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Modes of Inheritance Flashcards

1
Q

Features of autosomal dominant

A
  • Vertical pedigree pattern
  • At least one parent affected
  • Child of affected person has 1/2 chance of being affected
  • Males and females equally affected
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2
Q

Huntington’s disease

A
  • Motor, cognitive and psychiatric dysfunction –> ‘hyperkinesia’
  • Unstable CAG triplet repeats on chromosome 4 –> Huntington protein aggregate –> toxic = cell death
  • repeats increase over generations –> severity increases
  • Treatment to ease symptoms but no cure
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3
Q

Symptoms of Huntington’s

A

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

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4
Q

Osteogenesis Imperfecta

A
  • TYPE 1 = insufficient collagen
  • TYPE 2/3/4 = abnormal protein
  • Interrupts normal protein function –> weakens connective tissue esp. in bones
  • Brittle bones = easily break
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5
Q

Symptoms of OI

A

hearing loss, breathing, short height, blue tinge to whites of eye

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6
Q

Autosomal dominant: mutated gene effects

A

GAIN OF FUNCTION = protein with new function –> increased effect
DOMINANT NEGATIVE EFFECT = binds with and reduces protein activity
INSUFFICIENT = less protein produced –> not enough for normal function

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7
Q

Features of Autosomal Recessive

A
  • Horizontal pedigree
  • No parent affected
  • Skips generations
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8
Q

What increases probability of occurrence of autosomal recessive diseases?

A

consanguinity

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9
Q

CYSTIC FIBROSIS

A
  • mutation in CFTR gene on chromosome 7
  • defective Cl- channels
  • disruption to salt/water regulation –> thick mucus
  • failure to thrive, impaired airway defence –> respiratory infections, digestive issues
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10
Q

Autosomal recessive: mutated gene effects

A

LOSS OF FUNCTION

  • work less well
  • degraded faster
  • present in adequate amounts
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11
Q

X-linked recessive: father affected

A 
Daughters = carriers
Sons = NOT affected
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12
Q

Haemophilia

A
  • Blood clotting disorder –> easy bruising, heavy/more frequent bleeding
  • Factors VIII or IX missing
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13
Q

Fabry’s disease

A
  • female carriers show subtle sign of disease

- build up of fat: acroparasthesia, agiokeratomas, hypohidrosis, tinnitus, GIT issues, corneal opacity

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14
Q

X-linked dominant: Father affected

A
  • all daughters affected
  • no sons affected

condition milder and more variable in females than males

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15
Q

X-linked hypophosphatemia

A
  • kidneys can’t retain phosphate –> vitamin D resistance rickets
  • XLH gene mutation resulting in inactivity of PHEX protein –> enzyme primarily active in bones and teeth
  • rickets, growth problems, serum phosphate, osteomalacia, fractures, psuedofractures
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16
Q

Y-linked: RETINITIS PIGMENTOSA

A
  • mutation in RPY gene –> retinal cells producing defective protein
  • trouble seeing at night, decreased peripheral vision
17
Q

Mitochondrial Inheritance

A
  • maternally affected
  • affected father never affects children
  • vertical pattern
  • unrelated multi-system symptoms esp. motor and nerve function
18
Q

Variable expressivity of mitochondrial inheritance

A
  • multiple mitochondria in each cell
  • only express disease effects above a threshold
  • develops with age –> accumulation of mutant mitochondrias
  • all mitochondria inherited from mother –> random segregation
    SEVERITY VARIES WITH:
    –> amount of WT to mutated mtDNA
    –> severity of mutation
19
Q

LHON

A
  • visual loss in young adulthood

- degeneration of optic nerve and retina from mitochondrial impairment

20
Q

Why use pedigrees?

A
  • clear simple summary of information
  • identify potential carriers of risk gene
  • can spot patterns easily
  • calculate risk of passing on disease
21
Q

MEN-1

A
  • mutated MEN-1 gene (tumour suppressor)
  • affected people have one allele mutated –> 2nd allele mutated over time –> benign tumour
  • adenoma –> hormone producing
  • tumours develop after inactivation of both MEN1 copies at chromosome 11
22
Q

What is risk?

A

Risk is a calculation of the predicated chance of having disease or being carrier

23
Q

What affects risk?

A
  • which side of family disease is on (x-linked, mitochondrial)
  • ethnic background
  • info about the person e.g. phenotype, biological sex, etc
24
Q

Hereditary Haemochromatosis

A
  • AUTOSOMAL RECESSIVE
  • mutation in human homeostatic iron regulator protein (HFE) –> excess iron absorption and build-up –> can’t excrete excess iron –> tired + fatigue
25
Q

In Multiple Endocrine Neoplasia type 1 (MEN1), why do not all people with mutation in MEN1 tumour suppressor gene develop same type of adenoma at same time?

A

A second event has to occur to promote tumour formation, which is based on environmental differences

26
Q

Why do only 10% of people with hereditary haemochromatosis have clinically relevant iron accumulation?

A

Dietary load of iron can vary considerably

Lower levels of intake are associated with improved disease prognosis

27
Q

What gene is responsible for 80% of your eye colour?

A

OCA-2

28
Q

What is the second most important gene for eye colour and what does it do?

A

HERC-2

Controls activity of OCA-2

29
Q

If you have Active HERC-2 and Active OCA-2 what eye colour will you have?

A

Brown eyes [Pic]

30
Q

What causes the difference in disease progression between Duchenne and Becker muscular dystrophy?

A

In DMD there is frame shift deletion in dystrophin gene and so no active dystrophin is produced

In Becker Muscular dystrophy the mutation does not result in frame shift and so active dystrophin is produced whilst in shorter form, retains activity

31
Q

What is a trinucleotide repeat expansion?

A

Mutation in which a region of 3 repeated nucleotides in the genome increases in number during DNA replication

As number of repeats increases, it reaches a threshold at above which they are no longer stable during DNA replication and number of repeats increases each subsequent round of DNA replication

This alters protein function

Greater number of repeats results in more sever phenotype

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