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POM Block 2 > 17 Modes of inheritance > Flashcards

17 Modes of inheritance Flashcards

1
Q

How many DNA chromosomes to bacteria usually have?

A

Only 1 (compared to 23 pairs found in humans)

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2
Q

How do bacteria divide?

A

Binary fission (asexual)

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3
Q

Roughly how many genes are encoded by bacterial genomes?

A

4,000-6,000

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4
Q

What does each gene encode for?

A

An mRNA

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5
Q

What does each mRNA encode for?

A

One protein

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6
Q

What does homozygous mean?

A

Two identical copies of an allele for that gene

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7
Q

What does heterozygous mean?

A

Two different alleles for a particular gene

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8
Q

What is a locus?

A

A single position of a gene on the chromosome

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9
Q

How many autosomal pairs do humans have?

A

22

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10
Q

How many chromosomes do humans have?

A

46

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11
Q

Roughly how many genes do humans have?

A

25,000

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12
Q

How many different types of single gene disorders are there?

A

~4,000

Most common ~1/500

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13
Q

What is a dominant autosomal characteristic?

A

A characteristic is dominant if it manifests in a heterozygote

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14
Q

Characteristics of dominant autosomal diseases

A
  • Multiple generations affected
  • Each affected person normally has one affected parent
  • Child of affected person has 1 in 2 chance of being affected
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15
Q

What pattern is seen in dominant autosomal disorders?

A

Vertical pedigree pattern

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16
Q

How many people are affected by Huntington’s disease?

A

1 in 20,000 (UK)

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17
Q

What are the symptoms of Huntington’s disease?

A
  • Start at 30-50 years
  • Difficulty concentrating
  • Depression
  • Stumbling
  • Involuntary jerking
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18
Q

What mutation causes Huntington’s disease?

A

DNA expansion of a CAG repeat on chromosome 4

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19
Q

What does the mutation in Huntington’s cause?

A

Abnormal intracellular Huntington protein aggregate becomes toxic to neurons resulting in cell death

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20
Q

How many people are affected by osteogenesis imperfecta (brittle bone disease)?

A

1 in 15,000

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21
Q

What are some symptoms of osteogenesis imperfecta?

A
  • Bones break easily
  • Mild to severe
  • Hearing loss
  • Breathing problems
  • Short height
22
Q

What causes type I osteogenesis imperfecta?

A

Insufficient quantities of collagen

23
Q

What causes type II, III and IV osteogenesis imeprfecta?

A

An abnormal protein with an altered structure interferes with the function of the normal protein

24
Q

What do dominant autosomal disorders tend to be?

A
  • Gain-of-function (protein with new function made)
  • Dominant negative effect (interference with activity of proteins it binds)
  • Insufficient (1/2 amount of a protein produced, not enough for normal function)
25
Q

What is a carrier?

A

Someone that has lost a single copy of a gene but the normal one is sufficient for normal function

26
Q

What does recessive mean?

A

Two copies of the abnormal gene need to be present for the disease or trait to develop

27
Q

Recessive disorders tend to be…

A

Loss of function mutations (deletions)

28
Q

What pattern is seen in recessive autosomal disorders?

A

Horizontal pedigree pattern

29
Q

How many people are affected by cystic fibrosis?

A

1 in 3,000 newborns

30
Q

What are some symptoms of cystic fibrosis?

A

‘Failure to thrive’

  • Prone to respiratory infections
  • Digestive issues
31
Q

What mutations cause cystic fibrosis?

A

Various mutations in gene encoding chloride ion channel (CFTR gene on chromosome 7)

32
Q

What does the cystic fibrosis mutation cause?

A

Defective chloride ion channel

- Loss of function, degraded faster

33
Q

What highly raises the risk of autosomal recessive diseases?

A

Consanguineous marriages

34
Q

Why are X-linked diseases more impactful on sons?

A

They only have one copy of the X chromosome

35
Q

Give an example of an X-linked recessive disorder where carriers exhibit subtle signs

A

Fabry’s disease

36
Q

Give an example of an X-linked recessive disorder

A

Haemophilia (frequent, severe bleeds -> Factors VIII or IX)

37
Q

Main trend in X-linked recessive disorders

A

All daughters of a man with the disorder will be carriers

38
Q

Main trend in X-linked dominant disorders

A

All daughters and no sons of an affected father are affected

39
Q

Give an example of an X-linked dominant disorder

A

X-linked hypophosphatemia

40
Q

What does X-linked hypophosphatemia cause?

A
  • Kidneys can’t retain phosphate

- Vitamin D resistant rickets

41
Q

What gene mutation causes X-linked hypophosphatemia ?

A

XLH gene mutation resulting in inactivity og PHEX protein

42
Q

Main trends in Y-linked disorders

A
  • Only affects males
  • All sons of affected father
  • Vertical pedigree pattern
43
Q

Example of Y-linked disorder

A

Retinitis Pigmentosa

44
Q

What mutation causes retinitis pigmentosa?

A

Mutation in RPY gene

45
Q

What does the RPY mutation cause?

A

Cells of retina produce a defective protein

46
Q

Key facts about mitochondria

A
  • Share evolutionary past with bacteria

- Have their own DNA (also use proteins encoded by nuclear genes)

47
Q

Main trend in mitochondrial disorders

A

Maternally inherited

48
Q

Why is there a variable phenotypic pattern with mitochondrial disorders?

A

Different cells have different numbers/complements of mitochondria

49
Q

What factors affect the severity of symptoms concerning mitochondrial disorders?

A
  • Amount of WT (wild type) to mutated mtDNA

- Severity of mutation

50
Q

Give an example of a mitochondrial disease

A

Leber’s hereditary optic neuropathy (LHON)

51
Q

What symptoms are common of LHON?

A
  • Visual loss in young adulthood

- Mutations disrupt function of mitochondria (oxidative phosphorylation)

POM Block 2 (9 decks)

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