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USMLE Step 1 > Genetics > Flashcards

Genetics Flashcards

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USMLE® Step 1 flashcards
1
Q

Congenital Disesae

A

A disease that is present from birth

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2
Q

Hemizygotic

A

Has 1 allele instead of the usual 2 (e.g. sex chromosomes in males)

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3
Q

Polymorphism

A

The existence of multiple alleles for a particular gene

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4
Q

How many combinations of chromosomes will meiosis generate for X chromosomes?

A

2^X

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5
Q

What is a metacentric chromosome?

A

The centromere is located in the center of the chromosome

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6
Q

What is a submetacentric chromosome?

A

The centromere is closer to one of the ends.

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7
Q

What is an acrocentric chromosome?

A

The centromere is close to the telomere.

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8
Q

Aneuploidy

A

The loss of gain of one or more chromosomes; at least one set of chromosomes is incomplete; caused by nondisjunction

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9
Q

Polyploidy

A

More than two complete sets of chromosomes

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10
Q

Euploid

A

Containing the exact multiple of the number of chromosomes in a normal gamete (1=haploid, 2=diploid)

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11
Q

Partial Monosomy

A

Only a portion of the chromosome has one copy

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12
Q

Mosaicism

A

The presence of at least two cell lines with different genotype in an individual

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13
Q

Balanced chromosome arrangement

A

No loss or gain of essential chromosomal material

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14
Q

Unbalanced chromosome arrangement

A

Loss or gain of essential chromosomal material

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15
Q

Types of chromosomal structural abnormalities

A

Translocations (e.g. Robertsonian - fusion at the centromere of two acrocentric chromosomes like 14 and 21)

Inversions (pericentric vs. paracentric)

Isochromosome (caused by double-stranded break near centromere)

Insertions

Deletions

Duplications

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16
Q

Compound heterozygote

A

Two different alleles may cause disease

17
Q

Autosomal Recessive Diseases

A

Gene often encodes an enzyme: Sickle cell anemia Cystic fibrosis Tay-Sachs disease Phenylketonuria Bloom’s syndrome α- and β-Thalassemia

18
Q

What kinds of molecular disorders are typically dominant?

A

Gene products encode receptors, something in a pathway, etc. Haploinsufficiency (e.g. receptors) Dominant negative (mutant protein interferes with normal protein) New or enhanced property of the protein (e.g. overproduction of a receptor, toxic protein)

19
Q

Name some X-linked recessive diseases?

A

Duchenne muscular dystrophy Hemophilia (A and B) Red-green color blindness Nephrogenic diabetes insipidus

20
Q

Name some autosomal dominant diseases?

A

Familial hypercholesterolemia Osteogenesis imperfecta type II Achondroplasia (short-limed dwarfism) Huntington disease Glucose-6-phosphate dehydrogenase deficiency

21
Q

Name some X-linked dominant diseases?

A

Fragile X syndrome (both sexes) Vitamin D resistant rickets (both sexes) Aicardi syndrome (lethal in males) Incontinentia pigmenti (lethal in males) Rett syndrome (lethal in males)

22
Q

Alellic Heterogeneity

A

Different mutations in the same gene

23
Q

Locus (Genetic) Heterogeneity

A

The same condition can be caused by mutations in different genes

24
Q

Incomplete Penetrance

A

The likelihood that the disease allele will result in the disease (all or nothing)

25
Q

Pleiotropy

A

Diverse effects of a single gene on several organs; often shows variable expression

26
Q

Expressivity/Variable Expression

A

The degree of clinical manifestation of the same mutant allele in different individuals

27
Q

Anticipation

A

Increasing severity of disease in successive generations (earlier onset, worsening of symptoms); often due to unstable repeat expansion.

Examples include Huntington Disease, Fragile X Syndrome, Myotonic Dystrophy, and Friedreich ataxia

28
Q

Heteroplasmy

A

The presence of more than one type of mitochondrial DNA

29
Q

Uniparental disomy

A

Both copies of a chromosome are received from the same parent; can cause problems with imprinting

30
Q

Polygenic

A

Caused by the combined actions of two or more genes; proportional to the degree of relatedness

31
Q

Multifactorial

A

Caused by the combined actions of two or more genes and environmental factors; proportional to the degree of relatedness

32
Q

Concordance

A

The presence of a given trait in both members of a pair of twins; should be 100% if disease is purely genetic; higher concordance in MZ vs DZ twins is evidence of strong genetic component

33
Q

Name some mitochondrial diseases?

A

Mitochondrial disorders are inherited exclusively from mothers

  1. Leber hereditary optic neuropathy: bilateral blindness
  2. Myoclonic epilepsy with ragged red fibers: myoclonic seizures, myopathy associated with exercise, irregularly shaped (ragged red) muscle fibers
  3. Mitochondrial encephalomyopathy with lactic acidosis:

USMLE Step 1 (20 decks)

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