Below are the principal symbols used when drawing a pedigree. Once phenotypic data is collected from several generations and the pedigree is drawn, careful analysis will allow you to determine whether the trait is dominant or recessive.
Here are some rules to follow. It shows how individuals within a family are related to each other. We can also indicate which individuals have a particular trait or genetic condition.
If we take a pedigree, which we usually try to include at least three generations, we might be able to determine how a particular trait is inherited. Using that information, we might be able to tell the chance that a given individual will have the trait themselves or could pass it on to their children. There are standard ways to draw pedigrees so that we can all look at a pedigree and understand it.
This male right over here does have freckles. But once again, this phenotype, that's the observed characteristic, we don't know exactly the genotype just from this. Although we might be able to infer some ideas about the genotype by seeing how the phenotype patterns spread from generation to generation. But just going back to understanding the pedigree itself. When you have a horizontal line connecting a male and a female, it's called a marriage line. And it means that they are coupling up and they are reproducing.
They don't necessarily, I guess, have to be married. It's more that they reproduce. So this male and this female have reproduced. And then this vertical line that goes from that horizontal line, that's known as the line of descent.
So it's going from that first generation to the second generation. And so all of the people connected to that vertical line at the bottom of the vertical line, these are their children. All the people who are directly connected to this. And this is known as a sibling line.
So, this person, this person and that person, they are all brothers and sisters. You can see that generation one, they had two daughters, one of whom exhibited freckles, and one son, who had freckles. Now these other people in generation two, these aren't children of the first generation. These are people, you could say, who are brought into the family. They either married into the family, or you could just say they reproduced with the children.
But that's what's happening with generation two. And so you can see, you have another what's known as a marriage line, but I guess it could be a coupling line, a line of descent, and then they have two daughters in this case. So it turns out that freckles is an autosomal dominant trait. Childhood Cancer Genomics. Study Findings. Metastatic Cancer Research.
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