Lecture 13

the ability of parents to combine amongst each other so that favorable genes/alleles are transmitted to their progenies

• the deviation in performance of hybrids from the expected productivity based upon the
• average performance of lines involved in the hybrid combination
•  Differences in SCA are attributed to
• non-additive genetic variation

• —the average performance of a line in a series of crosses
•  Evaluates the additive portion of
• genetic effects
•  Difference in GCA are due to additive
• and additive x additive interactions in
• the base population

•  The higher the GCA value, the better
• that parent will perform in a myriad of
• crosses
•  The higher the SCA, the better hybrid
• those lines will make
•  Used a lot in cross-pollinating species
• where hybrid vigor is desired

•  Population Genetics—change in the
• genetic structure of a population of plants
•  Change the gene frequency such that
• desirable genotypes predominate in the
• population
•  Cyclical selection (recurrent selection)
• increases the frequency of favorable
• genes

—selection is practiced within a specific population for its improvement for a specific purpose

—entails selection on the basis of the performance of a cross between two populations (used for hybrid production)

•  Goal-improve the performance of a population
• with respect to a trait such that the new
• population is superior in mean performance
•  Population is improved without the reduction in
• genetic variability
•  Population can respond to future improvements
•  Parents of the cross should be high performing
• regarding the traits of interest
•  Parents should not be closely related
•  More rounds of mating increases the
• opportunity for recombination

•  Individual families are created for evaluation
•  Parents are crossed in all possible combinations
•  The plants/families are evaluated and new
• parents selected
•  The selected parents are intermated to produce
• a new population for future selection

•  Used to better manage G x E interactions
•  Genetic gain is both inter and intra family
• selection
•  Often used with perennial species

•  Advantages
•  Suited for improving traits of high
• heritability
•  Good for plants with self-incompatibility or
• male sterile
•  Disadvantages
•  Based on maternal plant selection, so
• heritability estimates are reduced 50%
•  Less effective for low heritability traits

•  Advantages:
•  More precise evaluation of selected plant
•  Rapid to conduct
•  Disadvantages:
•  Must be able to self-pollinate
•  Need a lot of seed for subsequent progeny
• trials

•  Usually rapid to conduct
•  Increase frequency of desirable alleles
•  Progeny/test cross allows a more precise
• evaluation of the genotype of selected
• plants

• Disadvantages-Half-sib methods
•  In some cases, a lot of seed is needed for
• subsequent years testing
•  Trait should have high heritability
•  Some methods require self-pollination