Curriculum

17 Sections
1548 Lessons
100 Days

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U01.01 Biochemistry
This biochemistry review for USMLE Step 1 covers essential topics including metabolism, enzymology, and molecular biology.
126
U01.02 Immunology
Prepare for USMLE Step 1 Immunology with a comprehensive review covering foundational concepts, immune system mechanisms, and key disorders to solidify your understanding and boost exam readiness.
42
U01.03 Microbiology
Review essential microbiology topics for the USMLE Step 1, covering key pathogens, mechanisms of disease, and antimicrobial principles critical for mastering infectious disease concepts.
172
U01.04 General Pathology
Explore key concepts in general pathology essential for the USMLE Step 1. This review covers fundamental principles, disease mechanisms, and clinical correlations to help you excel in your medical exam.
35
U01.05 Pharmacology
Master key pharmacology concepts for the USMLE Step 1 with a focus on drug mechanisms, therapeutic uses, adverse effects, and interactions essential for high-yield exam performance.
43
U01.06 Public Health Sciences
Review essential Public Health Sciences topics for the USMLE Step 1, covering epidemiology, biostatistics, health policy, and ethics to strengthen your understanding of foundational public health principles.
53
U01.07 Cardiovascular system
Comprehensive review of essential cardiovascular system topics to help you excel in the USMLE Step 1 exam, covering key concepts from anatomy to pathology.
73
U01.08 Endocrine system
Master essential concepts of the endocrine system for USMLE Step 1, covering hormone regulation, feedback mechanisms, and key disorders to boost your exam readiness.
51
U01.09 Gastrointestinal system
Review key topics in the gastrointestinal system for the USMLE Step 1, covering essential concepts in anatomy, physiology, pathology, and pharmacology to reinforce your understanding and test readiness.
131
U01.10 Hematology and Oncology
This review covers essential Hematology and Oncology topics for the USMLE Step 1, including hematopoiesis, coagulation, anemias, leukemias, lymphomas, and neoplastic syndromes.
148
U01.11 Musculoskeletal, Skin, and Connective Tissue
Review essential topics for the USMLE Step 1 Musculoskeletal, Skin, and Connective Tissue systems, covering anatomy, physiology, pathology, and pharmacology fundamentals critical for exam success.
178
U01.12 Neurology and Special Senses
Master the foundational concepts of Neurology and Special Senses with our USMLE Step 1 review, covering essential topics like neuroanatomy, neurophysiology, and sensory pathways.
143
U01.13 Psychiatry
Psychiatry for the USMLE Step 1 focuses on understanding the pathophysiology, diagnosis, and treatment of psychiatric disorders, with an emphasis on key concepts like neurotransmitter imbalances, mental health disorders, and pharmacology.
83
U01.14 Renal System
The Renal System review for USMLE Step 1 covers key concepts including renal physiology, nephron function, acid-base balance, electrolyte regulation, and renal pathology, crucial for understanding both normal and abnormal kidney functions.
81
U01.15 Reproductive System
The USMLE Step 1 Reproductive System review covers key concepts in human reproduction, including anatomy, physiology, endocrinology, and common pathologies affecting both male and female reproductive health.
124
U01.16 Respiratory System
The Respiratory System review for the USMLE Step 1 covers key concepts in anatomy, physiology, pathophysiology, and pharmacology essential for understanding respiratory diseases and treatments.
61
U01.17 Rapid Review
he USMLE Step 1 Rapid Review covers essential topics across multiple disciplines, providing a concise, high-yield overview to reinforce key concepts and optimize your exam preparation.
5

U01.01.048 Modes of inheritance

Modes of inheritance describe the patterns through which genetic traits or diseases are passed from one generation to the next. Understanding these modes is crucial for diagnosing genetic disorders and predicting recurrence risks.

1. Autosomal Dominant Inheritance

Characteristics

Affects males and females equally.
Seen in every generation; affected individuals usually have at least one affected parent.
Often due to structural gene defects.
Exhibits pleiotropy (multiple unrelated effects) and variable expressivity (different severity among individuals).

