1. Breeding and Genetics 101

2. Understanding Breeds

3. Outline What's the “Best” animal Genes, Chromosomes and Genotypes
Traits, Genotypes, Phenotypes
Genes, Chromosomes and Genotypes
Dominance and Epistasis
Simply inherited vs. polygenic traits
Statistics and Their Role in Animal Breeding.
Variation, Heritability, Genetic Evaluation
Hybrid Vigor/Heterosis
The Genetic Model
Breeding Value, Producing Ability

4. Traits – Any observable or measurable characteristic of an animal.
What's the “Best”
Animals are usually characterized in terms of appearance or performance or a combination of both.
Traits – Any observable or measurable characteristic of an animal.
Coat color
Muscling
Weaning Weight
Marbling
Temperment

5. Traits do not describe an individual.
Traits and Phenotype
Traits do not describe an individual.
A red calf has weighted 576 lbs at weaning.
Phenotype – an observed category or level of performance for a trait.
Red and 576 are phenotypes for coat color and weaning wt

6. What Determines Phenotype?
P = G + E
Genotype – the genetic makeup of an animal
Environmental Effects – the effect of an external (non-genetic) factor has on phenotype

7. G x E Interaction

8. DNA – deoxyribonucleic acid
Genetics to Genes
DNA – deoxyribonucleic acid
Genetic code of 4 bases
Chromosome – a long strand of DNA, present in cell nucleus.
Cattle have 30 pairs
Humans have 23 pairs
Dogs have 39 pairs
Gene – the basic unit of inheritance.
Consists of DNA at a specific region on a chromosome
Allele – alternate forms of a gene

9. DNA

10. Heterozygous – having two different alleles for a particular locus
Hetrozygosity
Homozygous – posessing two copies of the same allele for a particular locus
Heterozygous – having two different alleles for a particular locus

11. Dominance
Dominant Allele - when present will override expression of any other allele for that trait
Recessive Allele – can only be expressed when both recessive copies of the allele are present for a particular trait

12. h H Hh Punnett Square Polled 100% Polled Homozygous Horned
Homozygous Polled
100% Polled

13. H h HH Hh hh Punnett Square Horned Polled 75% Polled
Heterozygous Polled
Hetrozygous Polled
75% Polled

14. H h HH Hh Punnett Square Horned Polled 50% Polled Heterozygous polled
Homozygous Horned
50% Polled

15. Gene Interaction
Epistasis – An interaction among different loci such that the expression of one gene depends on another

16. Epistasis Angus Charolais 100% Black Coat Partial Diluted = Grey Ed eD
EeDd
Charolais
100% Black Coat Partial Diluted = Grey

17. Epistasis A x C A x C ED eD Ed ed EEDD EeDD EEDd EeDd eeDD eeDd Eedd

18. Simple and Polygenic Traits
Simply inherited trait – a trait that is affected by only one gene
Polygentic trait – a trait affected by many genes, no single gene having an overriding influence

19. Variation – differences among individuals within a population
Statistics
Mean – the average
Variation – differences among individuals within a population
Variance is the measure of variation
Covariation is how two traits vary together

21. Variation and Covariation
Variation - Good or Bad?
Bad – adds to inconsistency
Good – Allows for increase selection efficiency
Measured as variance
Covariation – Good or Bad?
Good – allows for one trait to indicate another
Bad – negative trait may be coupled with a positive
Measured as covariance
Correlation is the square root of covariance

22. Breeding Value
Part of the animals genotypic value that is due to transmittable gene effects
The value of a parents genes to its progeny’s performance
Not all of the genotypic value is heritable
An EPD is ½ the expected breeding value (EBV)

23. Many ways to look at it: Heritability
The extent that the difference we observe in animal performance are due to inheritance.
A measure of the strength of the relationship between performance (phenotypic values) and breeding values for a trait.
It is a measure of correlation between breeding value and phenotype

24. Heritability Estimates
Trait h2
Calving interval
.05
Birth Weight
.40
Weaning Weight
.30
Mature Weight
Feed Conversion
Scrotal Circumference
.50
Backfat Thickness
Marbling Score
.35

25. Heritability and Selection
Heritability is critical to selection
The objective is to choose the animals with the best breeding values to become parents
To do this we need the best info available, in most cases phenotype is used
So the strength of relationship between phenotype and breeding values is very important

26. GCV = Gene Combination value
Genetic Model
Remember P = G + E?
Lets expand that to:
P = BV + GCV + E
GCV = Gene Combination value
Includes Epistatic effects and heterorsis

27. Heterosis
An increase in performance of hybrids over that of purebreds. Also caller Hybrid Vigor
Results in increased heterozygosity
Hereford 500 lb wwt average
Angus 500 lb wwt average
H x A 525 lb wwt average

28. More noticeable improvement in reproductive traits
Heterosis
More noticeable improvement in reproductive traits
Low heritability traits
Heterosis effects are not heritable, must be created every generation

29. The only heritable portion of this is BV
Genetic Model
P = BV + GCV + E
The only heritable portion of this is BV
All national cattle evaluation programs center on prediction of BV (EBV)

30. Questions