Non-Mendelian Inheritance Overview

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Questions and Answers

Which condition is characterized by myopathy, lactic acidosis, and stroke-like episodes?

  • Leigh Syndrome
  • MELAS (correct)
  • Kearns-Sayre syndrome
  • MERF

What type of mutations are commonly associated with Pearson Syndrome?

  • Large deletions (correct)
  • Heteroplasmic mutations in ATPase
  • Homoplasmic mutations in rRNA
  • Point mutations in tRNA

Which disorder is linked to mutations in the 12S rRNA gene?

  • Leigh Syndrome
  • MELAS
  • Deafness (correct)
  • Kearns-Sayre syndrome

What inheritance pattern is most likely associated with the majority of mitochondrial disorders?

<p>Maternal inheritance (B)</p> Signup and view all the answers

Which of the following is a common congenital malformation associated with multifactorial inheritance?

<p>Congenital heart defects (B)</p> Signup and view all the answers

What is a consequence of reduced penetrance in genetic inheritance?

<p>Symptoms of the condition may not appear even if the genotype is present. (D)</p> Signup and view all the answers

Which of the following best describes 'variable expressivity'?

<p>Differences in severity of symptoms among individuals with the same genotype. (B)</p> Signup and view all the answers

What is a unique characteristic of mitochondrial disorders?

<p>Inheritance is primarily maternal due to mitochondrial DNA coming from the oocyte. (D)</p> Signup and view all the answers

In what way does uniparental disomy affect genetic inheritance?

<p>It can result in imprinting disorders due to inheriting two copies of a chromosome from one parent. (C)</p> Signup and view all the answers

Which of the following describes the concept of 'anticipation' in genetic disorders?

<p>Increased severity of symptoms with each successive generation. (A)</p> Signup and view all the answers

What distinguishes co-dominancy from traditional dominant and recessive inheritance?

<p>Both alleles are fully expressed in the phenotype of heterozygotes. (A)</p> Signup and view all the answers

How can mosaicism affect the expression of genetic disorders?

<p>It can lead to a milder form of the disorder in some tissues. (D)</p> Signup and view all the answers

Which statement about genomic imprinting is true?

<p>The expression of certain genes depends solely on whether they are inherited from the mother or the father. (D)</p> Signup and view all the answers

What is the significance of homoplasmy and heteroplasmy in mitochondrial genetics?

<p>Heteroplasmy indicates a mixture of normal and mutated mitochondria within cells. (A)</p> Signup and view all the answers

Flashcards

Non-Mendelian Inheritance

Inheritance patterns that do not follow Mendel's laws, including exceptions to Mendelian inheritance and other mechanisms like epigenetics, imprinted genes, and mitochondrial inheritance.

Reduced Penetrance

A genotype may not always produce the expected phenotype.

Variable Expressivity

The severity or presentation of a genetic trait can vary among individuals with the same gene.

Codominance

Both alleles of a gene pair are fully expressed.

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Skewed X inactivation

One X chromosome is inactivated more frequently than the other in females, leading to different expression of X-linked traits.

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Epigenetics

Changes in gene expression without altering the DNA sequence.

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Genomic Imprinting

Phenotype depends on whether the gene is inherited from the mother or the father.

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Imprinting Disorders

Disorders caused by abnormal genomic imprinting.

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Uniparental Disomy (UPD)

A condition where an individual inherits both copies of a chromosome from one parent.

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Triple Repeat Disorders

Conditions caused by expansions of a specific DNA sequence with repeated units.

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Mosaicism

Presence of two or more genetically distinct cell lines in the same individual.

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Mitochondrial Disorders

Conditions caused by mutations in mitochondrial DNA.

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Multifactorial Inheritance

Inheritance pattern where the phenotype is influenced by both genetic and environmental factors.

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Homoplasmy

A condition where all mitochondria in a cell contain the same mtDNA.

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Heteroplasmy

A condition where a cell contains a mixture of both normal and mutated mtDNA.

