Inheritance Patterns - types, traits and mutations

Inheritance Patterns - types, traits and mutations

Inheritance Patterns - the ways in which genotypes pass among individuals and generations. Many inherited traits are either autosomal or Xlinked and either dominant or recessive. Such inheritance patterns reflect statistical calculations assessing the mathematical likelihood of certain traits or mutations passing from one generation to the next. Inheritance patterns consider the genotypes of each parent. Inheritance patterns vary according to whether the chromosomes responsible are autosomesal or sex-linked chromosomes. Geneticists often refer to these patterns as Mendelian, in reference to the foundational work of botanist Gregor Mendel (1822–1884), who was the first to delineate inheritance patterns.

Recent research, notably through the HUMAN GENOME PROJECT, has shown that much of human inheritance may not be quite so simple as the Mendelian model. Multiple genes and chromosomes share responsibility for traits ranging from EYE color to the development of diseases, such as DIABETES AND CARDIOVASCULAR DISEASE, that also have environmental (lifestyle) components. This circumstance of multiple factors makes it far more difficult to statistically represent a delineated pattern of inheritance. Multifactorial inheritance is not clearly dominant or recessive, though is commonly autosomal (derives from autosomes rather than sex chromosomes).

The least common pattern of inheritance is mitochondrial, which comes only from the mother and involves traits and mutations affecting mitochondrial, not nuclear, DNA. This pattern is exclusively maternal because only the ovum (female GAMETE or egg) contains mitochondria. Mitochondria affect functions rather than structures of the body, and thus, mitochondrial mutations cause numerous, nonspecific multisystem disturbances. Because mitochondria are the energy generators of the cells, mitochondrial mutations affect functions that require energy rather than affect structures of the body. Though mitochondrial mutations may be single-GENE, they often have widespread effects across types of cells in which energy needs are high, such as NERVE cells and MUSCLE cells.

Inheritance Patterns: Autosomal Traits and Mutations
Autosomal RecessiveAutosomal Dominant
Both parents carriers One parent carrier, one parent noncarrier Both parents affected One parent affected, one parent unaffected
Each child:
  - 25% condition
  - 25% noncarrier
  - 50% carrier
Each child:
  - 50% noncarrier
  - 50% carrier
Each child:
  - 25% unaffected
  - 25% more severely affected
  - than parents
  - 50% affected
Each child:
  - 50% unaffected
  - 50% affected

Percentages refer to the probability of occurrence.

Inheritance Patterns: X-Linked Traits and Mutations
X-Linked RecessiveX-Linked Dominant
Mother CARRIER,
father noncarrier
Each daughter:
25% noncarrier
25% carrier
Each son:
25% noncarrier
25% affected
Mother noncarrier,
father affected
Each daughter:
100% carrier
Each son:
100% noncarrier
Mother affected,
father noncarrier
Each daughter or son:
50% affected
50% nonaffected
Mother noncarrier,
father affected
Each daughter:
100% affected
Each son:
100% nonaffected

Percentages refer to the probability of occurrence.

See also AUTOSOME; CHROMOSOME; FAMILY MEDICAL PEDIGREE; GENOTYPE; MITOCHONDRIAL DISORDERS; MITOCHONDRIAL DNA (MTDNA); MUTATION; SEX CHROMOSOME.

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Genetics and Molecular Medicine

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