Human Anatomy
Patterns of Inheritance
Patterns of inheritance for MBBS: autosomal dominant and recessive, X-linked and multifactorial inheritance with pedigree charts and disease examples, mapped to NMC codes AN74.1 to AN74.4.
MedNext Academy | 3 min read
Patterns of Inheritance
Patterns of inheritance for MBBS: autosomal dominant and recessive, X-linked and multifactorial inheritance with pedigree charts and disease examples, mapped to NMC codes AN74.1 to AN74.4.
This chapter explains the Mendelian and multifactorial patterns of inheritance with examples and the construction of pedigree charts. It gives the genetic basis of several important inherited diseases.
High-yield: Patterns of Inheritance
- The main Mendelian patterns are autosomal dominant, autosomal recessive, X-linked recessive and X-linked dominant.
- In autosomal dominant inheritance one copy of the faulty gene causes disease and the trait appears in every generation.
- Autosomal dominant conditions affect males and females equally and show male-to-male transmission.
- Achondroplasia and Marfan syndrome are examples of autosomal dominant inheritance.
- In autosomal recessive inheritance two faulty copies are needed, so parents are usually unaffected carriers.
- Cystic fibrosis and most inborn errors of metabolism are autosomal recessive.
- Consanguineous marriage increases the risk of autosomal recessive disease in the offspring.
- In X-linked recessive inheritance males are affected and females are usually carriers.
- There is no male-to-male transmission in X-linked inheritance because a father passes his Y, not his X, to his sons.
- Haemophilia and Duchenne muscular dystrophy are classic X-linked recessive disorders.
- In X-linked dominant inheritance, seen in vitamin D resistant rickets, affected fathers transmit to all daughters and no sons.
- A pedigree chart uses squares for males, circles for females and shaded symbols for affected individuals.
- Multifactorial inheritance results from several genes acting with environmental factors and does not follow simple ratios.
- Neural tube defects, cleft lip and many common diseases show multifactorial inheritance.
- Mitochondrial disorders are inherited only from the mother because the ovum contributes the mitochondria.
Inheritance patterns and examples
- **Autosomal dominant:** Every generation, sexes equal, male-to-male transmission. Achondroplasia, Marfan syndrome.
- **Autosomal recessive:** Two faulty copies, carrier parents, more with consanguinity. Cystic fibrosis.
- **X-linked recessive:** Males affected, female carriers, no male-to-male transmission. Haemophilia, Duchenne dystrophy.
- **Multifactorial:** Genes plus environment, no simple ratios. Neural tube defects, cleft lip.
NMC competencies in this chapter
- **AN74.1:** Modes of inheritance with examples
- **AN74.2:** Pedigree charts for the types of inheritance and example diseases
- **AN74.3:** Multifactorial inheritance with examples
- **AN74.4:** Genetic basis and features of achondroplasia, cystic fibrosis, vitamin D resistant rickets, haemophilia and Duchenne muscular dystrophy
Frequently Asked Questions
How do autosomal dominant and recessive inheritance differ?
In autosomal dominant inheritance one faulty gene copy causes disease, so the trait appears in every generation. In autosomal recessive inheritance two faulty copies are needed, so unaffected carriers can have affected children.
Why is there no male-to-male transmission in X-linked disorders?
A father passes his Y chromosome, not his X, to his sons, so an X-linked gene cannot go from father to son. Sons receive their X from the mother.
What is multifactorial inheritance?
It is inheritance determined by several genes acting together with environmental factors. It does not follow simple Mendelian ratios and underlies conditions such as neural tube defects and cleft lip.
How is a pedigree chart read?
Squares represent males, circles represent females, and shaded symbols represent affected people. The pattern of affected individuals across generations helps identify the mode of inheritance.
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