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Replicative Segregation

Random distribution of mitochondria (carrying their different mtDNA) during cell division.

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Mitochondrial Disorders

Genetic diseases caused by mutations in mitochondrial DNA, often exhibiting heteroplasmy and maternal inheritance.

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ATPase subunit 6 gene mutations

Mutations in the ATPase subunit 6 gene linked to certain neurological disorders like Leigh syndrome.

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Leigh Syndrome

Progressive neurodegenerative disorder linked to mutations in the ATPase subunit 6 gene, showing maternal inheritance and heteroplasmy.

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MELAS

Mitochondrial disorder causing myopathy, lactic acidosis, and stroke-like episodes due to tRNAleu (UUR) mutations, with maternal inheritance and heteroplasmy.

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MERF

Mitochondrial disorder causing myoclonic epilepsy and ragged red muscle fibers, linked to tRNAlys mutations, exhibiting maternal inheritance and heteroplasmy.

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Deafness (Progressive Sensorineural)

Progressive deafness due to 12S rRNA mutations, showing maternal inheritance and homoplasmy.

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Pearson Syndrome

Mitochondrial disorder with pancreatic insufficiency, sometimes with mutations, large deletions in mtDNA, displays heteroplasmic inheritance, most often maternal.

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Kearns-Sayre Syndrome

Mitochondrial disorder causing myopathy, heart block, and ataxia, featuring 5 kb deletions in mtDNA, sporadic cases also involving somatic mutations.

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Multifactorial Inheritance

A mode of inheritance for diseases influenced by multiple genes and environmental factors.

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Multifactorial Diseases

Diseases resulting from a combination of genetic predispositions and environmental factors.

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Study Notes

Non-Mendelian Inheritance

  • Exceptions to Mendelian Inheritance:

    • Epigenetics
    • Genomic Imprinting and Imprinting Disorders
    • Uniparental Dysomy
    • Triple Repeat Disorders
    • Mosaicism
    • Mitochondrial Disorders
    • Multifactorial Inheritance

  • Reduced Penetrance:

    • Phenotypically normal family members may not transmit the phenotype to their children
    • Exceptions to typical Mendelian Inheritance patterns
    • Variable expressivity
      • Incomplete penetrance (graphics showing individuals with same genotype but different phenotypes)

  • Variable Expressivity:

    • Individuals with the same genotype may have different phenotypes
    • Shows a wide range of severity among affected individuals
    • Illustrated with specific conditions (e.g., neurofibromatosis)

  • Co-dominance:

    • Blood type inheritance: A, B, AB, O are codominant alleles
    • Both alleles are expressed

  • Skewed X Inactivation:

    • In X-linked recessive disorders, affected females can occur
    • Due to an uneven inactivation of the X chromosome

  • Genomic Imprinting:

    • Genes expressed differentially based on parental origin
    • Impacts traits like Prader-Willi syndrome and Angelman syndrome
    • Both disorders are linked to the same region on chromosome 15

  • Uniparental Disomy:

    • Offspring inherit two copies of a chromosome from one parent
    • Can lead to disorders

  • Triple Repeat Disorders:

    • Associated with expansions in specific triplet repeats in genes
    • Examples include Fragile X syndrome, Huntington's disease, and myotonic dystrophy
    • Genetic anticipation( earlier onset and increased severity) is a key aspect of these disorders

  • Mosaicism:

    • Presence of different cell lines within an individual due to cell division errors
    • Can affect single-gene disorders
    • Types: Somatic, germline, and combined mosaicism

  • Mitochondrial Disorders:

    • Inherited maternally
    • Caused by mutations in mitochondrial DNA(mtDNA)
    • Different mtDNA levels and variants cause different tissue and phenotypic manifestations

  • Multifactorial Inheritance:

    • Caused by a combination of genetic and environmental factors
    • Examples include congenital heart defects, neural tube defects, pyloric stenosis, and common diseases
    • Environmental factors affect phenotype based on genetic predisposition
    • Single nucleotide polymorphism(SNP) are a type of genetic variant that is common within the population

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