Traditional (historical) Breeding
Gradual (but dramatic) genetic change over long
time periods through observation and selective
breeding (Instinctive Selection)
Modern Breeding
Economic pressures for rapid genetic change
over short periods via optimal utilization of
available breeding tools
Co-improvement of
technologies on nutrition,
management
crossbreeding and genetic
improvement
What Animal Breeding is?
Where to go?
How to get there?
Breeding Goal
Quantitative Genetics
Selection
Tools
Getting There
Theory
Genetic Evaluation
Crossing Theory
Reproductive Technology
Implementation
What tools are available?
• Visual assessment
What tools are available?
• Visual assessment
• Pedigree Information
What tools are available?
• Visual assessment
• Pedigree Information
• Performance information
- simple, traditional measures
Ex: growth, fertility, calving easy
What tools are available?
• Visual assessment
• Pedigree Information
• Performance information
- simple, traditional measures
Ex: growth, fertility, calving easy
-Advanced measures
Ex: Ultrasound (IMF%, RE area, feed intake)
Basic Genetics and Cytogenetics
• Inheritance: May be defined as a tendency of parents
to generate offspring with similar characteristics.
• Variation: May be defined as every environmental or
germinal differences between organisms related by
ascendance. It can be due differences on the
environment (nongenetic) or on the genotypes
(genetic)
Some Definitions
• Gene: The basic unit of heredity consisting of a DNA
sequence at a specific location on a chromosome
• DNA: Deoxyribonucleic acid, the molecule that forms
the genetic code
• Chromosome: One of a number of long strands of DNA
and associated proteins present in the nucleus of every
cell
• Homolog: One of a pair of chromosome having
corresponding loci
• Locus: The specific location of a gene on a chromosome
• Allele: An alternative form of a gene
• Multiple alleles: More than two possible alleles at a
locus
Some Definitions
• Genotype: The combination of genes at a single locus
or at a number of loci*
• Homozygote: A one-locus genotype containing
functionally identical genes
• Heterozygote: A one-locus genotype containing
functionally different genes
• Segregation: The separation of the homolog
chromosome during meiosis
• Germ Cell or Gamete: A sex cell – a spermatozoid
(sperm) or ovule (egg)
• Meiosis: The process of germ cell formation
• Mitosis: The process of cell multiplication:
• Embryo: An organism I the early stages of development
in the shell (birds) or uterus (mammal)
Cells are classified into two types
1. Gametes (sex cells)
– sperm cell
– ovum or egg
• 1n chromosome
number at maturity
2. Somatic cells (non-sex
cells)
• 2n chromosome
number at maturity
Chromosomes
• Located in nucleus of cell.
• Each is a huge molecule, consisting of DNA and
proteins called histones.
• Occur in pairs in somatic cells, but as singles in
gametes. E.g., in humans:
– Somatic cells have 46 chromosomes (23 pairs).
– Gametes have 23 chromosomes.
– 2n = 46, 1n = 23
• The two chromosomes of a given pair are said to be
homologous to one another.
Chromosomes
• X and Y are known as sex chromosomes; others as
autosomes.
• Female:
– somatic cell contains X X
– ovum contains X
• Male:
– somatic cell contains XY
– sperm contains X or Y
• Genes determining gender are located on the sex
chromosomes
Chromosome Number for Selected
Species (2n)
Cattle
Goat
Sheep
Pig
Horse
Donkey
Mule
60
60
54
38
64
62
63
Chromosomes- Chromatin and
DNA
DNA – Genetic Code for Protein Synthesis
DNA – Polymer of Nucleotide Bases
Nucleotide Sequence –Amino acid
Sequence of the Protein (Shape and
function)
I - DNA is the Genetic Code for Protein Synthesis
Proteins can be Enzymes, Hormones, Transcription Factors,
Structural, etc.
Nucleotide Sequence –Amino acid Sequence of the Protein
Shape Determine the function/effect)
Genetic
Code for
Protein
Synthesis
DNA Replication Complementary
Bases
What are alleles?
• Alternative gene forms that occupy the same locus
on homologous chromosomes.
• e.g., black (B) / red (b) coat color gene in cattle
B
___._____________
___._____________
b
• Can have at most 2 alleles in an individual, but
more than 2 in a population (A/B/O blood-type).
