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This lesson will examine how a pedigree can be a useful tool in assessing risks of inherited disorders.

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Source: Video and Images Created by Amanda Soderlind

Video Transcription

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Welcome to this lesson on pedigrees. Today, we are going to be identifying how pedigrees can be used to assess risk of inheritance of genetic disorders. So first of all, being able to identify family history is important, because identifying family history allows parents to assess the risk of their child inheriting a genetic disorder if they know a specific genetic disorder runs in the family. So pedigrees are charts that can help to track family history of a particular trait.

So let's say one family has a particular genetic disease that runs in that family. By setting up a pedigree, or this chart, you can track that family history of that particular trait. And geneticists can use this to help to assess the risk of a family member inheriting that trait. So you can kind of see who else in the family has inherited that trait and then assess the risk that another family member is at for inheriting that same trait.

So a carrier is a person who is heterozygous for a recessive trait. So let's use this as an example. Let's say this is representing some sort of trait that runs in the family. Now let's say this person is heterozygous, meaning they have one dominant and one recessive allele. So they are considered a carrier for this disease.

So the reason that they're a carrier is because they show the dominant phenotype. So they have this dominant allele. So the phenotype that they show is dominant. But they are a carrier because they carry or they possess this recessive allele.

Now let's say a certain genetic disease is a recessive disease. So in order to display the phenotype for that disease, you have to have two recessive alleles. OK. So the importance of knowing who is a carrier is that if this person here were to mate with another heterozygous person, their offspring would then have a chance of inheriting this recessive trait.

So if we set up a Punnett square, you can see quick how that works. So if we cross these here, you can see that if this one person who's a carrier mates with another carrier, there's a 25% chance that their offspring will inherit that recessive disease. So it's important to know-- these pedigrees help to identify the risk of a person inheriting these diseases by tracking this family history. So again, a carrier is someone who's heterozygous for a recessive trait. So they carry or they possess that recessive allele that could then be passed on to their offspring.

And a genetic abnormality versus genetic disorder is the next thing that we're going to talk about here. So a genetic abnormality is a trait that a person can inherit that is an abnormal expression of that trait, but it doesn't necessarily cause a health problem. So a genetic abnormality maybe would be that a person has six toes. OK. So it's an abnormal expression of a trait, but it's not going to cause that person any health problems.

Whereas genetic disorder does cause health issues. So an example of a genetic disorder would be sickle cell anemia because it actually does cause health problems versus a genetic abnormality, which does not. So this lesson has been an overview on pedigrees and how pedigrees can be used to track family history and assess the risk of somebody in the family inheriting a certain trait.

Terms to Know

An individual who is carrying a trait genotypically but does not display it phenotypically.

Genetic Abnormality

A genetic characteristic that is not typical (example: 6 toes).

Genetic Disorder

A genetic characteristic that causes health problems (example: Huntingtons Disease).


A chart used to track a trait through a family tree.