Animals today are more productive
than the same animals 100 years ago.
How is this possible?
Part of this change comes from the
environment in which the animals
are raised being better now than they
were then.
More of this change comes from genetic
selection made by farmers over the years.
What exactly is genetics?
The study of heredity
Heredity- The way in which traits of
parents are passed on to offspring.
So genetics is...
The study of how traits are passed from parents to offspring.
The History of Genetics
Gregor Johann Mendel
- Considered to be the father of genetics
- Experimented mostly on garden peas
- Proved that certain characteristics like color and height are passed from parent to offspring.
Selection Based on Genetics
- Genotype vs. Phenotype
- Genotype
- Animals Genetic Makeup
- Phenotype
- Animals Physical Appearance
Can two animals have identical genotypes, but have different phenotypes? Why/Why not?
Yes they can.
Part of the animals phenotype comes from the environment the animal is born and raised in.
Additive and Nonadditive Gene Effects
Additive Gene Effects
- When many different genes are involved in the expression of a trait
- Individual genes have little or no effect on a trait
- Most traits that are economically important in the livestock industry are based on additive gene effects.
- Carcass traits, weight gain, milk production
Nonadditive gene effects
- Control traits by determining how gene pairs act in combination with each other
- Traits controlled by one or only a few pairs of genes
When a combination of gene pairs give good effects the offspring will be better than either of its parents.
This is called heterosis
Quantitative vs. Qualitative Traits
Quantitative Traits
- Traits that express themselves in a measurable way
- Carcass traits, weight gain, milk production
- Additive gene effects
Qualitative Traits
- Traits that express themselves in an immeasurable way
- Animals Phenotype
- Hair color, horns, eye color
- Nonadditive gene effects
Heritability
- The portion of the total variation (genetic and environmental) that is due to additive gene effects
- High heritability means that improvement in the characteristic will be quick
- Low heritability means improvement will be slow
There are 3 types of systems that are used when selecting breeding animals.
- Tandem
- Independent Culling Levels
- Selection Index
Tandem
- Selection for a single trait at a time
- Start selecting for a different trait when a desired level of production is reached in the first trait.
- Animals with some undesirable traits may be kept if they have the desirable trait.
- This is not the most profitable method of selection as its focus is too narrow.
- Least effective of selection methods.
Independent Culling Levels
- Sets a level for each trait that an animal must meet to be kept.
- Based on multiple traits.
- Doesn't take into account that some animals may be far superior in some traits as they may still be culled for being deficient in other traits.
- Most effective if there are a small number of traits that are being selected for.
- 2nd most effective method of selection overall.
Selection Index
- An index of averages that gives weights to different traits based on economic importance, heritability, and genetic correlation is used.
- Doesn't cull an animal for having only slightly substandard performance in one trait if that performance if offset by another traits superiority
- Provides a more rapid improvement in overall genetics.
- Extensive records are needed to establish an index like this.
- Most effective method of achieving improvement.
Mitosis
- Each animal begins as a single cell.
- This cell divides into 2 cells, and those each divide into 2 more and the cells just keep dividing to make the animal's body.
- This process in an animal is called mitosis.
Chromosomes occur in pairs in the animals body.
Each parent contributes one-half of each pair.
The number of pairs is called the diploid number and varies from species to species, but is constant for that species.
Genetics in the
Animal Industry
The Animal Cell
- An animals body is made up of millions of cells.
- Cells are the basic and smallest part of the body and are capable of sustaining life (metabolism and reproduction.
- The nucleus contains the hereditary material in chromosomes which hold the genes.
Diploid Numbers in Livestock
Cattle 30 Goat 30 Chicken 39
Swine 19 Horse 32 Rabbit 22
Sheep