modes of inheritance Flashcards
- What are the key traits of a dominant autosomal disorder?
Single gene disease or trait passed down to offspring with multiple generations affected
Each affected child normally has one affected parent Each child of an affected person has a 1 in 2 chance of being affected
What is meant by a vertical pedigree pattern?
every generation affected
- How could make a genetic mutation dominant?
Mutations resulting from a DNA expansion of a CAG repeat on chromosome for example in Huntington’s disease it is on chromosome 4
- What are the three consequences a dominant autosomal disorder can incur?
Gain of function - Gene now makes a protein with a new function, e.g - longer lifespan or new location to increase effect
Dominant negative effect - Mutated form interferes with the activity of proteins it binds to, e.g - dimers reduce activity Insufficient - Mutant in one gene results in 1/2 amount of a protein that is not enough for normal function
- What is meant by an Autosomal Recessive Disorder?
- Why are carriers unaffected?
2 copies of recessive allele must be present in order for trait/disease to develop
Tend to be ‘loss of function’ mutations
Lost a single copy of a gene but the normal one is sufficient enough to maintain normal function
- What does a horizontal pedigree pattern show?
- What effect does consanguinity have on the occurrence of autosomal recessive disorders?
Affected individuals are often seen in more than one child in a family and not in all generations
Increases probability of occurrence
- Which sex does X-linked disorders (recessive) mainly affect and why?
- If a father is affected by X-linked dominant disorder, what will be the effects on the sons and daughters?
Males - only one X chromosome so it is effectively dominant
No sons will be affected
All daughters will be affected
- Why might X-linked dominant disorders affect males and females differently?
- What is usually an effect of X-linked dominant disorders?
Females can be less affected because the normal X gene may be active in some cells rather than the mutant gene
The process is called X inactivation and is random
Increase of current function
- What is meant by a Y-linked disorder?
- If a father is affected by a mitochondrial disease, what is the effect on the children?
Only affects males
All sons of an affected father are affected
None are affected Mitochondrial DNA will not be passed down by father, however if mother was affected, all the children would be affected
- What causes mitochondrial disease variability?
- What does the severity of symptoms depend on?
Random segregation of genes during binary fission so some mutant forms may be removed from a mitochondrion
Depends on the number of affected mitochondria as in the future more mutant mitochondria may accumulate to become a larger proportion of the mitochondria in the organism- develops with age
Example of X linked Recessive disease?
Example of autosomal dominant disease?
Example of mitochondrial disease?
Haemophilia, more frequent or severe bleeds, affects factors 8 or 9
Huntingtons
Lebers hereditary optic neuropathy - visual loss in young adulthood , degeneration of optic nerve and retina
Where else can mitochondrial diseases be inherited by
not always mitochondrial DNA
mutations in cell genome
or mendalian/ sex linked chromosomal inheritance
for an x linked recessive disease, what are the chances of the brother of an affected son from having the disorder
what are the chances of a sister of an affected person being a carrier
1/2
1/2
what do the severity of symptoms vary with in mitochondrial disease?
number of mitochondria
symptoms develop once threshold reaches
cells have different number of mutant mitochondria which changes with time
develop with age de to accumulation of mutant mitochondria
what function is usually impaired with mitochondrial diseases
motor and nerve function