Law of random segregation
– a random sample half of each gene pair of an
individual is transmitted to a gamete (and
offspring)
parent
B/b
1/2
1/2
B/
/b
gametes
Law of Independent Assortment
• Segregation of alleles at one locus is
independent of segregation at other loci.
Black, polled
B
P
Bb
B
p
Pp
b
P
parent
b
p
gametes
Terminology
• Dominant versus recessive
black (B_) dominant to red (bb)
• Homozygous versus heterozygous
BB or bb versus Bb
• Summary
BB = homozygous dominant
Bb = heterozygous
bb = homozygous recessive
Genetics =
Heredity X Environment
• Heredity: transmission of genetic or physical
traits of parents to their offspring.
• Environment: the sum total of all external
conditions which effect the life of the animal
Terminology
• Heritability: describes what fraction of the
differences in a trait is due to differences in
genetic value rather than environmental
factors.
• Hereditary variation: variation caused by the
heredity.
• Environmental variation: variation caused by
the environment.
Heritability Estimate
• Heritability estimate: hereditary variation due
to additive gene action.
• effects the rate of improvement
– low heritability lends to slow rates of
improvement
– high heritability estimates yields faster rates of
improvement
Economic Important Traits
•
•
•
•
•
•
•
•
•
205 day adjusted weaning weight
Yearling weight
Birth weight
Rib eye area
Intramuscular fat
Milk production
Average daily gain
Feed efficiency
Calf crop %
Heritability Estimates for economical
important traits
• Rate of Gain (feedlot cattle)
– 40-68%
• Ribeye Area
– 50-70%
• Calving Interval
(Fertility)
– 10 %
• Weaning Weight
– 30 %
• Birth Weight
– 40 %
• Fat Thickness
– 45 %
• Pasture Gain
– 30 %
• Cancer-eye Suscept.
– 30 %
Terminology
• Prepotency: the amount that an offspring
looks like the parent.
• Nicking: when genes of the dam and sire
complement each other.
• Heterosis: the improvement that the offspring
has over its parents.
Production Testing and Selection
• Performance testing- testing of the individual
• Progeny testing- testing of the offspring
• Pedigree selection- using the reputation or
records of animals for breeding selection
Multiple Trait Selection Systems
• Tandem- looking at intensifying on one trait at a time
• Independent Culling- using minimal criteria to select
for two or more economic important traits
• Selection Index- using the combination of two or
more economic important traits by observing an
index to make selections for breeding
Selection Differential, Estimated Breeding
Value and Expected Progeny Differences
• Definition of S.D.= the difference between
animals selected to be parents and the
average of all animals in the herd for
selection for a specific trait
• EBV = ave. of animals selected minus the
ave. of all animals X heritability
• EPD = EBV X .5
Expected Progeny Differences
• Definition – the expected performance of an
individual’s offspring relative to the average
individual of the entire breed.
• Examples – birth weight, weaning weight,
yearling weight, scrotal circumference, ribeye
area, etc.
• Understanding a Sire Summary
Types of Breeding
• Purebreeding systems:
– Outcrossing: the mating of relatively unrelated
animals within the same breed.
– Inbreeding: production of offspring from parents
more closely related than the average of a
population
– Line breeding: a form of inbreeding in which an
attempt is made to concentrate the inheritance of
some ancestor in the pedigree.
Crossbreeding Systems
– Crossbreeding: the mating of animals of different
breeds.
– two-breed cross
– two-breed backcross
– three-breed rotational cross
– three-breed terminal cross
Frame size vs. production vs. type
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•
•
•
Size - frame
grazing area vs frame
market size vs frame
nutrition vs frame
Genetic/Repro Problems in Cattle
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•
•
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Freemartins-hormonal influence
Dwarfism – genetic influence
Dark cutters / more environment
muscular hypertrophy (double muscling)
– increase in size of muscle fibers
– Quality vs quantity vs performance
Genetic Defects
• Tibial hemimelia (TH)
• Pulmonary Hypoplasia with Anasarca (PHA)
• Bovine Arthrogyrposis Multiplex Congenita (AM) aka curly
calf
• Neuropathic Hydrocephalus (NH)
• Dwarfism (Angus mutation, DW1)
• Osteopetrosis (OS) aka marble bone
• Contractual Arachnodactyly (CA)- aka Fawn Calf Syndrome