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Skip to 0 minutes and 14 secondsThis short video will show you how to draw a pedigree or family tree. When we're drawing a family tree, we use a variety of symbols. You can see these symbols outlined here. We can represent someone as a male by drawing a square or as a female by drawing a circle. If somebody has died, a diagonal line is drawn through either the square or the circle. And if someone is affected with a genetic condition, we shade in that square or circle as you can see here. If someone is a carrier of a condition but not actually affected by it, then we show that by shading half in the circle or the square.

Skip to 1 minute and 5 secondsIn genetics, we use a term which is the consultand, and this refers to the person sitting in front of you in the clinic asking for advice. And we mark them by drawing a C beside their name.

Skip to 1 minute and 21 secondsNow, when it comes to the actual setup of the pedigree, we'll see some examples in the following slides. But the basic idea is outlined here. So this square here is a male. And we can see that he is joined to his partner by a horizontal line. A vertical line is then drawn down from the middle of the partnership, and a second horizontal line is drawn from which various vertical lines come down for each child. Traditionally, we draw the oldest child on the left and work our way along to the right. So you can see this person here has two sons.

Skip to 2 minutes and 8 secondsIf a partnership ends, for example in divorce, we draw a diagonal line through the horizontal bar. If somebody then remarries or has another partner, we can then add them on to the other side. Obviously the children may come from either partnership, so it's important to show this clearly on the pedigree.

Skip to 2 minutes and 33 secondsA pregnancy is represented by a diamond shape. And you would always draw the gestation, if you knew it, on the pedigree as well. 11 out of 52 means 11 weeks of gestation. One further symbol that I've shown here is twins, either non-identical or identical. And you can see that the basic shape is the same. Instead of one child coming down from a vertical bar, you have two children. If they are identical, there is another bar drawn between them. And if they're non-identical, we don't include this. There are a vast array of other symbols, but these are the main ones that you would need for drawing a basic family tree.

Skip to 3 minutes and 21 secondsSo in the next couple of slides, we'll look at what a family tree might look like.

Skip to 3 minutes and 31 secondsOK so here is a simple three-generation family tree. Now, you can see that I have shaded some people in, so they're obviously affected by a particular genetic condition. I have drawn generation numbers. So this is generation one. This here is generation two, and this is generation three. The people are then numbered one and two from left to right, and you can see the same thing in the following generation and also in the third generation.

Skip to 4 minutes and 15 secondsYou can see that the couple in the first generation have had one, two, three children, of whom two seem to be affected by the genetic condition present in the father.

Skip to 4 minutes and 34 secondsThis individual here, II:3, has married II:2, and they have three children, a boy, a boy, and then a girl. And it seems that the first male child and the female child are affected by the genetic condition. What's missing from this family tree is a lot of the basic information such as names and ages. So we'll look in a bit more detail at that in the next slide.

Skip to 5 minutes and 11 secondsIf we look at this second family tree, we can see that we're told quite a lot more information. This is a four-generation family tree, generation one, two, three, and four. And we can see that the consultand is an individual called Jennifer. She has had breast cancer at age 30 years. Working back through the family, we can see that her father is age 60 and her mother is age 63. Her father has an elder sister who has died and who was affected with ovarian cancer at age 45 years and died a year later. If we go back a further generation to generation two, we can see that the parents of these individuals--

Skip to 6 minutes and 6 secondsIII:1 and III:2-- one of them died in a road traffic accident age 45 years, this individual here. She had a sister who died aged 48 years and who was affected with bilateral breast cancer.

Skip to 6 minutes and 28 secondsGoing back one further generation, we see another individual affected with breast cancer, someone who died aged 45 years. You'll see in the next article how important these features are and how they might help us to determine whether or not there is an inherited mutation that's causing the breast cancer in this family. You'll also get the opportunity to practise drawing a family tree from information that we give you. So hopefully during this short section you'll be able to see the importance of genetics in determining whether or not a cancer in a family may be inherited.

Drawing a family tree

In this video Dr Leah Marks introduces the symbols required to draw a family tree.

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This video is from the free online course:

Cancer in the 21st Century: the Genomic Revolution

University of Glasgow