Genetic basis of complex inheritance Flashcards
Describe mechanisms of non-Mendelian inheritance.
Non-Mendelian inheritance involves genetic patterns that do not follow traditional dominant and recessive rules. Key mechanisms include:
Mitochondrial Inheritance: Genes in mitochondria are inherited only from the mother. Example: Leber’s hereditary optic neuropathy.
Genomic Imprinting: The expression of certain genes depends on whether they are inherited from the mother or father. Example: Prader-Willi syndrome (father’s allele) and Angelman syndrome (mother’s allele).
X-Inactivation: In females, one of the two X chromosomes is randomly inactivated, leading to mosaic gene expression. Example: Calico cats.
Anticipation: Some genetic disorders, like Huntington’s disease, worsen in severity or appear earlier in successive generations due to repeat expansions in DNA.
Extranuclear Inheritance: Inheritance of mitochondrial or plastid DNA, typically passed maternally. Example: Mitochondrial diseases.
Uniparental Disomy (UPD): Both copies of a chromosome come from one parent, leading to disorders, particularly when imprinted genes are involved. Example: Prader-Willi syndrome.
Epigenetic Inheritance: Heritable changes in gene expression without altering the DNA sequence, influenced by environmental factors. Example: Behavior changes in animals due to epigenetic modifications.
Hybrid Vigor: Offspring from crossbreeding often show enhanced traits compared to parents, known as heterosis. Example: Mules (horse-donkey hybrids).
Describe what is meant by penetrance.
Penetrance refers to the likelihood that individuals with a specific genetic mutation will show symptoms or traits associated with the condition.
Complete Penetrance: 100% of individuals with the mutation exhibit the condition (e.g., Huntington’s disease).
Incomplete Penetrance: Not all individuals with the mutation show symptoms (e.g., BRCA mutations for breast cancer).
Factors influencing penetrance include age, environment, genetic background, and sex. Penetrance is different from expressivity, which refers to the severity or variability of the condition in affected individuals.
Appreciate the role of the environment in genetic disease
The environment plays a significant role in the expression and progression of genetic diseases. Key ways in which the environment interacts with genetic factors include:
Gene-Environment Interactions: Environmental factors can modify how genetic diseases manifest. For example, cystic fibrosis symptoms may worsen with exposure to pollutants, and PKU severity can be controlled through diet.
Multifactorial Diseases: Diseases like cancer and type 2 diabetes result from both genetic predisposition and environmental influences (e.g., smoking, diet, stress).
Rare Genetic Disorders: Environmental factors such as dehydration or cold exposure can trigger or worsen symptoms of conditions like sickle cell disease and hemophilia.
Epigenetics: Environmental factors (e.g., diet, toxins) can cause changes in gene expression without altering the DNA sequence, potentially influencing disease risk and severity.
Aging and Environmental Impact: Age-related environmental exposures can accelerate genetic disease progression, such as in Alzheimer’s disease, where lifestyle factors play a role.
Prevention and Management: Lifestyle changes, like exercise and diet, can help prevent or manage genetic diseases by modifying environmental exposures.
In conclusion, genetics and environment work together to shape health outcomes, making it essential to consider both when managing and preventing genetic diseases.
