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Pedigrees

Pedigrees

Description:

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

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Tutorial

What's Covered

This lesson will cover the use of pedigrees by looking at:

  1. Pedigrees
  2. Genetic Abnormality vs. Genetic Disorder

1. Pedigrees

Being able to identify family history is important because it allows parents to assess the risk of their child inheriting a genetic disorder that runs in the family. Pedigrees are charts that can help to track family history of a particular trait.

A carrier is a person who is heterozygous for a recessive trait, meaning they have one dominant and one recessive allele. If this recessive trait is for a disease, then they are considered a carrier for it. This person only expresses the dominant phenotype, but they still possess the recessive allele. In order to display the phenotype for that disease, someone would have to have two recessive alleles. The importance of knowing who is a carrier is if this person were to mate with another heterozygous person, their offspring would then have a chance of inheriting this recessive trait.

Terms to Know

    • Pedigree
    • A chart used to track a trait through a family tree.
    • Carrier
    • An individual who is carrying a trait genotypically but does not display it phenotypically.
IN CONTEXT

What are the odds two heterozygous parents would have an offspring that expresses only the recessive trait? How would you find this out?

To determine what the chances are, you would need to use a Punnett square:

resessivepunnet.png

If you cross two heterozygous people, the square shows there is a 25% chance that their offspring will inherit that recessive trait.



2. Genetic Abnormality vs. Genetic Disorder

A genetic abnormality is a trait that a person can inherit that is an abnormal expression of that trait, but doesn't necessarily cause a health problem.

ExampleA person that has six toes. It is an abnormal expression of a trait, but it's not going to cause that person any health problems.

A genetic disorder, on the other hand, does cause health issues.

ExampleSickle-cell anemia is a genetic disorder because it actually does cause health problems

Term to Know

    • Genetic Abnormality
    • A genetic characteristic that is not typical (example: 6 toes).
    • Genetic Disorder
    • A genetic characteristic that causes health problems (example: Huntingtons Disease).

Summary

Pedigrees are used to track the family history of a particular trait. This is useful in determining if someone is a carrier for a trait like a recessive disease. If they are, and they have offspring with another heterozygous person for that trait, their offspring will have a chance of expressing that recessive trait. Genetic abnormalities are abnormal traits a person can inherit that do not cause health problems, while genetic disorders are inherited traits that do cause health problems.

Keep up the learning and have a great day!

Source: This work is adapted from Sophia author Amanda Soderlind.

TERMS TO KNOW
  • Genetic Disorder

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

  • Genetic Abnormality

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

  • Carrier

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

  • Pedigree

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