 We have this family tree over here where we have multiple generations and for some of them we have the full information about genotype and phenotype and others we have gaps and or a complete gap over here and our task is to figure out the missing parts. So to start with I would start with the generation where we know everything about it. So we have one parent that has yellow seeds as phenotype and the genotype has encoded yellow twice and then we have here green seeds and as the phenotype and we also know that the genes have twice the green seeds encoded. Then if you look at their children you see both of their children have yellow seeds. Now given that we know that the genotype of the children is made from one of the alibis of each parent we know the only possibilities here is yellow and green. So one are from let's say the father and one from the mother. So we have overall type here that's definitely a green one from one of the parents and the yellow one of the other one and here the same. There's no other possible combination that can happen. Now we see however that both of them have the phenotype that it's yellow which tells us that the yellow allele is the dominant one over the green one. We could have seen this also from convention that this one was written in capital letters but it's safer to go from what we're actually observing so we're absolutely sure now the yellow one is the dominant one. Now let's go one up. Here this one came from outside so here this one was the child of those two. Both of them have yellow seeds. The fact that they have yellow seed tells us that they must have at least one gene for yellow so each of them has one yellow. And now if you look the child was green so this is only possible if each parent had a green allele of that gene. So this must have been the parents and there was one possible combination where the one green from here got together with the one green from here and then you have two recessive green alleles so that the phenotype actually shows and becomes green. If you look at it at the one up here it's the same as the one down here so what we're going to do in the last generation here we're going to actually try to figure out all possible combinations. To do that we use the so-called punet square it's called square because we're supposed to make a square complicated here to draw and then on one side you write the genotype of one of the parents so here green and here yellow and on the other side you write the phenotype and the genotype of the other parent and now you do the combination so there's one combination green green one green yellow and then here we could have a yellow getting together with the yellow and we could have a yellow with the green so these two are kind of the same thing just reversed order so here what are the possibilities so for the genotype we could have in the end green green so that child would have green seeds then the other possibility would have been that we have green and yellow in this case the yellow is dominant so it would appear to be yellow and then we have the last one yellow yellow where of course also it would appear to be yellow so we have three possibilities now if you look at the genotype what is the probability to have green green if I go up here that is one out of four so that genotype here has a 50 sorry 25 percent chance of happening happening so we know actually the one that happened here that was actually a very lucky draw that only happens one in every fourth now green yellow both of them we have it twice so this one is happening in 50 percent of the cases and then yellow yellow is happening in 35 percent of the cases now interestingly overall if we just look at the phenotype the phenotype yellow will appear in 75 percent of all cases while the one of the recessive one in this case will only appear in 25 percent of the cases so this is a very simplified example how we can use combinations and the punnett square to figure out the family tree of some inheritance of some recessive and dominant traits