Genetic principles Flashcards

1
Q

What is the difference between somatic cells and gametes?

A
  • Somatic cells are diploid (most body cells)
  • Gametes are haploid
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2
Q

What are alleles?

A

Alternative forms of gene

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3
Q

If a gene displays genetic polymorphism what does this mean?

A

Genes exist in multiple forms (alleles)

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4
Q

What is the locus (plural loci)?

A

Location of allele on chromosome

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5
Q

What is the wild type gene/allele?

A

Gene/allele that is common in most individuals (A in Aa)

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6
Q

What is the difference between a germilne and a somatic mutation?

A

Germ line
- DNA of sperm/eggs
- Transmitted to offspring
- Found in every cell of the body

Somatic mutations
- Acquired during lifespan of cell
- Not transmitted to offspring

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7
Q

What is codominance?

A

When both alleles contribute to phenotype

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8
Q

Give a common example of codominance?

A

Blood groups ABO
AB individuals will express both A and B antigens

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9
Q

What is penetrance?

A

Proportion with allele that express phenotype

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10
Q

What is incomplete penetrance?

A

Not all those with disease mutation develop disease

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11
Q

Give an example of a gene mutation which displays incomplete penetrance?

A

BRCA1 and 2
- Usually Aut dominant disease

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12
Q

What is expressivity?

A

Variations in the phenotype of gene

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13
Q

What is an example of a disease which displays expressivity?

A

Neurofibromatosis type 1 (NF1)
- Aut dom
- 100% penetrance
- Extremely variable severity

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14
Q

What is pleiotropy?

A

One gene which can have multiple different phenotypic effects and traits
- e.g one gene affecting skin, eyes and brain

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15
Q

Give some examples of pleitropy

A
  • PKU - skin, body odor, brain
  • Marfan - CV, limbs
  • CF - pancreas, lungs
  • Osteogenesis imperfecta - eyes, limbs, hearing
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16
Q

What genes are involved in the 2-hit hypothesis?

A

Tumour suppressor genes

17
Q

What is the more colloquial term for loss of heterozygosity?

A

2 hits
- Cancer requiring mutation of both alleles

18
Q

What percentage of retinoblastoma cases are heriditary?

A

40%
- Have one gene mutated in all cells at birth (germline mutation)

19
Q

HNPCC (Lynch syndrome) has a germline mutation in what genes?

A

Mismatch repair genes
- Example of 2-hit hypothesis
- 1 inherited germline mutation
- 2nd ‘hit’/mutation/inactivation will occur during lifetime -> cancer

20
Q

What percentage of those with FAP develop colon cancer?

A

100%
- Prophylactic colectomy

21
Q

What cancers are those with Li-Fraumeni Syndrome most at risk of?

A
  • Sarcoma
  • Breast
  • Leukemia
  • Adrenal gland
22
Q

What gene is mutated in Li-Fraumeni syndrome?

A

TP53

23
Q

What is mosaicism?

A

Gene differences in cells of the same individual

24
Q

What can germline mosaicism appear like?

A

May appear like a sporadic disease in offspring as it is difficult to detect
- In reality it is germline mosaicism passed down from parent

25
Q

What is somatic mosaicism?

A

Gene differences in tissues/organs of an individual that do not involve the germline cells

26
Q

What diseases may have somatic mosaicism?

A
  • Milder forms of Turner syndrome (45X/46XX)
  • Rare forms of Down syndrome (some cells have trisomy 21, others do not)
27
Q

What syndrome is often used as an example of mosaicism?

A

McCune-Albright syndrome

28
Q

What are the features of McCune-Albright syndrome?

A
  • Effects endocrine organs
  • Precocious puberty
  • Fibrous growth in bones (fractures, deformity)
  • Skin pigmentation (Cafe au lait spots. irregular borders)
29
Q

How early can menstraution occur due to precocious puberty in cafe au lait syndrome?

A

2 years old

30
Q

When does the mutation occur in Mccune-Albright syndrome?

A
  • Sporadic mutation in development, after fertilization
  • Only some tissues affected, varied presentation due to
  • Not inherited from parent
31
Q

What gene is somatically mutated in McCune Albright syndrome?

A

GNAS gene

32
Q

What does GNAS gene code for (McCune-Albright)?

A
  • Alpha subunit of G3 protein
  • Activates for adenylyl cyclase
  • Continued stimulation of cAMP signaling
33
Q

Why are germline GNAS mutations never seen?

A

They are lethal as entire body is affected

34
Q

Explain genetic heterogeneity?

A

Same phenotype from different genes/mutations
- Multiple gene mutations often causing the same disease, many diseases have multiple genotypes causing them

35
Q

What is allelic heterogeneity?

A

When multiple different alleles can cause the same disease
- However mutation will be found at the same loci

36
Q

Give 2 examples of diseases which express allelic heterogeneity?

A
  • Beta thalassemia
  • Cystic fibrosis
37
Q

What is locus heterogenity?

A

When mutations at different loci can cause the same disease

38
Q

Give an example of a disease which displays locus hetergeneity?

A

Retinitis Pigmentosum
- X-linked, aut dom and AR forms
- 43 different loci can cause disease

39
Q

How is retinitis pigmentosum inherited?

A

Aut dom