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UKMLA Prep > Genetics > Flashcards

Genetics Flashcards

1
Q

What is the inheritance pattern of autosomal dominant diseases?

A

Both homozygotes and heterozygotes manifest disease

There is no carrier state in autosomal dominant diseases.

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2
Q

In autosomal dominant inheritance, what percentage of children will inherit the disease from an affected parent?

A

50%

This applies to each child regardless of the parent’s sex.

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3
Q

Are both males and females affected in autosomal dominant diseases?

A

Yes

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4
Q

What is non-penetrance in the context of genetic diseases?

A

Lack of clinical signs and symptoms despite the presence of an abnormal gene

Example: 40% of individuals with otosclerosis may show no symptoms.

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5
Q

What is a spontaneous mutation in genetics?

A

A new mutation occurring in one of the gametes

Example: 80% of individuals with achondroplasia have unaffected parents.

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6
Q

List three examples of autosomal dominant conditions.

A
  • Achondroplasia
  • Huntington’s disease
  • Marfan’s syndrome
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7
Q

What is the inheritance pattern of autosomal recessive diseases?

A

Only homozygotes are affected

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8
Q

In autosomal recessive inheritance, what is the chance of two heterozygote parents having an affected child?

A

25%

They also have a 50% chance of having a carrier child and a 25% chance of having an unaffected child.

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9
Q

Are autosomal recessive disorders typically metabolic or structural?

A

Metabolic

Notable exceptions exist, such as certain structural conditions.

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10
Q

List three examples of autosomal recessive conditions.

A
  • Cystic fibrosis
  • Sickle cell anaemia
  • Wilson’s disease
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11
Q

What are the two types of cell division?

A

Mitosis and meiosis

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12
Q

What is the main outcome of mitosis?

A

2 diploid daughter cells

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13
Q

What is the main outcome of meiosis?

A

4 haploid daughter cells

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14
Q

What occurs during the prophase of mitosis?

A

Chromatin in the nucleus condenses

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15
Q

List three key features of Patau syndrome.

A
  • Microcephalic
  • Cleft lip/palate
  • Polydactyly
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16
Q

Which congenital infection is most common in the UK?

A

Cytomegalovirus

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17
Q

What are the characteristic features of congenital rubella syndrome?

A
  • Sensorineural deafness
  • Congenital cataracts
  • Congenital heart disease
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18
Q

What is the risk of inherited defects in consanguineous couples?

A

Approximately double that of a non-related couple

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19
Q

What is the inheritance pattern of Fabry disease?

A

X-linked recessive

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20
Q

What causes homocystinuria?

A

Deficiency of cystathionine beta synthase

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21
Q

What is the hallmark of mitochondrial diseases?

A

Inheritance only via the maternal line

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22
Q

What is the role of the p53 gene?

A

Tumor suppressor gene that prevents entry into the S phase until DNA is repaired

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23
Q

What is penetrance in genetics?

A

The proportion of individuals with a disease-causing allele who express the related phenotype

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24
Q

What is expressivity in genetics?

A

The extent to which a genotype shows its phenotypic expression in an individual

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25
Q

What is phenylketonuria (PKU)?

A

An autosomal recessive condition caused by a defect in phenylalanine metabolism

26
Q

What is a key feature of McCune-Albright syndrome?

A

Precocious puberty

27
Q

What are ‘red, ragged fibres’ indicative of in histology?

A

Mitochondrial disease

28
Q

How do oncogenes differ from tumor suppressor genes?

A

Oncogenes promote cancer through gain of function; tumor suppressor genes increase cancer risk through loss of function

29
Q

What is the main enzyme defect in phenylketonuria (PKU)?

A

Phenylalanine hydroxylase

This enzyme converts phenylalanine to tyrosine.

30
Q

What are the high levels of phenylalanine associated with?

A

Learning difficulties and seizures

High phenylalanine can lead to developmental problems.

31
Q

Where is the gene for phenylalanine hydroxylase located?

A

Chromosome 12

32
Q

What is the incidence of PKU?

A

1 in 10,000 live births

33
Q

What is a classic feature of a child with PKU?

A

Fair hair and blue eyes

34
Q

What is the Guthrie test used for?

A

Diagnosis of PKU and other biochemical disorders

It is a ‘heel-prick’ test done at 5-9 days of life.

35
Q

What does polymerase chain reaction (PCR) require?

A

Sample DNA, two DNA primers, and a thermostable DNA polymerase (Taq)

36
Q

What is the main advantage of PCR?

A

Sensitivity; only one strand of sample DNA is needed

37
Q

What does reverse transcriptase PCR amplify?

38
Q

What genetic disorder is associated with the absence of the active Prader-Willi gene?

A

Prader-Willi syndrome

39
Q

What are the features of Prader-Willi syndrome?

A

Hypotonia during infancy
Dysmorphic features
Short stature
Hypogonadism and infertility
Learning difficulties
Childhood obesity
Behavioural problems in adolescence

40
Q

What are purines?

A

Adenine and Guanine

Remembered with the mnemonic ‘Pure As Gold’ (Pur A G).

41
Q

What are pyrimidines?

A

Cytosine, Uracil, Thymine

Remembered with the mnemonic ‘Cut Py’ (C U T Py).

42
Q

How many hydrogen bonds occur between Guanine and Cytosine?

A

3 hydrogen bonds

43
Q

How many hydrogen bonds occur between Adenine and Thymine?

A

2 hydrogen bonds

44
Q

What is the clinical significance of purines and pyrimidines?

A

Inhibition of their synthesis can inhibit cellular replication and cause cell death

45
Q

What is the salvage pathway in purine synthesis?

A

Production of purine nucleotides AMP or GMP using free guanine or adenine bases

46
Q

What is the role of HGPRT in purine metabolism?

A

Recycle guanine and hypoxanthine to GMP and IMP, respectively

47
Q

What condition is caused by a deficiency in HGPRT?

A

Lesch-Nyhan syndrome

48
Q

What is the final product of purine degradation?

49
Q

What enzyme converts xanthine to uric acid?

A

Xanthine oxidase

50
Q

What is the consequence of adenosine deaminase (ADA) deficiency?

A

Severe combined immunodeficiency (SCID)

51
Q

What are trinucleotide repeat disorders?

A

Genetic conditions caused by an abnormal number of repeats of a sequence of three nucleotides

52
Q

What phenomenon describes earlier age of onset in successive generations of trinucleotide repeat disorders?

A

Anticipation

53
Q

What is an example of a tumor suppressor gene?

54
Q

What is the inheritance pattern of Turner’s syndrome?

A

Chromosomal disorder affecting females

55
Q

What is a common feature of Turner’s syndrome?

A

Short stature

56
Q

What are the long-term health risks associated with Turner’s syndrome?

A

Aortic dilatation
Dissection

57
Q

What is William’s syndrome caused by?

A

Microdeletion on chromosome 7

58
Q

What are the features of William’s syndrome?

A

Elfin-like facies
Friendly and social demeanor
Learning difficulties
Short stature

59
Q

What type of inheritance do X-linked dominant conditions follow?

A

X-linked dominant fashion

60
Q

What is a key characteristic of X-linked recessive inheritance?

A

Only males are affected

61
Q

What is an exception to male-only X-linked recessive conditions?

A

Turner’s syndrome

62
Q

What are some examples of X-linked recessive conditions?

A

Duchenne muscular dystrophy
Haemophilia A
Fabry’s disease
G6PD deficiency

UKMLA Prep (48 decks)

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