R13 complex traits

Question 1

What is different about the pigmentation of siamese cats ?

Answer 1

The enzymes are activated at different temperatures so more or less pigment gets produced at hotter or colder areas

Question 2

What is penetrance

Answer 2

: the proportion of individuals with a given genotype that shows an “expected” phenotype.

Question 3

What is expressivity ?

Answer 3

the degree of gene expression (could be influenced by the environment)

Question 4

What is eugenics ?

Answer 4

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.

Question 5

What is the difference of additive effects vs dominance ?

Answer 5

• Additive effect – the combination of alleles adds up to make the phenotype
• Dominance – non-additive allelic interaction, heterozygotes and homozygote dominance are identical

Question 6

What is broad-sense heritability ? (H^2)

Answer 6

the proportion of phenotypic variance due to genetics. Trait, population and environment specific

Question 7

What does phenotypic variation equal ?

Answer 7

Variation due to genetic components (H^2) + variation due to environment and error

Question 8

If identical twins are separated at birth and brought up in different environments, what effect does that have on broad-sense heritability ?

Answer 8

greater value of broad-sense heritability.

Question 9

What is narrow-sense heritability (h^2)?

Answer 9

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.

Question 10

What is the selection differential (S) ?

Answer 10

difference between means of selected group and base population

Question 11

What is response differential (R)?

Answer 11

difference between means of offspring and base population

Question 12

What does H^2 equal in terms of S and R ?

Answer 12

R/S

H is between 0 and 1

Question 13

What is Quantitate trait loci (QTLs)?

Answer 13

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.

Question 14

What is QTL mapping ?

Answer 14

two lines that differ at a known marker loci

Question 15

How can we produce a QTL map ?

Answer 15

• 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

Question 16

What is a genome wide association scan (GWAS) ?

Answer 16

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.

Question 17

What is linkage disequilibrium ?

Answer 17

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

Question 18

What is some disadvantages of QTL ?

Answer 18

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.

Question 19

What is pleiotropy?

Answer 19

a single locus affects two or more distinct phenotypic traits, highly common

Question 20

What can be identified in GWAS ?

Answer 20

SNPs (single nucleotides polymorphism), deletions and insertions would not be picked up

Question 21

Are all complex traits continuous ?

Answer 21

No, complex diseases are a thing

Question 22

How much DNA do siblings share?

Answer 22

50%

Question 23

What is the difference between clinical and direct-to-consumer genetic testing ?

Answer 23

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