Unit 4: Single-gene Diseases (Mendelian Disorders)

These flashcards cover key vocabulary terms and definitions related to single-gene diseases and Mendelian disorders.

Mendelian Disorders

Genetic disorders caused by mutations in a single gene.

Single-gene disordered or monogenic disorders caused by mutations in genes in the nuclear genome

Single-gene disorders are called Mendelian because they occur on average in fixed proportions among the offspring of specific types of mattings 

Rare disease

A disease affecting fewer than 200,000 people in the US.

Although individually rare, they are collectively common

Large number of rare disorders are caused by mutations that alter the function of single genes 

Currently there are at least 7000 disorders have been identified 

Monogenic disorders

Single-gene disorders caused by mutations in nuclear genome genes.

Law of Segregation

Mendel's law stating that alleles segregate from each other during gamete formation.

Law of Independent Assortment

Mendel's law stating that genes for different traits assort independently during gamete formation.

Dominant disorder (trait)

A genetic disorder that manifests in heterozygotes.

When human monogenic disorders is determined by a nuclear gene, and it is manifested in the heterozygote 

Recessive disorder (trait)

A genetic disorder that manifests only in homozygotes.

When human monogenic disorders is determined by a nuclear gene and it is manifested in the homozygote, but NOT the heterozygote 

Pedigree

A graphical representation of a family tree used to analyze inheritance patterns using standard symbols 

It is one of the most commonly used tools in medical genetics 

Proband

The first family member affected by a genetic disorder and identified by a geneticist.

Consultand

The person seeking genetic consultation, who may be affected or unaffected.

Consanguinity

Marriage or reproduction between individuals who are closely related. (Inbreeding)

Couples who have one or more ancestors in common are consanguineous 

Autosomal recessive inheritance

A pattern where two unaffected parents can have affected children due to both being carriers.

Horizontal pattern in a pedigree

Occurrence of the disorder only in one generation.

Allelic heterogeneity

Different mutations within the same gene can cause the same disorder.

Tay-Sachs disease

A tragic degenerative condition caused by a mutation in Hexosaminidase A, leading to CNS deterioration.

Sickle cell anemia

An autosomal recessive condition caused by a mutation in the beta-globin gene, leading to distorted red blood cells.

Genetic isolate

A population with a higher frequency of certain rare recessive genes compared to the general population.

Mendel’s Laws

1. The Law of Segregation

2. The Law of Independent Assortment

How do we study single-gene disorders?

in humans, single-gene disorders are recognized by their patterns in in transmission in families 

1. Genetic analysis in humans is observational and indirect rather than experimental

2. To establish the pattern of transmission, we first collect information about the patients family history and summarize the details in the form of a pedigree

3. Once the pedigree is constructed, the information in the pedigree will indicate how the trait is inherited and which family members are at risk