Hoffman Hobag Flashcards
Field patterns for traits –>
genetic basis? –> adaptation or population process –> allele association, lab selection studies, QTL mapping, microarray
Polymorphisms for trait
Many in a genome: limited number of genetic changes with PHENOTYPIC EFFECTS .e.g. duplication (gain of function)
look for exons (conserved)–> promoters
Deca polymorphism
Decrease size, increase towards tropics
Overexpression decreases size through gal 4
Repeatable cline
Neutral alleles
Do not show clines
Improving experiment? worthwhile?
Look at different species
Conserve evolutionary potential
Increase population size to stop drift (10^4) - don’t want to lose genetic variation –> dont want to lose evolutionary potential
Heritability for physiological traits
Measure QTL by measuring heritability
e.g. heat resistance 0.3-0.5, dessication resistance in insects >0.5, cold resistance in mice 0.2-0.5i
Response to selection
R=H^2 x S
Heritability high –> response
heratbility =0 –
> no response
Birchii
Very little variation at any locus - bottlenekc?
Microsatellite results: average H level (0.65=normal),
A is high
Don’t know candidate loci
Genetic diversity & adaptation
Selection acts on variation and variation with a genetic basis
pgi gene in butterflies
Gives allozymic gene product
Different rates of activity at different temperatures
Heterozygotes most active at cooler temps
Genetic polymorphisms
Need a genome wide scan for polymorphisms across time and space
REPLAYING THE TAPE (repeat): to verify observed is not product of drift &
replicate across species (Fst to analyse outliers)
Vp=Vg+Ve=(Va+Vd+Vi) + Ve
Va: additive variation (resemblance across generations - major determinant of how well organisms responds to selection)
Vd: dominance variance (offspring resemble siblings)
Vi: Interactive variance (interactions between loci)
If gene shows mostly additive variation:
F1:trait value intermediate to parents
F2: same mean as F1 but greater variance
If trait shows dominance:
F1: resemble only 1 parental strain
F2: same mean as F1, greater variance
Heritability
Measure of variation
Measures proportion of variation due to genetic factors and how well population can respond to selection
If alleles controlling trait are fixed in population, H=…
H=0, no variation to pass on
Narrow sense heritability
h2=Va/(Vg+Ve)= measure of heritability and how well population can respond to selection
Breeder’s equation
R=h2S - estimates heritability from selection experiments Graph midoffspring(y) and midparent (x) - slope = h2 1 parent: b=1/2h2, grandparent: b=1/4h2 If graph is random scatter, heritability=0
Fitness traits have ____heritability
LOW
Genotype/environment interactions
Heritability is not constant e.g. height depends on nutrient availability
Common garden experiment
Determine if traight variation is genetic or environmental
Individuals from populations that existed in diff environments and SWAP
Cross over: environmental
No cross: genetic
Pleiotropy
One gene affecting multiple traits
If gene affects more than one trait…
Selection might be acting one one of the traits, but the other traits will change in a parallel manner
