. An individual at the multicellular haploid stage of the human life cycle may look like adult human beings, or it may look completely different.