Genetics - First Aid USMLE Flashcards
Modes of inheritance
What mode of Inheritance is presented here?
Modes of inheritance
X-linked recessive
Inheritance Pattern of:
Wiskott-Aldrich syndrome
Inheritance Pattern
Wiskott-Aldrich syndrome - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Loss of heterozygosity
Genetics - First Aid 2019
Example(s) for - Loss of heterozygosity
Retinoblastoma and the “two-hit hypothesis,”
Lynch syndrome (HNPCC), Li-Fraumeni
syndrome.
Genetic disorders by Chromosome
Cri-du-chat syndrome, familial adenomatous polyposis
Genetic disorders by Chromosome
Cri-du-chat syndrome, familial adenomatous polyposis
Chromosome 5
Inheritance Pattern of:
Familial Adenomatous Polyposis
Inheritance Pattern
Familial Adenomatous Polyposis- Autosomal Dominant
Inheritance Pattern of:
Ornithine transcarbamylase deficiency
Inheritance Pattern
Ornithine transcarbamylase deficiency - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Codominance
Genetics - First Aid 2019
Example(s) for - Codominance
Blood groups A, B, AB; α1-antitrypsin
deficiency; HLA groups.
Inheritance Pattern of:
Friedreich ataxia
Inheritance Pattern
Friedreich ataxia - Autosomal Recessive
Inheritance Pattern of:
Achondroplasia
Inheritance Pattern
Achondroplasia - Autosomal Dominant
Inheritance Pattern of:
Bruton agammaglobulinemia
Inheritance Pattern
Bruton agammaglobulinemia - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Genetic disorders by Chromosome
von Hippel-Lindau disease, renal cell carcinoma
Genetic disorders by Chromosome
von Hippel-Lindau disease, renal cell carcinoma
Chromosome 3
Inheritance Pattern of:
Ocular albinism
Inheritance Pattern
Ocular albinism - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Modes of inheritance
Autosomal dominant: Often due to defects in ________ genes. Many generations, both males and females are affected.
Modes of inheritance
Autosomal dominant: Often due to defects in structural genes. Many generations, both males and females are affected.
Modes of inheritance
What mode of Inheritance is presented here?
Modes of inheritance
Autosomal ressecive
Inheritance Pattern of:
Li-Fraumeni syndrome
Inheritance Pattern
Li-Fraumeni syndrome - Autosomal Dominant
Genetics - First Aid 2019
Genetic terms: Definition
Locus heterogeneity
Genetics - First Aid 2019
Definition: Locus heterogeneity
Mutations at different loci can produce a similar
phenotype.
Inheritance Pattern of:
Oculocutaneous albinism
Inheritance Pattern
Oculocutaneous albinism- Autosomal Recessive
Inheritance Pattern of:
von Hippel-Lindau disease
Inheritance Pattern
von Hippel-Lindau disease - Autosomal Dominant
Genetics - First Aid 2019
Genetic terms: Definition
Pleiotropy
Genetics - First Aid 2019
Definition: Pleiotropy
One gene contributes to multiple phenotypic
effects.
Inheritance Pattern of:
Fabry disease
Inheritance Pattern
Fabry disease- X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Inheritance Pattern of:
Multiple Endocrine Neoplasias (MEN)
Inheritance Pattern
Multiple Endocrine Neoplasias (MEN) - Autosomal Dominant
Genetic disorders by Chromosome
ADPKD (PKD1), α-globin gene defects (eg, α-thalassemia), tuberous sclerosis (TSC2)
Genetic disorders by Chromosome
ADPKD (PKD1), α-globin gene defects (eg, α-thalassemia), tuberous sclerosis (TSC2)
Chromosome 16
Inheritance Pattern of:
Mucopolysaccharidoses (except Hunter syndrome)
Inheritance Pattern
Mucopolysaccharidoses - Autosomal Recessive
(except Hunter syndrome)
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Variable expressivity
Genetics - First Aid 2019
Example(s) for - Variable expressivity
2 patients with neurofibromatosis type 1 (NF1) or Polydactyly may have varying disease severity.
Genetic disorders by Chromosome
Neurofibromatosis type 1, BRCA1, TP53
Genetic disorders by Chromosome
Neurofibromatosis type 1, BRCA1, TP53
Chromosome 17
Modes of inheritance
Mitochondrial inheritance: Mitochondrial myopathies
Modes of inheritance
Mitochondrial myopathies - rare disorders;
often present with myopathy, lactic acidosis,
and CNS disease, eg, MELAS syndrome
(mitochondrial encephalomyopathy, lactic
acidosis, and stroke-like episodes). 2° to
failure in oxidative phosphorylation.
