Genetic architecture of behaviour

Genetic architecture of behaviour How many QTL? What is the average effect size of a QTL? How do the QTL act? What is the molecular basis of QTL action?

OFA App.- John & Gene

(From DeFries, Gervais and Thomas, 1978). OFA/OFD bar graph (From DeFries, Gervais and Thomas, 1978).

) (From DeFries, Gervais and Thomas, 1978). OFA line graph ) (From DeFries, Gervais and Thomas, 1978).

Inbred Strain Cross

Intercross experiment DeFries H1 X DeFries L1 815 animals DeFries H2 X DeFries L2 821 animals TOTAL: 1,636

Loci that influence variation in Open Field Activity

How many QTL?

Power to detect a locus

Undetectable QTL

QTL estimator

What is the effect size of the QTL?

Average Effect Size of QTL detected in studies of rodent behaviour

Average Effect Size

Genetic action How important are epistatic effects?

Interaction A1 A2 B1 B2 Phenotype 100 100

Interaction A1 A2 B1 B2 Interaction Phenotype 100 + 100 = 300

Epistasis: definition F-All: Y = b0 + b 1NA1 + b 2NB1 + b 3(NA1)(NB1) F-Part: Y = b0 + b 1NA1 + b 2NB1 NA1 is the "gene dosage" for the A1 allele in each genotype etc F-Int2,Fulldf2 = ((F-AllFss – F-PartFss)/F-AllRss)(F-Alldf1-F-Partdf1)/F-Aldf2))

Circadian Rhythm Interaction QTL

Interaction analysis All pairs of markers tested for interaction on 23 phenotypes total of 86,043 analyses

Interaction analysis All pairs of markers tested for interaction on 23 phenotypes total of 86,043 analyses 4,048 results gave a -LogP of > 6.7 (significance level for the likelihood under the full regression model (F-all))

Interaction analysis All pairs of markers tested for interaction on 23 phenotypes total of 86,043 analyses 4,048 results gave a -LogP of > 6.7 (significance level for the likelihood under the full regression model (F-all)) 0.05 threshold is –LogP 4.9

Interaction terms less than P-value 0.001 (LogP > 3)

Lung Cancer Susceptibility

Genetic architecture Up to 12 QTL Effect sizes < 10% No evidence for interaction

What is the molecular basis of the QTL?

QTL mapping of arthritis susceptibility in rats

Positional cloning of the QTL

Reasons for success Large effect size: ~25% of phenotypic variance Recognizable mutation

Increasing Generations F0 F1 F2 F3 F4

Two Strains

Eight Strains

Genetically Heterogeneous Mice A/J AKR Balb C3H C57 DBA IS RIII HS Random Breeding HS generations >50

High Resolution

Physical Map 141 147 145 143 149 Rgs1 Rgs13 Rgs18 Uch15 Rgs2 Cfh B3galt2 Ssa2 Glrx2 145 143 149

Coding sequence variants

Coding sequence variants None

Relation between Sequence Variants and Genetic Effect

Strain Sequences Must Be Consistent with QTL Action BALB AKR

Relation between Sequence Variants and Genetic Effect Marker 1 QTL Marker 2 No effect observable Observable effect

Strain pattern of sequence differences

Sequence variation

Strain Distribution

Rgs1 Rgs13 Rgs18 Uch15 Rgs2 B3galt2 Ssa2

Genes Rgs2 Rgs13 Rgs1 Rgs18

Regulators of G Protein signalling So what are RGS proteins? They are regulators of G protein signalling, that is to say they they regulate the formation of the heterotrimeric G protein that interacts with many cell surface receptors, including receptors for many neurotransmitters in the CNS. Therefore RGS proteins are potential candidates for contributing to variation in the behaviours we have been investigating How can we demonstrate that variation in the RGS2 gene is responsible for the QTL? Well one simple thing we can do is to exclude the gene, and this is

RGS2 Knock-out shows enhanced fear response

Markers s 1 m-1 m m+1 M Strains t