Genotype, phenotype and inheritance part 2 Flashcards
Give an example of X-linked dominant inheritance
Fragile X syndrome - asscoaited with intellectual disability and autism and caused by a change in structure of X chromosome
Who is affected by X-linked dominant inheritance?
Hemizygous males (XY)
Heterozygous and homozygous females - only needed on one X
Can affected males give a trait to their sons in X-linked dominant inheritance?
No, because sons will only inherit Y chromosomes
In heterozygous carrier females, what is the chance of them having affected offspring in X-linked dominant inheritance?
50% chance
How is mitochondrial DNA inherited? What does this mean?
Passed via maternal line
Affected mother will always give rise to affected children, but unaffected mother never does, despite genotype of father
Example of a disease linked to mitochondrial DNA
Kaerns-Sayer syndrome - reduction of heart, eye and muscle movements
What is polygenic inheritance?
Phenotypes are influenced by multiple genes
Give an example of a polygenic trait
Albinism - human skin colour
Will two homozygous recessive albino parents of A gene always give albino offspring?
No, despite being recessive, albinism is polygenic so is controlled by multiple genes
What gene is albinism caused by?
Two paralogues of Agene - A1 and A2 (and alleles a1 a2)
When is albinism caused in the A genes?
When either gene is homozygous recessive - so either a1a1 or a2a2
Does a single gene often cause a phenotype?
No, multiple genes act together- usually a disease is triggered when a threshold is passed (common variants with small effect but come together)
What is genome wide association used to do?
Study complex diseases and find SNP’s that occur more often in disease carriers
What does a genome wide association study graph show us?
Shows the SNP’s that pass the threshold to help trigger a disease - in order to inherit the disease you would have to inherit all variants that pass the threshold
3 limitations of GWAS (genome wide association stud)
- Large sample size needed to reach statistical significance - hard for rare diseases
- Correlation does not equal causation - follow up studies needed
- Not all SNP’s are in coding genes
