Lecture 7: Human Pedigrees Flashcards

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1
Q

How many diseases following Mendelian inheritance patterns are there?

A

≈ 7300, numerous but rare.

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2
Q

What are some examples of Mendelian genetic diseases?

A

Sickle cell anaemia

Cystic fibrosis

Achondroplasia

Marfan syndrome

Haemophilia

Huntington’s disease

Albinism

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3
Q

What is a human pedigree chart?

A

A chart that diagrams the inheritance of a trait or health condition through generations of a family.

They help to determine how the disease is inherited and the probability of its prevalence in offspring.

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4
Q

Describe the characteristics of an autosomal recessive disorder.

A

• Appears in the progeny of unaffected parents.

• Affected progeny includes both males and females.

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5
Q

What are some examples of autosomal recessive disorders?

A

Albinism

Cystic fibrosis

Sickle cell anaemia

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6
Q

State the characteristics of pedigrees of autosomal dominant disorders.

A

• Show affected males and females in each generation (every affected individual must have one affected parent).

• Show affected men and women transmitting the condition to equal proportions of their sons and daughters.

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7
Q

What are some examples of Mendelian autosomal dominant disorders?

A

Pseudoachondroplasia

Huntington’s disease

Marfan syndrome

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8
Q

What are some diseases caused by X-linked disorders?

A

Colour blindness

Haemophilia A

Duchenne muscular dystrophy

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9
Q

What are the characteristics of an X-linked recessive disorder?

A

• Strong skew towards males being affected.

• Also compatible with an autosomal recessive pattern of inheritance.

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10
Q

Define the characteristics of X-linked dominant disorder.

A

Only females are affected in generation II.

• Chart is also compatible with autosomal dominant inheritance.

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11
Q

State why are there differences in dominant & recessive X-linked and autosomal disorders? What are they?

A

Due to males having only one X chromosome, the inheritance patterns are different between X-linked and autosomal disorders.

• In X-linked recessive disorders males are much more likely to be affected as they only need to inherit one faulty copy, while females can be carriers.

• In X-linked dominant disorders, affected males will only transmit the conditions to daughters, but affected females will transmit the condition equally to their sons and daughters.

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12
Q

What is the probability of a non-affected sibling in a dominant disorder being a carrier?

A

0, if they are non-affected and is a dominant disorder it cannot carry the mutant allele.

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13
Q

What is the probability of a non-affected sibling in an autosomal recessive disorder being a carrier?

A

2/3, as they do not have the disorder they must be either AA or Aa.

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14
Q

What is the probability of a non-affected female with an affected brother being a carrier in an X-linked recessive disorder? (Assume her brother is the only affected individual of this pedigree).

A

1/2, mother is an obligate carrier. Daughter has 50% chance of inheriting the mutant X.

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15
Q

What is the probability of inheriting the mutant gene from an obligate carrier in an X-linked recessive disorder?

A

1/2, carrier must be female as X-linked. Chance of passing each chromosome is 50/50.

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16
Q

What is the probability of inheriting the mutant gene from an unaffected parent in a dominant disorder?

A

0, by definition, a non-affected parent cannot carry the mutant allele in a dominant disorder.