Lecture 14 - Selecting Flashcards
what should you consider when selecting for qualitative traits
-big differences in the phenotype
-little environmental effect
-high heritability
-early and generally anywhere
what you should consider when selecting for quantitative traits
- small differences between phenotypes
-large environmental effects and lower heritability
-should select for in home location
in inbreeding species, the lower the heritability, the _______ generations of selfing you should go through before selecting
more
what would selecting on dominant gene action mean for the response to selection
it will go down because of hidden heterozygotes
steps to plant breeding
-set objectives
-gather genetic variation
-selection (response to selection and breeding methods)
-trials
-registration and commercialization
process for getting from segregating population to cultivar depends on…
-crop type
-objectives
-heritability of trait of interest
-size of breeding program
-time frame
-personal preference of the breeder
mass selection
a breeding procedure in which seed from phenotypically desirable individuals is bulked and planted to produce the next generation
what is selection in mass selection based on
-phenotypic appearance of individual plants
-progeny rows of individual plants
objective of mass selection
increase the frequency of superior genotypes in the population
t/f: mass selection is an expensive form of population improvement
f, it is the simplest and cheapest form of pop improvement
what type of crossing species can mass selection be used for
self pollinated or out-crossing (out-crossing more popular)
advantages of mass selection
-simple, inexpensive
-large populations can be handled with ease
-population more flexible than a pure line
disadvantages of mass selection
-selection based on phenotype
-sensitive to environment
-non-uniform product
when would mass selection be used
-population improvement
-maintain breeder seed
-inexpensive way to improve mainstream breeding populations
-loosely done in early generations of all breeding methods
why is mass selection more often used in outcrossing crops
outcrossing crops are populations anyways, so they have a lot of heterozygosity
breeding methods of inbreeding crops
pure line selection
development of inbred lines
goal of breeding inbreeding crops
homozygous, reasonably homogeneous population
pure-line selection
modified mass selection for inbreeding species that produces a population composed of progeny of a single superior genotype that is homogeneous
why does selection for moderate to highly heritable traits occur among lines in pure-line selection
because variation within a row is likely due to environment, variation between rows is more likely genetic
steps of pure-line selection
- visually select single plants in a homozygous line population for highly heritable traits
-grow in progeny rows and select lines
-replicate for yield trials
when would you use pure-line selection
-to generate adapted parental material for new program
-species with little breeding effort
-species introduced to a new area
development of inbred lines
creating variability through the crossing of diverse parents
_____ generation is the critical generation for selection in development of inbred lines. Why?
F2. It has the max variability to choose from (if big population), so failing to chose the best will result in its loss forever
how does the distribution of alleles among parents change depending on the cross
in a cross AABB x aabb, the variation of the F2 is the range of the parent expression
in the cross AAbb x aaBB, the variation of F2 can exceed that observed in the parents (transgressive segregation)
transgressive segregation
the limit of variation in the F2 can exceed that observed in the parents
