Monogenic inheritance Flashcards
Definition of monogenic inheritance?
Inheritance of characteristic through single gene
What are Mendel’s 3 laws of inheritance?
- Law of dominance- principle of dominant & recessive
- Law of segregation- only 1 allele for each train is passed to offspring- segregation of alleles occur when gametes formed
- Law of independent assortment- traits are inherited separately from each other- seed shape has no impact on seed colour
What are the 6 major modes of monogenic inheritance?
Autosomal dominant inheritance
autosomal recessive inheritance
x-linked dominant inheritance
x-linked recessive inheritance
y- linked inheritance
mitochondrial inheritance
Autosomal dominant- When is offspring affected by disease? Chnace that child inherits disease?
Affected offspring occur when 1 parent has the affected heterozygote, Aa.
- Affected parent can either pass on the disease allele, A or the normal allele, a.
50% chance of being affected (heterozygote) & 50% of being unaffected (homozygote)
*look at punnet square on notes
Autosomal dominant- what pattern does it show on pedigree diagram?
No skipping of generations
Vertical transmission
2 sexes affected equally
Father-to-son transmission - rules out condition being X-linked.
One parent must have the disease for it to be passed on.
Autosomal dominant- examples of conditions?
- Huntington’s disease
- Marfan Syndrome
- Postaxial Polydactyl
- Autosomal Dominant … Ataxias
Autosomal dominant- recurrence rate?
50%
recurrence rate- probability of future child being affected by disease
Autosomal recessive: when is offspring affected by disease? What is chance individual gets disease?
Parents are usually both heterozygous carriers, Aa.
25%chance if both parents are carriers.
*look at punnet square on notes
Autosomal recessive: pattern of inheritance shown on pedigree diagram?
Not seen generation-to-generation
Horizontal transmission - seen in siblings
Sexes affected equally
Consanguinity (related people) is present more often
*look at pedigree diagram on notes
Autosomal recessive- examples of conditions?
- Cystic fibrosis
- Sickle cell anaemia
- Albinism
Autosomal recessive- recurrence rate?
- 25% for Aa & Aa (2 carriers)
- 50% for Aa & aa (1 carrier & 1 with disease)
X-linked dominant inheritance- when is offspring affected? Impact of Affected mother & affected father?
If female inherits 1 normal copy & 1 faulty copy of gene- will be enough to cause the condition.
If male inherits faulty X chromosome- causes the condition.
- An affected male - 100% daughters will be affected & all sons will be unaffected
- Affected female- 50% chance of having affected children, both males & females
Daughters may have disease more mildly than sons because second X chromosome may reduce the impact of the diseased X gene.
- draw punnet squares to workout %
X-linked dominant inheritance: what pattern does it show on pedigree diagram?
Vertical transmission
Affected individuals predominantly female- as men can only pass affected X allele to daughters
Father to son transmission impossible
*Look at pedigree diagram on notes
X-linked dominant inheritance: examples of conditions?
Fragile X syndrome
Rett syndrome
X-linked recessive inheritance: Which offspring affected? What is chance they will get disease? What if mother & father affected (separately)?
Usually only affects males
Female carrier- will pass on either faulty or normal x chromosome- so 50% chance of developing disease & 50% chance of being healthy for sons, & 50% chance of inheriting faulty gene & becoming carrier & 50% chance of being health for daughters.
Affected male- son will never inherit faulty gene as men always pass Y chromosome to sons. Daughter will inherit faulty gene as men only have 1 X chromosome- all daughter become carriers
