Lecture 10 - Selecting Flashcards
what type of variance sets our breeding progress
genetic variance
what is the most meaningful type of genetic variance in breeding
additive variance (can be inherited to next cycle
response to selection is a function of ….
selection intensity, heritability, and phenotypic variance
selection intensity (i)
a function of the proportion of the total population selection selected (retaining 1% of pop is higher intensity than keeping 10%)
heritability (h2)
function of the amount of total variability due to genetic causes
_____ the heritability, the more complex and resource intensive selection will be
lower
phenotypic variabilty
a function of both genetic variation and environmental variation (want environmental as low as possible)
t/f: genetic variation is not a function of parental choice
f, it is
elite x elite = less genetic variation
elite x wild = more genetic variation
how to increase genetic gain
increase selection intensity
increase phenotypic variability
maximize heritability
how to increase selection intensity
- retain fewer genotypes
- test more genotypes but retain the same number
problems with increasing selection intensity
- potential genetic drift
- larger trials = increased error/environment (lower h2)
how to increase phenotypic variability
cross 2 or more genetically unrelated (diverse) parents to maximize genetic variance
problem with increasing phenotypic variability (breeders dilemma)
results in lower unselected population mean, which means more work is needed to meet objectives
best strategy to increase genetic gain
maximize heribitability
how to maximize heritability
replication
uniform nurseries
eliminating abiotic/biotic stresses
3 main strategies to improve more than 1 trait at the same time
tandem selection
independent culling
index selection
tandem selection
sequential selection for each trait, where each generation focuses on a different trait
limitation of tandem selection
- length of time required to improve all traits
- loss of genetic variation for traits selected at the end of the selection program (stops your ability to select0
independent culling/truncation selection
selection for each trait successively in the same generation, where only individuals that meet all parameters get to go to the next gen
limitations of independent culling
- population size is severely reduced in a single gen (selection intensity is high)
- lack of variation can be detrimental to a program
index selection
each genotype is assigned an index based on a weighted value assigned to each of the traits being selected to allow compromise
most breeders use the _________ selection
mental index