Inheritance Pattern of:
Hereditary Spherocytosis
Inheritance Pattern
Hereditary Spherocytosis - Autosomal Dominant
Disorders of imprinting
Prader-Willi syndrome - Chromosome and Disomy Associated:
Disorders of imprinting
Prader-Willi syndrome - Associated with:
Associated with a mutation or deletion of chromosome 15 of paternal origin. Prader has no Papa (Paternal deletion).
25% of cases are due to maternal uniparental disomy.
Inheritance Pattern of:
hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome)
Inheritance Pattern
hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome) - Autosomal Dominant
Inheritance Pattern of:
Hemochromatosis
Inheritance Pattern
Hemochromatosis - Autosomal Recessive
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Heteroplasmy
Genetics - First Aid 2019
Example(s) for - Heteroplasmy
mtDNA passed from mother to all children.
Genetics - First Aid 2019
Genetic terms: Definition
Anticipation
Genetics - First Aid 2019
Definition: Anticipation
Increased severity or earlier onset of disease in
succeeding generations.
Genetics - First Aid 2019
If a population is in _Hardy-Weinberg
equilibrium_ and if p and q are the frequencies
of separate alleles, then: p2 + 2pq + q2 = 1 and
p + q = 1, which implies that:
Genetics - First Aid 2019
Hardy-Weinberg equilibrium: The values of p and q remain constant from generation to generation.
p2 = frequency of homozygosity for allele A
q2 = frequency of homozygosity for allele a
2pq = frequency of heterozygosity (carrier
frequency, if an autosomal recessive disease).
The frequency of an X-linked recessive disease
in males = q and in females = q2.
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Incomplete Penetrance
Genetics - First Aid 2019
Example(s) for - Incomplete Penetrance
BRCA1 gene mutations do not always result in
breast or ovarian cancer.
Inheritance Pattern of:
Cystic Fibrosis
Inheritance Pattern
Cystic Fibrosis - Autosomal Recessive
Inheritance Pattern of:
Marfan syndrome
Inheritance Pattern
Marfan syndrome - Autosomal Dominant
Genetics - First Aid 2019
Genetic terms: Definition
Incomplete Penetrance
Genetics - First Aid 2019
Definition: Incomplete Penetrance
Not all individuals with a mutant genotype
show the mutant phenotype.
% penetrance × probability of inheriting
genotype = risk of expressing phenotype.
Inheritance Pattern of:
PKU
Inheritance Pattern
Phenylketonuria - Autosomal Recessive
Genetics - First Aid 2019
Genetic terms: Definition
Dominant negative mutation
Genetics - First Aid 2019
Definition: Dominant negative mutation
Exerts a dominant effect. A heterozygote
produces a nonfunctional altered protein that
also prevents the normal gene product from
functioning.
Genetics - First Aid 2019
Genetic terms: Definition
Allelic heterogeneity
Genetics - First Aid 2019
Definition: Allelic heterogeneity
Different mutations in the same locus
produce the same phenotype.
Genetic disorders by Chromosome
Hemochromatosis (HFE)
Genetic disorders by Chromosome
Hemochromatosis (HFE)
Chromosome 6
Genetics - First Aid 2019
Genetic terms: Definition
X-inactivation (lyonization)
Genetics - First Aid 2019
Definition: X-inactivation (lyonization)
one copy of female X chromosome forms a
transcriptionally inactive Barr body. Female
carriers variably affected depending on the
pattern of inactivation of the X chromosome
carrying the mutant vs normal gene.
Genetics - First Aid 2019
Genetic terms: Definition
Linkage disequilibrium
Genetics - First Aid 2019
Definition: Linkage disequilibrium
Tendency for certain alleles at 2 linked
loci to occur together more or less often
than expected by chance. Measured in a
population, not in a family, and often varies in
different populations.
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Pleiotropy
Genetics - First Aid 2019
Example(s) for - Pleiotropy
Untreated phenylketonuria (PKU) manifests with light skin, intellectual disability, and musty body odor.
Inheritance Pattern of:
Wilson disease
Inheritance Pattern
Wilson disease - Autosomal Recessive
Modes of inheritance
What mode of Inheritance is presented here?
Modes of inheritance
Autosomal dominant
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Mosaicism
Genetics - First Aid 2019
Example(s) for - Mosaicism
McCune-Albright syndrome—Gs-protein
activating mutation leads to unilateral
café-au-lait spots with ragged edges, polyostotic fibrous dysplasia (bone is replaced by collagen and fibroblasts), and at least one endocrinopathy (eg, precocious puberty). Lethal if mutation occurs before fertilization (affecting all cells), but survivable in patients with mosaicism.
