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Hi today we're going to talk about family trees in biology we call a family tree a pedigree chart so let's take a look at what the symbols mean when we're trying to represent who's related to who males are usually represented by squares on a pedigree chart and females are presented by circles if the circles are empty this means that persons not carrying the trait that we're looking for if the circles are filled in or the squares are filled in this means that this person carries a trait that we're looking at say we're looking at hemophilia this person would be carrying he would have hemophilia and so with this person we can also show that someone's carrying a trait but doesn't actually have that particular shape by shading in half of their circle or their square we call these people carriers they're not they don't have whatever gene we're looking for but they're carrying it and they may give it to the next generation of children relationships on family trees are indicated by lines a horizontal line between a male and a female indicates that those two people are married if you look to the right you'll see that over here we have two people who are married and then we have a bracket that represents their children they have two girls and one boy as represented by the circles and the square you'll also notice that there's Roman numerals off to the right Roman numeral one means that these are the parents they're the first generation and Roman numeral two means that these are the children that they're the second generation we can show many generations on a family tree if we keep going here's an example of a family tree so we have Mary who's married to Carlos they have three children Jose Alex and Lucy Lucy gets married to Steve and together they have two children Hannah and Brenda so that's how you make a family tree it's pretty easy when you think about it so how do we tell if traits are dominant or recessive on a family tree you could write out a genotype for every single person on the family tree and that's certainly possible but for now we're going to look at some general patterns if you look at this one on the left this pedigree has three generations somebody in every generation is affected by the trait that we're looking for so that means this tree is probably going to be a dominant trait as it shows up every generation that we have children on the other hand they look on the chart on the right we'll see that we have somebody affected in the first generation but no one is affected in the second generation and then the trait shows up again in the third generation so this trait skips a generation we can probably assume that this trait is recessive because it doesn't show up all the time last we have to see if these trades might be sex linked or if they're autosomal traits an autosome is just a body chromosome and X the sex linked chromosomes would be the X and the y so let's take a look the one on the left we can see that all the squares are shaded...