Punnett Square Representation

Parent Genotype	A	a
A	AA	Aa
a	Aa	aa

AA: Affected
Aa: Affected
aa: Unaffected

Key Points

50% chance of passing the condition if one parent is heterozygous (Aa).
Family history is critical for diagnosis.

Examples

Achondroplasia
Huntington disease
Marfan syndrome
Familial hypercholesterolemia

2. Autosomal Recessive Inheritance

Characteristics

Males and females are equally affected.
Often due to enzyme deficiencies.
More severe than dominant disorders, with onset usually in childhood.
Common in consanguineous families.

Punnett Square Representation

Parent Genotype	A	a
A	AA	Aa
a	Aa	aa

AA: Unaffected
Aa: Carrier
aa: Affected

Key Points

With two carrier parents:
- 25% of offspring will be affected (aa).
- 50% will be carriers (Aa).
- 25% will be unaffected (AA).
Unaffected sibling of an affected individual has a 2/3 chance of being a carrier.

Examples

Cystic fibrosis
Phenylketonuria
Thalassemias
Wilson disease

3. X-Linked Recessive Inheritance

Characteristics

Males are more severely affected.
No male-to-male transmission.
Carrier mothers pass the condition to 50% of their sons.
Skips generations.

Punnett Square Representation

Mother Genotype	X	X
X (Father)	XX	XX
Y (Father)	XY	XY

XX (Carrier): Female carrier.
XY: Affected male.

Examples

Duchenne muscular dystrophy
Hemophilia A and B
G6PD deficiency

4. X-Linked Dominant Inheritance

Characteristics

Transmitted through both parents.
Affected mothers pass to 50% of sons and daughters.
Affected fathers pass to all daughters but not sons.

Punnett Square Representation

Parent Genotype	X	X
X (Father)	XX	XX
Y (Father)	XY	XY

XX: Affected female.
XY: Unaffected male.

Examples

Fragile X syndrome
Alport syndrome
Hypophosphatemic rickets

5. Mitochondrial Inheritance

Characteristics

Transmitted only through the mother.
All offspring of an affected female may show signs of disease.
Exhibits heteroplasmy, leading to variable expression even within a family.

Key Features

Often affects organs with high energy demand (e.g., muscles, CNS).
Muscle biopsy shows ragged red fibers.

Examples

Mitochondrial myopathies (e.g., MELAS syndrome).
Leber hereditary optic neuropathy (subacute vision loss).

Points to Remember

Autosomal Dominant: Structural defects; family history critical.
Autosomal Recessive: Enzyme deficiencies; often more severe.
X-Linked Recessive: Affects males; skips generations.
X-Linked Dominant: Passed by both parents; unique daughter/son transmission pattern.
Mitochondrial: Maternal inheritance; variable expression due to heteroplasmy.

Summary Table

Mode	Key Features	Examples
Autosomal Dominant	Structural defects, pleiotropic	Marfan syndrome, Huntington disease
Autosomal Recessive	Enzyme deficiencies, severe	Cystic fibrosis, Wilson disease
X-Linked Recessive	Affects males, skips generations	Hemophilia, Duchenne muscular dystrophy
X-Linked Dominant	Unique transmission to daughters/sons	Fragile X syndrome, Alport syndrome
Mitochondrial	Maternal inheritance, heteroplasmy	MELAS syndrome, Leber optic neuropathy

Bibliography

Genetics by Strachan and Read.
Online Mendelian Inheritance in Man (OMIM).
Medical Genetics by Jorde et al.

USMLE Step 1 Review Series

Curriculum

U01.01.048 Modes of inheritance

1. Autosomal Dominant Inheritance

Characteristics

Punnett Square Representation

Key Points

Examples

2. Autosomal Recessive Inheritance

Characteristics

Punnett Square Representation

Key Points

Examples

3. X-Linked Recessive Inheritance

Characteristics

Punnett Square Representation

Examples

4. X-Linked Dominant Inheritance

Characteristics

Punnett Square Representation

Examples

5. Mitochondrial Inheritance

Characteristics

Key Features

Examples

Points to Remember

Summary Table

Bibliography

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