inheritance pattern Flashcards
What are pedigree drawing symbols?
=> square = male => circle = female => line between = partners => line above = siblings => 2 branch = twins => line down = children => shaded = affected => dots = carriers => crossed shape = dead => diamond = still birth(SB), pregnant (p), => empty diamond = unknown sex of baby =>triangle = miscarriage => triangle with cross = abortion.
consanguineous couple:
double line joins partners
=> first cousins couple.
What are characteristics of inheritance patterns of autosomal dominant?
- manifest in heterozygous form
- multiple generations affected (but if individual’s siblings or children not affected then can not pass it to their offspring).
- both sexes affected
- male to female and female to male transmission
- most will have an affected parent (but sometimes it can be a random mutation)
- 50% risk of offspring
Define penetrance.
- percentage of individuals who carry the mutation AND develop symptoms of the disorder
=> many dominant disorders show age- dependent penetrance
What are features of autosomal dominant inheritance?
=>VARIABLE EXPRESSIVITY
variation in severity/symptoms of disorder between individuals with same mutation
=> NEW MUTATION RATE.
de novo mutation rate varies between autosomal dominant conditions.
=> SOMATIC MOSAICISM
new mutation arising at early stage in embryogenesis - present in only tissues/ cells
=> GERM LINE MOSAICISM (GONADAL)
new mutation arises during oogenesis or spermatogenesis - mutation present in gametes can be transmitted to offspring
=> ANTICIPATION
worsening or disease severity in successive generations, characteristically occurs in triplet repeat disorder
What are characteristics of autosomal recessive inheritance?
-manifest in homozygous/ compound heterozygous form
- carriers (heterozygous) not affected
- both sexes affected
male to female and female to male transmission
- usually one generation affected
- could be consanguinity
What are features of autosomal recessive inheritance?
- trait often found in clusters of siblings but not in parents and offsprings
- reoccurrence risk = 1/4 for each siblings of affected person
- carriers probability = 2/3 for unaffected siblings of affected person
- all offspring of affected person are OBLIGATE CARRRIERS
what are features of X - linked inheritance?
- recessive : women are carriers + unaffected
- dominant : women are affected , males are more severely affected bc they dont have a back up X
What are aspects of X - linked recessive inheritance?
- x linked genes never passed from father to son
- all daughters of affected males are obligate carriers
- children of carriers females have 50% chance of inheriting mutant allele
Define skewed X - inactivation.
generally random but ~ 10% of women have uneven or skewed X - inactivation
Define manifesting carriers.
some women have some symptoms in X -linked recessive conditions e.g. cardiomyopathy in DMD
What the 3 main types of mutations?
- substitutions (point mutations)
- deletions
- insertions
What is synonymous (silent) base substitution?
- mutation makes no difference because both codon codes for the same amino acid.
=> degeneracy
What is point (missense) mutation?
- replacement of a single base leads to incorrect amino acid being codes => malfunctioning protein.
Why does missense mutation not always lead to malfunctional protein?
- depends where the mutation is , if at the end of sequence doesn’t make much difference
- depends what protein is being coded (functional role) if the two proteins are similar then function isnt that affected.
- is it conserved bc if it is then it is important as it has been selected through evolution so it is important.
What is in frame insertion/deletion?
- multiple of 3 so 3, 6, 9 etc
- not damaging bc it doesn’t change reading frame, codons are read in 3s.
