ANS 309 - ANIMAL BREEDING

System

a group of interdependent component parts

ex: family, poultry

How do we improve livestock?

1. environment - non-genetic

2. nutrition health

3. facilities

4. stockmanship/animal handling

5. genetics

Interaction

a relationship among components of a system in which the effect of one component depends on the other components present in the system

Intermediate Optimum

An intermediate level of performance that is optimal in terms of profitability and/or function

Trait

Any measurable or observable characteristic of an individual

Examples of observable or measurable characteristic

swine muscling

shell-hardness-thickness

Qualitative Traits

• categorical

• controlled by 1 or few genes (simply-inherited)

• not affected by environment

Quantitative Traits

• numeric (continuous distribution)

• controlled by many genes (polygenic)

• changed/affected by environment

Phenotype

An observed category or measured level of performance for a trait in an individual

Genotype

genetic makeup of an individual

Environmental Effects

the effect of external (nongenetic) factors on animal performance

How do we define or describe genotypes?

1. all the genes & gene combo in general that affect an array of traits

2. specific genes & gene combos that affect a specific trait

3. genetic sequence at a particular locus

Biological Type

classification for animals with similar genotypes for traits of interest

ex: prolific wool sheep

How do we genetically improve livestock?

Trying to increase the prevalence or frequency of

1. favorable genes or individual gene lvl

2. gene combinations

improving or changing individuals/herd averages

Population

a group of intermating individuals

ex: breed, herd, entire species

Selection

the process that determines which individuals become parents, how many offspring they produce, and how long they remain in the population

Natural Selection

selection that occurs in nature independent of deliberate human control

Artificial Selection

selection that is under human control

Replacement selection

process that determines which individuals become parents for the first time

Culling

process that determines which parents will no longer remain parents

Breeding Value

The value of an individual as a (genetic) parent

What are the advantages of phenotypic selection?

1. easy-straightforward

2. adequate for some traits

What are the disadvantages of phenotypic selection?

1. genotype (genetics) is masked by environment

Phenotypic Selection

Selection based solely on an individuals own phenotype(s)

Heritability

a measure of the strength of the relationship between breeding values and phenotypic values for a trait in a population

High heritability

phenotypes are a good indicator of underlying breeding values and phenotypic selection is effective

Low heritability

phenotype is not a good indicator and phenotypic selection is ineffective

Performance Testing

Systematic measurement of performance (phenotype) in a population

Pedigree Data

Information on the genotypes and/or performance of ancestors or collateral relatives including

Collateral Relatives

relatives that a neither direct ancestors or descendants of an individual

2 benefits of using relative info

1. sometimes relatives are the only source of info

2. increases accuracy

Accuracy

a measure of the strength of the relationship between true value and their predictions or estimation

Accuracy is a function of…

1. heritability

2. amount of data/observations

3. type of data observations - pedigree data, individual data, and progeny

Progeny Data

information on the genotype of performance of descendants of an individual

considered “best” source

Genetic Prediction

the area of academic animal breeding concerned with measurement of data, statistical procedures, and computational techniques for predicting breeding values and related values

Mating

The process that determines which selected males or bred to which selected females

Mating System

a set of rules for mating

3 Strategies of Mating Systems

1. Produce extremes or increase the rate of genetic change

2. Complementarity = an improvement in the overall performance of offspring resulting from mating individuals with different but complementarity breeding values

3. Hybrid Vigor or Heterosis = an increase in the performance of hybrids over that of the purebreds

Crossbreeding

The mating of sires of one breed or breed combination to dams of another breed or breed combination

Hybrid

an individual that is a combo of

species

breeds (crossbred)

lines

Inbreeding

the mating of relatives

Inbreeding Cons

The appearance or increase in expression of genetic defects

• Inbreeding Depression = reverse of hybrid vigor – decrease in performance of inbred individuals

Inbreeding Pros

Create breeds or lines that when crossed produce hybrid vigor

• Concentrate a genotype that excels in specific area or trait

• Increase uniformity or homozygosity

Corrective Mating

a mating designed to correct in their progeny faults of one or both parents

Mendelian Genetics

study of transmission of traits from generation to generation

Molecular Genetics

How genetic information is encoded within DNA and how

biochemical processes of cell translate the genetic information into

phenotype

Population Genetics

Study of genetic variation between and within populations

study of factors affecting gene & genotypic frequencies in a population

Gene

basic physical 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 (macromolecule)

