Patterns of Inheritence Flashcards
What type of inheritence pattern is Familial Hypercholesterolemia, Huntington’s disease Neurofibromatosis and Marfan syndrome?
Autosomal Dominant - Affecting Structural genes typically.
Name some autosomal dominant Conditions
Familial Hypercholesterolemia, Huntington disease, Marfan syndrome, Neurofibromatosis.
Describe Autosomal Dominant inheritence
Affected individuals have an affected parent.
Either sex is affected.
Variable to late onset typically.
What type of inheritance pattern do Sickle cell anaemia, Cystic Fibrosis, Phenylketonuria (PKU) and Kartagener syndrome all have?
Autosomal Recessive - Affecting genes encoding for enzymes.
What conditions have a Autosomal Recessive Inheritance pattern?
Sickle cell Anaemia, Phenylketonuria, Kartagener syndrome and Cystic Fibrosis.
Describe Autosomal Recessive Inheritence
Unaffected parents, Either sex is affected, Early/uniform onset, often for catalytic proteins,
Sometimes occurs in consanguity (incest)
What do Fragile X syndrome and Hypophosphatemic rickets (vitamin D resistant rickets) have in common?
X-Linked Dominant disorders
Describe the inheritence of X-lnked Dominant disorders
Males cannot pass onto sons.
Mothers transmit to 50% of offspring. Fathers to all daughters.
What type of inheritence is Duchenne Muscular dystrophy, G6PD deficiency, Lesch Nyhan syndrome, Ornithine transcarbamyase deficiency, Haemophilia A and B?
X-linked Recessive
What is a sign of Mitochondrial inheritence?
Transmitted through mothers,
Variable expression,
Mitochondrial myopathies –> ragged red fibres on muscle biopsy.
Define Codominance
Both alleles contribute to phenotye.
Examples of codominant conditions?
Blood groups A, B and AB,
Alpha-1-antitrypsin dificiency
What is Variable expressivity?
Phenotype varies among individuals with same genotype.
Examples of variable expressivity.
Neurofibromatosis type 1, patients may have varying disease.
What is Incomplete Penetrance?
Mutant genotype may not produce a mutant phenotype.
Example of incomplete penetrance?
BRCA 1 gene for breast cancer increases chances to 60% - not 100%.
What is Pleiotropy?
One gene contributes to multiple phenotypic effects.
Examples of Pleiotropy?
Untreated Phenylketonuria leads to light skin, intellectual disability, musty smell.
What is anticipation?
Increased severity of disease or earlier onset in succeding generations. HD.
What is Loss of Heterozygosity?
If patient inherits or develops a mutation in a TS gene, the complementary allele must acquire a mutation before cancer develops.
Examples of a loss of heterzygosity?
p53 and Retinoblastoma genes.
What is a Dominant negative mutation?
Heterozygote produces nonfunctioning altered protein that prevents normal gene product formation or function.
What is a Linkage disequillibrium?
Tendancy for two allels at 2 linked loci to occur together more or less often than expected by chance.
What is Mosicism?
Presence of genetically distinct cell lines in the same individual.
Somatic - where the mutation arises from mitotic errors after fertilisation and occurs throughout tissues.
Gonadal - Mutations occur in sperm of egg cells but not all.
Example of Mosaicism
McCune-Albright syndrome - Mutation affecting G-protein linked signalling.
What are some signs of McCune-Albright syndrome?
Unilateral cafe au lait spots, polyostotic fibrous dysplasia, precocious puberty, endocrine abnormalities.
What is Locus heterogenecity?
Mutations at different locations produce a similar phenotype. Albinism
What is Allelic heterogenecity?
Different mutations at the same locus lead to the same phenotype. Example is Beta-Thalassaemia.
What is Heteroplasmy?
Presence of both normal and mutated mtDNA lead to variable expression in mitochondrially inherited disease.
What is Uniparental disomy?
Offspring recieves 2 copies of a chromosome from one parent and no copies from the other. Typically normal phenotype but can manifest as affected with recessive disorder found in one parent.
Heterodisomy is where there is an error with what?
Meiosis I.
Isodisomy is where there is an error where?
Meiosis II or postzygotic chromosomal duplication of one set and loss of the other.
Prader-Willi syndrome and Angelman syndrome both have what in common?
Deletion of genes on chromosome 15, Typically brought out due to Maternal or paternal imprinting respectively.
