Genetic Inheritance Flashcards

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1
Q

What does mitochondrial DNA code for.

How is it inherited?

A

Codes for 15 proteins, rRNA, some tRNA
most encoded by genome, small amount by mitochondria itself

From mother

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2
Q

What is Dominant autosomal inheritance?

A

Dominant characteristic will manifest as phenotype in a heterozygote.

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3
Q

Why are brown eyes dominant?

A

Gene responsible -
OCA-2

It controls the amount of melanin in melanocytes.

Active OCA-2 leads to melanin build up

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4
Q

What is the chance of dominant autosomal disorders affecting offspring?

A

1/2

vertical pedigree pattern

Can be gain of function, dominant negative effect, insufficient

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5
Q

What are the symptoms of Huntington’s disease?

What mutation is it due to?

A

( Dominant )
Start age 30-50

Difficulty concentrating, depression, stumbling, involuntary jerking, problems swallowing

Due to DNA expansion of CAG repeat on chromosome 4 resulting in protein aggregation and causes neuronal function issues - toxic to neurons

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6
Q

What are the symptoms of Osteogenesis imperfecta?

What mutations can it be caused by?

A

( Dominant )

Bones break easily, hearing loss, breathing problems, short height, blue tinge to whites of eyes

Type I - insufficient collagen
Type II,II,IV - abnormal protein with altered structure interferes with function of normal protein

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7
Q

Why are carriers of Autosomal Recessive disorders unaffected?

A

They have lost a single copy of a gene but the normal one is sufficient to maintain normal function

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8
Q

Each subsequent sibling of an autosomal recessive disorder child has a (a) chance of being affected?

A

1/4

horizontal pedigree pattern

both parents have to be carriers

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9
Q

What are the symptoms of Cystic Fibrosis?

What makes the characteristic of the disorder recessive?

A

Failure to thrive
Defective chloride ion channel
Impaired airway defence
Digestive issues

Chloride ion channel mutations - CFTR gene on chromosome 7.
Need both copies to result it complete mutant CFTR channels

Loss of function affect

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10
Q

How many genes make up the X and Y chromosome and how many proteins can each code respectively?

A

1000-1300 genes, code for 850 proteins

150 genes, code for 50-70 proteins

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11
Q

Who do X-linked disorders effect? (recessive)

A

Mainly males, effectively dominant to them as one gene on X chromosome will show trait.

Females who are homozygous will also have condition

Parents and children to affected ppl are normally unaffected

example - haemophilia - different levels of severity, in some diseases females can give subtle signs of the disease as carriers e.g. fabrys

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12
Q
( X linked recessive ) 
brothers of an affected son have (a) chance of (b)
Sisters have (c) chance of (d)
A

a - 1/2

b - having disorder

c - 1/2

d - being a carrier

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13
Q

If a father has an X-linked recessive disorder, what will his son or daughter have?

A

Son will be healthy as they only inherit Y from father not X which trait is on.

Daughters will all be carriers as they will inherit the X from the father.

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14
Q

If a father has an X-linked dominant disorder, what will his son or daughter have?

A

All daughters but no sons will be affected. Conditions often milder and more variable in females.

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15
Q

How do we know Hypophosphatemia is a Dominant X linked disorder?

A

PHEX gene mutation
overproduction of FGF21 which inhibits kidney phosphate resorption. Results in VD resistance rickets

X linked because of overproduction characteristic. We cannot counter that with a normal gene

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16
Q

What patterns are seen in Y-linked disorders?

Example

A

Affects only males, all sons of affected father affected

E.g. Retinitis Pigmentosa, mutation in RPY gene : cells of retina produce defective protein

17
Q

How many children of a mitochondrial inherited disorder affected women may be affected?

A

All may be affected, extremely variable

18
Q

Why are mitochondrial diseases so variable?

A

Have multiple copies of genome, some normal some mutant.

Heteroplasmy

Disease will only be expressed when a threshold is passed.

Mitochondria replicate through binary fission and so can lose or gain mutated genes

19
Q

Are all mitochondrial diseases caused by mutations in mDNA?

A

most are caused by mutations in nuclear genome and have mendalian or sex chromosome linked inheritance

20
Q

Why may mitochondrial disease develop with age?

A

Number of affected mitochondrion in certain cells may develop with age and accumulate

21
Q

Symptoms of mitochondrial disease characteristics?

Examples

A

Unrelated multi system symptoms

E.g. Leber’s hereditary optic neuropathy
- visual loss in young adults, typically males

22
Q

Genetic inheritance extra info?

A

25,000 genes

22 autosomal pairs

  • single gene disorders most common 1/500 , then chromosomal disorders 1/150 live births, complex disorders common due to genetic and environmental factors