Hi, this is Tom, and in this episode I'm going to be going through Mendelian Inheritance,

and you can find notes at 0.0.5.com slash inheritance, and in the 0 to Finals Pediatrics book.

And you can find flashcards and questions at members.0 tofinals.com.

So let's jump straight in. Many genetic conditions exhibit a simple inheritance pattern called

Mendelian Inheritance. This type of inheritance only occurs when the disease is caused by a single abnormal gene

on one of the autosomes, not the X or Y sex chromosomes. Huntington's disease and cystic fibrosis

are examples of diseases with Mendelian inheritance. The allele coding for Huntington's disease is

dominant. To develop the phenotype for Huntington's disease, meaning to actually have the

disease, only a single copy of the disease allele is required.

Huntington's disease is autosomal dominant.

The allele coding for cystic fibrosis is recessive.

To have the phenotype for cystic fibrosis,

meaning to actually have cystic fibrosis, both copies of the gene must be the

disease allele. When there is one copy of the disease allele and one normal copy of the gene,

the person is described as a carrier. They don't have the disease, but they do carry the abnormal

gene. This means they can pass on the disease, but they do carry the abnormal gene.

This means they can pass on the disease allele to their offspring.

The normal copy of the gene overrides the abnormal copy.

Cystic fibrosis is autosomal recessive.

Let's go through how to calculate the risk of inheriting an autosomal recessive. Let's go through how to calculate the risk of inheriting an autosomal recessive condition. A common exam scenario test your ability to calculate the risk of passing a genetic

condition onto a child. By calculating the four possible outcomes for each scenario, you should always be able to calculate

the risk.

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