Traditional (historical) BreedingGradual (but dramatic) genetic change over long time periods through observation and selective

breeding (Instinctive Selection)

Modern BreedingEconomic 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? Breeding Goal

How to get there? Quantitative Genetics

Getting There Implementation

Selection TheoryGenetic EvaluationCrossing TheoryReproductive Technology

Tools

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 60 Goat 60 Sheep 54 Pig 38 Horse 64 Donkey 62 Mule 63

Chromosomes- Chromatin and DNA

DNA – Genetic Code for Protein SynthesisDNA – Polymer of Nucleotide Bases Nucleotide Sequence –Amino acid Sequence of the Protein (Shape and function)

I - DNA is the Genetic Code for Protein SynthesisProteins 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

gametes

B/b

B/ /b

1/2 1/2

Law of Independent Assortment

• Segregation of alleles at one locus is independent of segregation at other loci.

Bb Pp

BP

Bp

bP

bp

Black, polledparent

gametes

Terminology

• Dominant versus recessiveblack (B_) dominant to red (bb)

• Homozygous versus heterozygousBB or bb versus Bb

• SummaryBB = homozygous dominantBb = heterozygousbb = 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

• Size - frame• grazing area vs frame• market size vs frame• nutrition vs frame

Genetic/Repro Problems in Cattle

• 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