R13 complex traits Flashcards
What is different about the pigmentation of siamese cats ?
The enzymes are activated at different temperatures so more or less pigment gets produced at hotter or colder areas
What is penetrance
: the proportion of individuals with a given genotype that shows an “expected” phenotype.
What is expressivity ?
the degree of gene expression (could be influenced by the environment)
What is eugenics ?
limit reproduction of a certain groups in a population, filtering the population
- Forced sterilisation
- Concentration camps
This is providing that all traits are genetic even poverty and alcoholism. Which isn’t the case.
What is the difference of additive effects vs dominance ?
- Additive effect – the combination of alleles adds up to make the phenotype
- Dominance – non-additive allelic interaction, heterozygotes and homozygote dominance are identical
What is broad-sense heritability ? (H^2)
the proportion of phenotypic variance due to genetics. Trait, population and environment specific
What does phenotypic variation equal ?
Variation due to genetic components (H^2) + variation due to environment and error
If identical twins are separated at birth and brought up in different environments, what effect does that have on broad-sense heritability ?
greater value of broad-sense heritability.
What is narrow-sense heritability (h^2)?
Dominance interactions in the parents cannot be inherited to the offspring, as alleles are inherited not genotypes.
- Variation due to additive genetic components is narrow-sense heritability h2
Variation due to genetic components (h2) = variation due to additive genetic component (h2) + variation due to non-additive genetic components.
Narrow sense heritability represents the proportion of genetic variation in a trait that can be inherited. It excludes non-additive effects and the contribution of the environment.
What is the selection differential (S) ?
difference between means of selected group and base population
What is response differential (R)?
difference between means of offspring and base population
What does H^2 equal in terms of S and R ?
R/S
H is between 0 and 1
What is Quantitate trait loci (QTLs)?
Genomic regions that control the genetic variation of a complex trait, each allele has a small contribution to the phenotype
- Cannot be determined only using the phenotype, statistics are needed.
What is QTL mapping ?
two lines that differ at a known marker loci
How can we produce a QTL map ?
- Cross the F1 individuals and correlate the phenotype to genetic make-up in F2 (sequence marker regions)
- Some markers segregate more frequently with the trait of interest, others will not show a correlation.
Associated markers not causative of the train or within the QTL itself
The mapping identifies a broad genomic region where the QTL is likely to sit
What is a genome wide association scan (GWAS) ?
no need for controlled crosses of specific lines, we can use a natural population.
- Asses many alleles at once
- More recombination would have happened over time in a population compared to an individual
- Many markers needed
- Creates a narrower genomic region for a QTL
- Only suitable for common variants not rare ones.
What is linkage disequilibrium ?
degree to which one genetic variant is inherited (or correlated) with a nearby genetic variant (allele) in a given population
- Co-inheritance of QTL allele and markers is an example, these are partial linkage disequilibrium
- Recombination goes against this concept
What is some disadvantages of QTL ?
QTL will overestimate the h2 of rare variants, non-additive effects and environmental components won’t be detected, sample size/ power failing to pick up QTLs
same QTL might appear in multiple GWAS for different complex traits, same or different allelic variants for that QTL might be involved.
What is pleiotropy?
a single locus affects two or more distinct phenotypic traits, highly common
What can be identified in GWAS ?
SNPs (single nucleotides polymorphism), deletions and insertions would not be picked up
Are all complex traits continuous ?
No, complex diseases are a thing
How much DNA do siblings share?
50%
What is the difference between clinical and direct-to-consumer genetic testing ?
Direct-to-consumer genetic testing: only sequence a region of your genes, so a negative result shows you don’t carry a common variant associated with that condition.
Clinical testing: sequence the entire gene
