Typical and Atypical Mendelian Inheritance Flashcards Preview

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Flashcards in Typical and Atypical Mendelian Inheritance Deck (22)
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What are the 4 types of typical Mendelian inheritance?

Autosomal dominant
Autosomal recessive
X-linked dominant
X-linked recessive


What are the 4 types of atypical Mendelian inheritance?

Genetic anticipation
Pseudo-dominant inheritance
Mitochondrial inheritance
Pseudo-autosomal inheritance


Give 4 examples of autosomal dominant disorders.

Hereditary breast/colon cancer
Autosomal dominant polycystic kidney disease (ADPKD)
Neurofibromatosis type 1 (NF1)


List 3 features of autosomal dominant inheritance on family trees.

Vertical transmission pattern (i.e. every generation is affected)

Males and females equally affected

Father-son transmission


What is variable expression?

What causes it?

Give 1 example of this.

AD conditions in which individuals within the same family can be affected to different extents

CAUSED BY: modifier genes

EXAMPLE: FGFR2 gene in BRCA2 mutations


How do you tell the difference between autosomal and X-linked dominant disorders?

The two can look very similar.

Father-son transmission

Autosomal: present

X-linked: not possible, because fathers pass on Y chromosome to sons


List 4 other features of autosomal dominant disorders.

Give a brief description of each.

Variable expression
-Caused by modifier genes
-Individuals within the same family can be affected to different extents

Incomplete penetrance
-Caused by modifier genes
-Individuals who are unaffected due to incomplete penetrance can still pass on the mutation and have affected children

Complete penetrance
-Mutation will definitely cause disease
-E.g. achondroplasia

Gonadal mosaicism
-Caused by new mutations in some egg/sperm cells in unaffected individuals
-These (unaffected) parents will have a slightly higher risk of having affected children


Give 5 examples of autosomal recessive disorders.

Sickle cell anaemia
Cystic fibrosis
Phenylketonuria (PKU)
Spinal muscular atrophy (SMA)
Congenital adrenal hyperplasia (CAH)


List 3 features of autosomal recessive disorders on family trees.

Horizontal patterns (i.e. affected individuals within same generation)

Males and females affected equally



List 3 other features associated with autosomal recessive disorders.

Give a brief description of each.

-Heterozygous individuals carrying one affected gene, which isn't enough to cause disease

Compound heterozygotes
-There are 2 mutated alleles, but each allele contains a different mutation

Complete penetrance
-If the mutations are present, the individual will always have the disease


Give 2 examples of X-linked recessive disorders.

Duchenne muscular dystrophy (DMD)
Becker's muscular dystrophy (BMD)


List 4 features of X-linked recessive disorders on family trees.

Knights move pattern (affected males and affected uncles)

No male-male inheritance

Mostly (or only) males affected

Manifesting carriers


What are manifesting carriers?

What is the cause of this?

Female carriers who present with an X-linked recessive disorder, despite only having 1 mutated X chromosome.

Caused by: skewed X inactivation (i.e. too many health X chromosomes are inactivated)


List 3 examples of X-linked dominant disorders.

Which of these are always fatal for males?

Vitamin D resistant rickets

Incontinentia pigmenti (male lethality)

Rett syndrome (male lethality)


List 3 features of X-linked dominant disorders on family trees.

Vertical pattern

Mostly females affected

No male-male transmission


Give 3 examples of disorders showing genetic anticipation.

Huntington's disease
Fragile X syndrome
Myotonic dystrophy


Give 1 example of a disorder with pseudo-dominant inheritance.

What is the carrier frequency for this disorder?

Gilbert's syndrome (carrier frequency 50-60%)


Give 1 example of mitochondrial inheritance.

Leigh syndrome


List 2 features of disorders with mitochondrial inheritance.

Variable expression

Only inherited from mother (because egg cell passes on mitochondria, sperm cell does not)


Define "pseudo-autosomal inheritance".

X-linked inheritance which appears as an autosomal dominant condition, due to the fact that the mutation is found on a region of the X chromosome that is commonly joined onto the Y chromosome (a pseudo-autosomal region, PAR1 or PAR2)


Give 1 example of a disorder caused by pseudo-autosomal inheritance.

Leri-Weill dyschondrosteosis


Describe the pathophysiology of pseudo-autosomal inheritance. (2)

1. The PAR1 and PAR2 regions of the X chromosome frequently attach to the Y chromosome (i.e. undergo recombination)
-This is NORMAL

2. When there is a mutation in PAR1 or PAR2, this mutation will be inherited in a way that appears autosomal, due to the fact that it is on both the X and Y chromosome