Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Case 7 > Unusual Patterns of Inheritance > Flashcards

Unusual Patterns of Inheritance Flashcards

1
Q

What is the inheritance pattern of complex traits?

A

Polygenic - influenced by many genes which often interact with environmental factors = multifactorial inheritance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the confounding factors in monogenic inheritance?

A
  1. Variable expression - same mutation expressed as different disease phenotypes
  2. Reduced penetrance - not everyone with genetic factors shows symptoms
  3. Sex limitation - mutation predisposes to disease/phenotype in one sex rather than other
  4. Phenocopy - occurrence of disease in family unrelated to familial mutation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the 2 major dominant susceptibility genes for hereditary breast cancer?

A
  • BRCA1

- BRCA2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Give an example of X-linked dominant inheritance

A

X-linked hypophosphatemic rickets

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Give an example of X-linked dominant lethal disease

A
  • Incontinentia pigmenti (NEMO gene)

- Affects women - so severe for men they are non-viable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is seen in affected females with incontinentia pigmenti?

A
  • Blistering (birth - 4m)
  • Wart-like rash (several months)
  • Swirling macular hyper-pigmentation (6m - adult)
  • Linear hypo pigmentation
  • Alopecia, hypodontia, dystrophic nails, retinal detachment, occasional developmental delay
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why does incontinentia pigmenti affect females?

A
  • In females, 1 X-chromosome silenced in each cell
  • Inactivation takes place randomly around blastocyst stage
  • Daughter cells from embryonic cell inherit same inactivated X-chromosome
    Either:
    1. Normal X-chromosome inactivates = cells with NEMO
    2. Mutated X-chromosome inactivated = normal X passed on
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the recurrence risk of incontinentia pigmenti?

A

1/3 unaffected male
1/3 affected female
1/3 unaffected female

Affected males die in utero

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is chimerism?

A

An organism composed of 2 or more populations of genetically distinct cells that originate from different zygotes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is a constitutional mutation?

A

Inherited from a gamete (gremlin mutation) or occurs soon after fertilisation = present in every cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is somatic mosaicism?

A

Some cells lack mutation = milder phenotype.

However, their children = at risk of inheriting change as constitutional mutation = more severe phenotype.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is confined placental mosaicism?

A

Common + can complicate prenatal testing but is absent from baby

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the cause and presentation of Prader Willi Syndrome?

A

Cause = deletion inherited on PATERNAL chromosome 15

  • Neonatal hypotonia + early poor feeding
  • Later = hyperrhagia + obesity
  • Short stature, hypogonadism
  • Mild/mod ID, behaviour problems
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the cause and presentation of Angleman Syndrome?

A

Cause = deletion inherited on MATERNAL chromosome 15

  • Microcephaly, gait ataxia, seizures
  • Severe ID, absent speech, happy demeanour
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is genomic imprinting?

A
  • When genes expression is dependant on which parent it was inherited from
  • Involves epigenetic signals
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Define epigenetics

A
  • Modification on chromosomes without alteration of DNA sequence
  • Alter transcriptional potential of genes through DNA methylation or histone modification
17
Q

Give an example of imprinted inheritance

A

Mother with PWS could have child with AS:

If they inherit deletion paternally but they are mother so reprogram + maternally imprint + pass on

18
Q

What is Uniparental disomy (UPD)?

A
  • When BOTH chromosomes originate from 1 parent
  • Due to non-disjunction at meiosis 1
  • Can have UPD of chromosome + be healthy as long as NO imprinted genes on chromosome
19
Q

What is trisomic rescue?

A

Loss of chromosome from zygote/early embryo -> preserves viability

20
Q

What are potential health problems associated with UPD?

A
  1. Mosaic aneuploidy (if trisomy/monosomy rescue)
  2. Disease due to imprinting
  3. Recessive disease (if isodisomy)
21
Q

What is the presentation of Beckwith-Wiedemann syndrome?

A
  • Large gestational age
  • Exomphalos/umbilical hernia
  • Macroglossia
  • Limb/body overgrowth
  • Neonatal hyper-insulinism
  • Ear creases
  • Nevus flames
  • Risk of cancer
22
Q

What is the presentation of Silver-Russel syndrome?

A
  • Small for gestational age
  • Feeding problems
  • Hypoglycaemia
  • Lack of subcutaneous fat
  • Clinodactyly
  • Proportionate short stature
  • Asymmetry
  • Hypospadias
  • Normal intelligence
23
Q

What is mitochondrial inheritance?

A
  • Transmission from mother to child
  • Sperm do not transmit paternal mitochondria
  • Only maternal mitochondria present in cytoplasm of zygote
24
Q

Which tissues are particularly vulnerable in mitochondrial disorders?

A
  • Energy-hungry tissues

- Often multi-system

25
Q

What is Leber Hereditary Optic Neuropathy (LHON)?

A
  • Sudden, painless, permanent central vision loss, bilateral
  • Optic atrophy
  • Onset in adolescence or as young adult, but can be earlier/later
  • 3 mtDNA mutations cause 95% of LHON
  • Male predominance, but with reduced penetrance in both sexes
26
Q

Do all mitochondrial disorders have mitochondrial inheritance?

A
  • No, only some mitochondrial disorders have mitochondrial inheritance
  • Many proteins in mitochondria come from genes encoded in nuclear genome
  • Disorders of mitochondrial function can be inherited in autosomal or X-linked manner
27
Q

What is Heteroplasmy?

A

Where proportion of mutated mitochondria in cell varies between tissues -> affecting which organs have symptoms = variable expression

28
Q

What is Y-linked inheritance?

A
  • Few traits as not many genes
  • Often involved in fertility - mutations impair reproduction
  • Male-male transmission only
29
Q

What is Pseudo-dominant inheritance?

A

When recessive conditions appear to transmmit dominantly

30
Q

What is Co-dominant inheritance?

A

e. g. ABO blood group
- A + B alleles both co-dominant
- O allele recessive to both

31
Q

What is anticipation?

A
  • Symptoms of genetic disorder become more severe and/or have earlier onset in successive generations
  • Characteristic of trinucleotide repeat disorders
  • Can be coding or non-coding
32
Q

What is the difference between Heterodisomy and Isodisomy?

A
  • Heterodisomy = no-disjunction at meiosis stage 1

- Isodisomy = non-disjunction at meiosis stage 2

Case 7 (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions