So let's talk about alternation of generations, which is something that is unique to plants and some produce. So with alternation of generations it's very important that you remember how mitosis and myosis work. So here's a quick review. Mytosis is a type of cell division in which one cell divides and produces two genetically identical daughter cells. So this is what growth and repair is all about. Now myosis is different in that one cell will divide and it will produce a cell or cells but the daughter cells have half the number of chromosomes. Now it's not just any half the number of chromosomes though. In fact we take a diploid cell and go through this process of myosis and we wind up with cells or a cell that is haploid. Diploid cells have two copies of each chromosome whereas haploid cells have only one copy of each chromosome. So alternation of generations uses both mitosis and myosis. Mytosis, one cell divides, produces daughter cells that are genetically identical. Myosis when the cell divides the resulting cell is haploid. So let's look at alternation of generations in more detail and see where the different types of cell division occur. Let's start out with it's a life cycle so where we start is really arbitrary but we'll just start with with the sporo fight generation. Most plants have a dominant sporo fight generation so if you look out your window and you see a bunch of trees and grass then you're looking at the sporo fight generation of plants. So think about an oak tree for example that oak tree represents the sporo fight generation. That sporo fight generation is diploid meaning that it has two copies of each kind of chromosome. Now in the sporo fight generation there are special structures where myosis takes place and when myosis takes place we have a diploid cell that divides by this process of myosis and produces haploid spores. Now what this looks like depends upon the kind of plant that we're dealing with but just in general remember that sporo fights produce spores by myosis. These spores are haploid and so this haploid spore will then divide by the process of myosis and that results in the gameto fight generation and the gameto fight generation of course is haploid. Now sometimes this is confusing because this is the first time that you've probably heard of haploid cells dividing by myosis and producing more haploid cells but remember with myosis one cell divides and produces daughter cells that are genetically identical. So this haploid spore will divide and produce two cells and then those two will divide and then those will divide and those will divide and we'll get a gameto fight. Now in some plants this gameto fight is going to be microscopic and you would never notice it most probably. In other plants such as mosses the gameto fight generation may be dominant but for most plants the gameto fight generation is something that you're not going to be aware of. Now this haploid gameto fight as the name suggests produces gametes sperm and egg. If you think about pollen, pollen represents the male gameto fight for plants such as trees, pine trees oak trees etc. So the sperm and the egg are both haploid. During fertilization the sperm will fertilize the egg and we get a diploid zygote. This diploid zygote will then divide by the process of myosis and we get a spore o fight generation. So this is why it's called alternation of generations and if I drew a line between the across you can see if I can actually make the line work you can see that we alternate between the spore o fight generation and the gameto fight generation.