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Exam 3 Genetics
Term | Definition |
---|---|
Backcrossing | mating of a hybrid to a purebred of a parent breed or line |
Repeated Backcrossing/Introgression | Mating system used to incorporate an allele(s) existing in one population into another population. An initial cross is followed by successive generations of backcrossing combined with selection for the desired allele(s) |
Grading Up/Topcrossing | To convert a population from one breed to another by mating to purebred sires |
Random Mating | -chose mate at random -occurs after selection - different from random selection |
Positive Assortative mating | mating of similar individuals -good at changing pop mean -dont use for intermediates |
Negative assortative mating | mating of dissimilar individuals -decreases variation -not good for changing pop -good uniformity for intermediates |
Assortative mating | -produces more variation -tends to produce extremes |
corrective mating | a type of negative assortative to correct parents faults in progeny |
Complementarity | type of corrective mating that results in breeding two complementary types to produce better offspring |
Maternal breed | a breed that excels in maternal traits of fertility, freedom from dystocia, milk production, mothering ability |
Paternal breed | breed that excels in paternal traits such as meat quality and carcass yield |
Terminal sire cross-breeding | system in which maternal-bred females are mated to paternal-breed sires to produce market offspring. All offspring are sold |
Inbreeding | mating of animals that are more closely related than the average of the population from which they came; increases homozygousity |
Prepotency | ability of an individual to produce offspring that resemble it; caused by inbreeding |
Inbreeding Depression | the expression of unfavorable recessive alleles influencing polygenic traits |
Hybrid vigor/heterosis | an increase in the performance of hybrids over that of purebreds, most noticeably in traits like fertility and survivability; increases GCV; may be (-) |
Inbreeding Coefficient (Fx) | the probability that both genes of a pair in an individual are identical by descent; measured for a pop at a particular time |
Wright's Coefficient of Relationship (Rxy) | the correlation between the BVs of 2 individuals due to pedigree relationship alone; |
Line breeding | mild form of inbreeding; |
Outbreeding | mating of individuals that are less related than the average pop; increases heterozygosity; can get HV |
Individual Hybrid Vigor | caused by the direct component(the effect of an individual's genes on its performance) of the trait |
Maternal Hybrid Vigor | the effect of the genes on the environment provided by the dam |
Paternal hybrid vigor | the effect of the genes on the environment provided by the sire |
retained hybrid vigor | hybrid vigor that remains in later generations of hybrids |
composite animal | a hybrid with at least two and typically more breeds in its background; expected to be bred to own kind |
composite breed | a breed made up of two or more component breeds and designed to benefit from hybrid vigor without crossing with other breeds |
composite system | a mating system limited to matings within a single composite breed |
spatial rotation | breeding systems in which generation of females are "rotated" among breed sires whose breed comp is most different from their own |
rotations in time | system in which sire breeds are not used simultaneously but are introduced in sequence |
terminal sire system | where maternal-breed females are mated to paternal-breed sires to produce progeny that are desirable to the market; does not create replacements |