Inheritance Pattern of:
Thalassemias
Inheritance Pattern
Thalassemias - Autosomal Recessive
Genetics - First Aid 2019
Genetic terms: Definition
Uniparental disomy
Genetics - First Aid 2019
Definition: Uniparental disomy
Offspring receives 2 copies of a chromosome from
1 parent and no copies from the other parent. Uniparental is euploid. Most occurrences of uniparental disomy result in normal phenotype.
Modes of inheritance
Autosomal dominant: Often _______ (multiple apparently unrelated effects) and _______ _______ (different between individuals). Family history crucial
to diagnosis. With one affected (heterozygous)
parent, on average, ½ of children affected.
Modes of inheritance
Autosomal dominant: Often pleiotropic (multiple apparently unrelated effects) and variably expressive (different between individuals). Family history crucial
to diagnosis. With one affected (heterozygous)
parent, on average, ½ of children affected.
Disorders of imprinting
AngelMan syndrome - Chromosome and Disomy Associated:
Disorders of imprinting
AngelMan syndrome - Associated with:
Associated with mutation or deletion of
the UBE3A gene on the maternal copy of
chromosome 15.
5% of cases due to paternal uniparental disomy.
Inheritance Pattern of:
ARPKD
Inheritance Pattern
ARPKD - Autosomal Recessive
(Autosomal Recessive Polycystic Kidney Disease)
Modes of inheritance
Mitochondrial inheritance: Transmitted only through the mother. ___ offspring of affected females may show signs of disease. _______ ________ in a population or even within a family due to heteroplasmy.
Modes of inheritance
Mitochondrial inheritance: Transmitted only through the mother. All offspring of affected females may show signs of disease. Variable expression in a population or even
within a family due to heteroplasmy.
Inheritance Pattern of:
Tuberous Sclerosis
Inheritance Pattern
Tuberous Sclerosis - Autosomal Dominant
Inheritance Pattern of:
Hunter syndrome
Inheritance Pattern
Hunter syndrome - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Genetics - First Aid 2019
Genetic terms: Definition
Codominance
Genetics - First Aid 2019
Definition: Codominance
Both alleles contribute to the phenotype of the
heterozygote.
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Anticipation
Genetics - First Aid 2019
Example(s) for - Anticipation
Trinucleotide repeat diseases (eg, Huntington
disease).
Genetics - First Aid 2019
Genetic terms: Definition
Loss of heterozygosity
Genetics - First Aid 2019
Definition: Loss of Heterozygosity
If a patient inherits or develops a mutation in
a tumor suppressor gene, the complementary
allele must be deleted/mutated before cancer
develops. This is not true of oncogenes.
Genetic disorders by Chromosome
ADPKD (PKD2), achondroplasia, Huntington disease
Genetic disorders by Chromosome
ADPKD (PKD2), achondroplasia, Huntington disease
Chromosome 4
Genetics - First Aid 2019
Genetic terms: Definition
Imprinting
Genetics - First Aid 2019
Imprinting
one gene copy is silenced by methylation, and only the other copy is expressed → parent-of-origin effects.
Inheritance Pattern of:
Sickle Cell anemia
Inheritance Pattern
Sickle Cell anemia - Autosomal Recessive
Genetic disorders by Chromosome
Edwards syndrome
Genetic disorders by Chromosome
Edwards syndrome
Chromosome 18
Genetic disorders by Chromosome
Prader-Willi syndrome, Angelman syndrome, Marfan syndrome
Genetic disorders by Chromosome
Prader-Willi syndrome, Angelman syndrome, Marfan syndrome
Chromosome 15
Genetics - First Aid 2019
Genetic terms:
Hardy-Weinberg law assumptions (4)
Genetics - First Aid 2019
Hardy-Weinberg law assumptions include:
- No mutation occurring at the locus
- Natural selection is not occurring
- Completely random mating
- No net migration
Genetics - First Aid 2019
Genetic terms: Definition
Somatic Mosaicism
Genetics - First Aid 2019
Definition: Somatic Mosaicism
Presence of genetically distinct cell lines in the
same individual. In Somatic mosaicism, the mutation arises from mitotic errors after fertilization and propagates through multiple tissues or organs.
