Crop Evolution Flashcards
what are the stages of crop domestication?
onset of domestication
in situ increase in frequency of desirable alleles
formation of cultivated populations that are adapted to enviornments and local preferences
deliberate breeding
how is selection used?
domestication can bottleneck
selection directly fixes genetic loci responsible for domestication traits
artificial selection reduces genetic diversity in cultivars
what happened in 1960s and 2006?
1960s - green revolution - high yielding crop varieties introduced
2006 - rice genome published
what does applied selection do?
improve yield
improve resource efficiency
increase disease resistance
operate on phenotypic traits - heritable changes
what does artificial selection do?
selection can’t distinguish between hetero/homo
selection for recessive alleles - favoured alleles fixed in single gen
selection for dom allele - selection less efficient as allele approaches fixation
what works better than artificial selection?
genetic markers
what is the infinitisimal polygenic model?
quantitative traits are assumed to be under the control of an infinite number of gene, each contributing small effect on phenotype - random sampling gives a normal distributed phenotype
what is phenotypic variance?
the sum of all genetic and environmental variance
what are the genotype effects?
they’re defined relative to their mid point
the genotypic value is composed of;
A - additive effects - sum of the effects of individual alleles
D - dominance effects - interactions between alleles at a single locus
I - epistatic effects - interactions between genes at two or more loci
what is genotypic variation?
Vg = Va + Vd + Vi
Va is the variation caused by additive effects passed from parent to offspring
the others are the dominance/interaction effects that are specific to individuals
what does narrow sense heritibility tell us?
the relative contribution of genetic effects that can be passed from parent to offspring
the proportion of phenotypic variance caused by additive genetic variance
what is the selection differential (S)?
the difference between mean of base pop and the mean of selected individuals
when does S increase?
when selection intensity increases
what is the response to selection?
a change in the mean phenotype of offspring of pop
what does response to selection depend on?
S and narrow sense heritability
the intensity of selection and contribution of additive and enviro effects
what happens if trait heritability is low?
breeding progress is low
why are crop genomes hard to sequence?
large genome size and repetitive
why are single genome sequences bad?
tell us nothing about genetic variation
what do reference genomes do?
allow cost effective genome wide resequencing across multiple individuals
what are SNPs?
single nucleotide polymorphisms
they are used to generate large numbers of genetic markers
what are QTLs?
markers linked to quantitative traits can be substituted for phenotypic selection
many influenced by single genes of large effect
predict quantitative phenotypes after new route to genetic gain
how does QTL mapping work?
make a cross between contrasting phenotypes
cross within F1 to get segregating F2 pops
genotype with genome-wide genetic markers
genetic markers tested for association with traits of interest
how does QTL mapping work in disease resistant barley?
resistant crossed with susceptible segregated F2 pop produced genotyped at 348 SNP loci field trials for disease resistance markers tested for association with disease
how does marker assisted selection work?
crosses made between contrasting parents
segregating pop genotyped for linked marker
initial selection based on marker genotypes
selected individuals taken forward for phenotypic investment
advantages of MAS
quick - seedling level, reduced gen time so faster genetic gain
cheap
response to selection doesn’t depend on environmental variation - effective when trait heritability low
