Genetics 3
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Heritability
-the proportion of the phenotypic variation that can be passed from parent to offspring -can be used to predict the rate of genetic progress -values in the range 0-1
Low Heritablilty:
0-0.2 reproductive traits
Moderate heritability
0.3-0.4 growth rates
High Heritability
0.5-0.6 Carcass Traits
Selectional difference
Selected animal measurement-group average=selection differential
Generational Interval
-Average period of time between the birth of one and the birth of the next generation Gen interval= (average age of breeding females+average age of breeding males) /2
Generational Interval per species
Beef: ⅚ years Dairy:¾ years
Genetic progress dependent on
-heritability -selectional differential -generation interval-animals with shorter generation intervals will exhibit more rapid genetic progress
Population genetics: Hardy-Weinberg equilibrium
-gene and genotype frequencies remain constant in a population -does not occur in domesticated animal populations
Requirements’ for Hardy-Weinberg equilibrium
-large population -random mating -no migration -no mutations -no selection
Genetic Drift
-each generation will have a new frequency of alleles and genotype frequencies -2 special cases
Bottleneck
small population size for at least 1 generation created less genetic variation
Founder Effect
when a new colony is created from only a few members of a previous colony less genetic variation exists
Mutations
-mutation is simply a change in the DNA that can affect the expression of a gene -form abnormal proteins -reduce synthesis of proteins -change the rate of protein synthesis
Mutations are permanent changes due to
-DNA breakage -DNA loss -DNA rearrangement
Mutations in Germline cells:
These cells create gametes can be inherited
Mutations in Somatic cells
not inherited usually give rise to cancers and some congenital conditions
Causes of mutations
-environment -excessive UV light, radiation -errors during cell division
Cause of somatic cell mutations during cell division
mitosis
cause of germline cell mutations during cell divison
mesisos
Can mutations be fixed?
depends Cells contain dna repair proteins to proofread and fix mistakes in the dna
Point Mutation
-single nucleotide base is substituted by a different base
types of point mutations
silent missense nonsense
Silent point mutation
no effect on protien sequence