Genetic disorders by Chromosome
Down syndrome
Genetic disorders by Chromosome
Down syndrome
Chromosome 21
Modes of inheritance
X-linked Dominant: Example(s)
Modes of inheritance
Hypophosphatemic rickets—formerly known as
vitamin D–resistant rickets. Inherited disorder
resulting in higher phosphate wasting at proximal
tubule. Results in rickets-like presentation.
Other examples: fragile X syndrome, Alport
syndrome.
Genetic disorders by Chromosome
Wilms tumor, β-globin gene defects (eg, sickle cell disease, β-thalassemia), MEN1
Genetic disorders by Chromosome
Wilms tumor, β-globin gene defects (eg, sickle cell disease, β-thalassemia), MEN1
Chromosome 11
Inheritance Pattern of:
Duchenne (and Becker) muscular dystrophy
Inheritance Pattern
Duchenne (and Becker) muscular dystrophy - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Inheritance Pattern of:
Hemophilia A and B
Inheritance Pattern
Hemophilia A and B - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Modes of inheritance
- *X-linked recessive:** Sons of heterozygous mothers have a ___ chance of being affected. No ____-to-____
transmission. Skips generations.
Modes of inheritance
- *X-linked recessive:** Sons of heterozygous mothers have a 50% chance of being affected. No male-to-male
transmission. Skips generations.
Inheritance Pattern of:
Huntington disease
Inheritance Pattern
Huntington disease - Autosomal Dominant
Modes of inheritance
X-linked recessive: Commonly more severe in males. Females usually must be _________ to be affected.
Modes of inheritance
X-linked recessive: Commonly more severe in males. Females usually must be homozygous to be affected.
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Uniparental disomy
Genetics - First Aid 2019
Example(s) for - Uniparental disomy
Consider UPD in an individual manifesting a recessive
disorder when only one parent is a carrier.
Examples: Prader-Willi and Angelman
syndromes.
Disorders of imprinting
AngelMan syndrome - Signs and Symptoms
Disorders of imprinting
AngelMan syndrome: Results in inappropriate laughter (“happy puppet”), seizures, ataxia, and severe intellectual
disability.
Disorders of imprinting
Prader-Willi syndrome:Signs and Symptoms
Disorders of imprinting
Prader-Willi syndrome: Results
in hyperphagia, obesity, intellectual disability,
hypogonadism, and hypotonia.
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Dominant negative mutation
Genetics - First Aid 2019
Example(s) for - Dominant negative mutation
Mutation of a transcription factor in its allosteric
site. Nonfunctioning mutant can still bind
DNA, preventing wild-type transcription factor
from binding.
Genetic disorders by Chromosome
Neurofibromatosis type 2, DiGeorge syndrome
Genetic disorders by Chromosome
Neurofibromatosis type 2, DiGeorge syndrome (22q11)
Chromosome 22
Inheritance Pattern of:
Neurofibromatosis type 1 (von
Recklinghausen disease) and type 2
Inheritance Pattern
Neurofibromatosis type 1 (von
Recklinghausen disease) and type 2 - Autosomal Dominant
Modes of inheritance
Autosomal recessive: Higher risk in __________ families. Unaffected individual with affected sibling has
2/3 probability of being a carrier.
Modes of inheritance
Autosomal recessive: Higher risk in consanguineous families. Unaffected individual with affected sibling has
2/3 probability of being a carrier.
Disorders of imprinting
AngelMan syndrome: Silent Gene
Disorders of imprinting
AngelMan syndrome: Silent Gene Paternally derived gene is silenced (imprinted). Disease occurs when the Maternal allele is deleted or mutated.
Genetics - First Aid 2019
Genetic terms: Definition
Uniparental disomy - Heterodisomy Vs. IsodIsomy
Genetics - First Aid 2019
Definition: Heterodisomy Vs. Isodisomy
HeterodIsomy (heterozygous) indicates a meiosis I error. IsodIsomy (homozygous) indicates a meiosis II error or postzygotic chromosomal duplication of one of a pair of chromosomes, and loss of the other of the original pair.
Modes of inheritance
Autosomal recessive: With 2 carrier (heterozygous) parents, on average: _ of children will be affected (homozygous), _ of children will be carriers, and _ of
children will be neither affected nor carriers.
Modes of inheritance
Autosomal recessive: With 2 carrier (heterozygous) parents, on average: ¼ of children will be affected (homozygous), ½ of children will be carriers, and ¼ of
children will be neither affected nor carriers.
Modes of inheritance
What mode of Inheritance is presented here?
*Hint: Fathers transmit to all daughters
Modes of inheritance
X-linked dominant
Modes of inheritance
What mode of Inheritance is presented here?
