Pedigree Flashcards

1
Q

What is pedigree?

A

Visual representation of a family
- Used to study single gene disorders

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2
Q

If both parents are carriers of a AR gene what are the chances of the child being being homozygous recessive (affected by disease)?

A

25%

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3
Q

If the mother comes from a population with a 1/50 chance of being a carrier of disease and the father a 1/100 what are the chances that both parents are carriers?

A

(1/50) * (1/100) = 1/5,000

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4
Q

If the mother comes from a population with a 1/50 chance of being a carrier of a Recessive disease and the father a 1/100 what are the chances that there child will be affected by the AR disease?

A

(1/50) * (1/100) = 1/5,000

(1/5000) * (1/4) = 1/20,000

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5
Q

Why are X-linked dominant genes never passed through the male line?

A

Male only passes y chromosome

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6
Q

In an aut dominant disease if there is one affected parent what percentage of offpsring will have the disease?

A

50%

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7
Q

What is Incomplete dominance?

A

Aut dom disease where the heteroztgote phenotype is different (less severe) than the homozygote (more severe)
- E.g familial hypercholesterolemia and achondroplasia

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8
Q

What is an example of a disease with incomplete dominance, where in homozygote individuals it is fatal?

A

Achondroplasia
- In heterozygotes it causes dwarfism

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9
Q

Why in X-linked disorders are males always affected (whether it is dominant or recessive)?

A

They only have one X chromosome

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10
Q

How can a X-linked recessive disorder be identified?

A

All males with gene will be affected
- No females affected (usually)
- No male to male transmission

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11
Q

How can a X-linked dominant disorder be identified?

A

All males with gene will be affected and will have it transmitted through the mother’s side
- Females will be affected
- Affected father MUST give diseased X chromosome to daughter
- NO male to male transmission, affected father will NOT pass disease to son

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12
Q

What percentage of sons of heterozygous mothers with an AR allele will be affected by disease?

A

50%

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13
Q

What are the 2 ways a female may develop an X-linked recessive gene?

A
  • If homozygous for gene (father affected and mother a carrier)
  • Skewed lionization
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14
Q

What is lyonization?

A

Inactivated of X chromosome in females

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15
Q

What is the lyonized X chromosome known as?

A

Barr body

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16
Q

How is the X chromosome lyonized or inactivated?

A

Condensed into heterochromatin w. methylated DNA

17
Q

When does lyonization occur?

A

Early in development
- Embryo <100 cells

18
Q

What does lyonization result in?

A

Mosaicism
- Different inactive X chromosomes in different cells as it is a random process

19
Q

How can you differentiate an X-linked dominant disorder from an Aut Dom pattern?

A

No male-male transmission in X-linked disease
- Father always passes Y chromosome

20
Q

Whaty is the second most common cause of intellectual disability?

A

Fragile X syndrome

21
Q

What are the features of fragile X syndrome?

A
  • Long, narrow face, large eears and jaw
  • Features of autism
  • More severe in males
22
Q

What organs are most affected by mitochondrial gene mutations?

A
  • CNS
  • Skeletal muscle
    Both heavily rely on aerobic metabolism
23
Q

A mixture of abnormal and normal genes in mitochondria is known as what?

A

Heteroplasmy

24
Q

What does the mutant gene expression levels depend on?

A
  • Amount of normal vs abnormal genes
  • Number of mutant mitochondria in each cell/tissue
25
What is the difference beetween a homoplasmic and heteroplasmic mother?
Homoplasmic mothers - All children have mutation Heteroplasmic - Variable
26
Why may not all children display disease if their mother has a mitochondrial disease?
Mother may be heteroplasmic
27
What are the 3 classic signs of mitochondrial myopathies?
- Weakness - Confusion - Lactic acidosis
28
Wwhat is the classic sign of mitochondrial myopathy on biopsy?
Red ragged fibres - compensatory proliferation of mitochondria which accumulate and appear bright red on blue background
29
Multifactorial inheritance is what?
Genes, lifestyle and environemnt contributing toward disease
30
What is polygenic inheritence?
inheritance of a trait governed by more than one genes