Seminar 3- types of single gene inheritance. traditional and non-traditional inheritance Flashcards
(28 cards)
Autosomal dominant inheritance
Mutated gene is a dominant gene located on one of the non-sex chromosomes (autosomes)
Autosomal recessive inheritance
Locus is on an autosome and 2 mutant alleles required for phenotype expression
X-linked dominant inheritance
Locus is on X-chromosome. only 1 mutant allele needed for expression in females
X-linked recessive inheritance
the locus is on x-chromosome and a female must carry both alleles for expression
Autosomal dominant inheritance basic criteria
- All affected children have at least 1 affected parent
- Any child of affected persons has a 50% risk of inheriting
- Unaffected family members don’t transmit the trait to their children
- Trait is not influenced by sex, both sexes likely to have and transmit the trait
Expressions of typical rules of inheritance
Variable expressivity Late onset Pleiotropy Incomplete penetrance Mosaicisms- Gonadal and Somatic De novo mutations
Variable expressivity
Range of signs and symptoms occuring in people with the same genetic condition
- the extent of expressions of the disease phenotype
Pleiotropy
the multiple phenotypic effects of a gene
Incomplete penetrance
Not all people carrying a mutated gene express the associated traits
De novo mutations
present for first time in a family member
- mutation occurs in parents germ cell
Mosaicism
the presence of 2 or more cell lines with diff genotypes in one individual who has developed from a single zygote
- due to error after conception
Gonadal mosaicism
mutation is present in part of a healthy parent’s germ cells
- Osteogenesis imperfecta
- achondroplasia
Somatic mosaicism
mutation occurs in early embryogenesis in a single somatic cell
- Marfan syndrome
- Neurofibromatosis type 1
Examples of autosomal dominant disorders
Marfan syndrome Huntington disease Neurofibromatosis type 1 AD polycystic kidney disease Osteogenesis imperfecta Achondroplasia
Autosomal recessive inheritance criteria
- Both parents are asymptomatic carriers with one normal and mutant allele
- condition typically appears in 1 generation only (siblings)
- 2 carrier parents have a 25% chance of having an affected child
- common in consanguineous marriages
- Each unaffected sibling of the affected individual has a 2/3 chance of being a carrier
Obligate carriers
Parents and offspring of an affected individual with AR disease
Locus heterogenity
- Cornelia de Lange syndrome
a single disorder caused by mutations in genes at different chromosomal loci
- only 1 mutant loci is needed for the phenotype to manifest
Allelic heterogenity
when there are different mutations at he same locus
Examples of Autosomal recessive disorders
Cystic fibrosis
Sickle cell anemia
Alpha and Beta -thalassemia
Spinal muscular atrophy
X- inactivation/ lyonisation
process by which one of the copies of the X chromosomes in females is inactivated
Criteria for X-linked dominance
Males affected more
- A female with an x-linked dom trait has a 50% chance of passing it to her children
- a male with the trait has a
X-linked recessive diseases
Red- green colour blindness
- Hemophilia
- Duchenne dystrophy
- Fabry disease
- Hunter syndrome
Chimera
Single organism composed of cells from different zygotes
- can have both male and female sex organs, 2 blood type cells
Mitochondrial/cytoplasmic inheritance
- through mitochondrial DNA inherited only from maternal
- has a higher rate of spontaneous mutations