*Hint: All offspring of affected females may show signs of
disease.
Modes of inheritance
Mitochondrial Inheritance
Inheritance Pattern of:
Lesch-Nyhan syndrome
Inheritance Pattern
Lesch-Nyhan syndrome - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Modes of inheritance
X-linked Dominant: Transmitted through both parents. Mothers transmit to 50% of daughters and sons; fathers
transmit to ___ daughters but no sons.
Modes of inheritance
X-linked Dominant: Transmitted through both parents. Mothers transmit to 50% of daughters and sons; fathers
transmit to all daughters but no sons.
Genetics - First Aid 2019
Genetic terms: Definition
Heteroplasmy
Genetics - First Aid 2019
Definition: Heteroplasmy
Presence of both normal and mutated
mtDNA, resulting in variable expression in
mitochondrially inherited disease.
Genetics - First Aid 2019
Genetic terms: Definition
Gonadal Mosaicism
Genetics - First Aid 2019
Definition: Gonadal Mosaicism
Presence of genetically distinct cell lines in the
same individual. In Gonadal mosaicism, the mutation is only in egg or sperm cells. If parents and relatives do not
have the disease, suspect gonadal (or germline) mosaicism.
Genetic disorders by Chromosome
Fragile X syndrome, X-linked agammaglobulinemia, Klinefelter syndrome (XXY)
Genetic disorders by Chromosome
Chromosome X
Inheritance Pattern of:
Glycogen storage diseases
Inheritance Pattern
Glycogen storage diseases - Autosomal Recessive
Modes of inheritance
Mitochondrial inheritance: Leber hereditary optic neuropathy
Modes of inheritance
Leber hereditary optic neuropathy - cell
death in optic nerve neurons → subacute
bilateral vision loss in teens/young adults, 90%
males. Usually permanent.
Inheritance Pattern of:
Familial Hypercholesterolemia
Inheritance Pattern
Familial Hypercholesterolemia - Autosomal Dominant
Inheritance Pattern of:
G6PD deficiency
Inheritance Pattern
G6PD deficiency - X-linked Recessive
Mneumonic: Obliviously Female Will Often Give Her Boys Her x-Linked Disorders
Genetics - First Aid 2019
Genetic terms: Definition
Variable expressivity
Genetics - First Aid 2019
Definition: Variable expressivity
Patients with the same genotype have varying
phenotypes.
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Locus heterogeneity
Genetics - First Aid 2019
Example(s) for - Locus heterogeneity
Albinism.
Genetic disorders by Chromosome
Friedreich ataxia, tuberous sclerosis (TSC1)
Genetic disorders by Chromosome
Friedreich ataxia, tuberous sclerosis (TSC1)
Chromosome 9
Disorders of imprinting
Prader-Willi syndrome:Silent Gene
Disorders of imprinting
Prader-Willi syndrome:Silent Gene Maternally derived genes are silenced (imprinted). Disease occurs when the Paternal allele is deleted or mutated.
Inheritance Pattern of:
Kartagener syndrome
Inheritance Pattern
Kartagener syndrome - Autosomal Recessive
Genetic disorders by Chromosome
Patau syndrome, Wilson disease, retinoblastoma (RB1), BRCA2
Genetic disorders by Chromosome
Patau syndrome, Wilson disease, retinoblastoma (RB1), BRCA2
Chromosome 13
Genetic disorders by Chromosome
Williams syndrome, Cystic fibrosis
Genetic disorders by Chromosome
Williams syndrome, Cystic fibrosis
Chromosome 7
Inheritance Pattern of:
Myotonic Muscular Dystrophy
Inheritance Pattern
Myotonic Muscular Dystrophy - Autosomal Dominant
Genetics - First Aid 2019
Genetic terms: Example(s) for -
Allelic heterogeneity
Genetics - First Aid 2019
Example(s) for - Allelic heterogeneity
β-thalassemia.
Modes of inheritance
Autosomal recessive: Often due to ______ deficiencies. Usually seen in only 1 generation. Commonly more severe than dominant disorders; patients often present
in childhood.
Modes of inheritance
Autosomal recessive: Often due to enzyme deficiencies. Usually seen in only 1 generation. Commonly more severe than dominant disorders; patients often present
in childhood.
Inheritance Pattern of:
Sphingolipidoses
Inheritance Pattern
Sphingolipidoses - Autosomal Recessive
(except Fabry disease)
Inheritance Pattern of:
ADPKD
Inheritance Pattern
ADPKD - Autosomal Dominant
(Autosomal Dominant Polycystic Kidney Disease)