Chromosome

One of a number of long strands of DNA

and associated proteins present in the nucleus of every

cell

Homologs

One pair of chromosomes

having corresponding loci

Locus

specific location of a gene on a

chromosome

Allele

An alternative form of a gene

Multiple Alleles

more than 2 possible alleles at

a locus

Homozygous Dominant

2 copies of dominant allele

Homozygous Recessive

2 copies of recessive allele

Heterozygous

1 copy of each of a dominant and recessive allel

Haploid

only 1 copy of a gene

Homozygous Genotype (Homozygote)

A genotype

containing functionally identical genes

Heterozygous Genotype (Heterozygote)

A genotype

containing functionally different genes

Law of Segregation (and Recombination)

The

separation of paired genes during germ cell formation

Meiosis

process of germ cell (gamete) formation

At fertilization gene combinations are either

1. restored

2. created

Law of Independent Assortment

the independent

segregation (separation) of genes at different loci

Linkage

the occurrence that two or more loci of interest are on the same chromosome

Crossing Over

a reciprocal exchange of chromosome segments between homologs (during meiosis)

Recombination

The formation of a new combination of genes on a chromosome as a result of crossing over

Dominance

the interaction of genes at a single locus

such that in heterozygotes on allele has more effect than

the other. The allele with the greatest effect is dominant

over it’s recessive counterpart

Complete Dominance

A form of dominance in which the expression of the

heterozygote is identical to the expression of homozygous

dominant genotype

Co-Dominance/No Dominance

Both alleles are expressed and can be observed

Partial Dominance

Expression of heterozygote more

closely resembles the expression of either homozygous

genotypes

Overdominance

A form of dominance in which the expression of the

heterozygote is outside the range of expression defined

by the homozygous genotypes and most closely

resembles the expression of the homozygous dominant

genotype

Epistasis

An interaction among genes at different loci

such that the expression of genes at one locus

depends on the alleles present at one or more

other loci

Sex-Limited

Expression limited to one sex

Sex-Influenced

modes of gene expression change between male and female

Sex-Related Inheritance

Expression differences in males and females

True Breeding Lines

parental lines reproduce offspring with all the same characteristics as themselves

1. true-breeding - flower, wildlife

2. parental - biology/ans

3. purebred

Cross Pollination

1. true breeding x true breeding = F1 GEN

2. parental x parental = progeny F1

What did Mendel observe or learn from the outcomes

100% of same phenotype

Mendel’s Law of Inheritance

1. Particles (factors) (genes) can exist in different forms

2. The yellow (or green) was present in the F₁ progeny. So, there must be 2 copies

3. Genes interact! That one form has the ability to mask/hide the other or one dominates the other

What if you took the offspring from the black and red cross (F1’s) and mated them to each other?

75% black

25% red

Central Dogma

Genetic Code —→ DNA (transcription) —→ mRNA (translation) —→ protein —→ create other molecules like lipid/carbs

How lucky was Mendel?

1. 2 alles - 1 completely dominant to the other

2. 7 traits were on diff chromosomes

Zygote

a cell formed from the union of a male and female gamete

• diploid/2n

• one-celled embryo (1st stage)

Embryo

an organism in the early stages of development

Gamete Selection

determines which egg matures and which sperm fertilizes the egg

What are the # of possible gametes?

2n

What are the # of possible unique zygotes?

3ⁿ x 2^m

Sum or Addition Rule

The probability sum rule (or addition rule) calculates the probability

of one event OR another happening of two (or more) mutually

exclusive events occurring is the sum of their probabilitie

Product Rule

The probability product rule calculates the likelihood of two or more

events happening together

• The probability of one event AND another happening of two (or

more) mutually exclusive events

What are the processes of animal breeding?

1. process/selection - choosing individuals

2. mating systems

What are the outcomes of animal breeding?

1. frequency of favorable genes goes up

2. frequency of favorable gene combos go up

Outbreeding

mating of unreleated individuals

Parental Lines

original lines that start cross

Parental Cross

cross between true-breeding lines/pure lines and considering just 1 trait

produces: F1 gen, crossbred, & hybrids

6 types of crosses

1. AA x AA

2. aa x aa

3. AA x aa

4. AA x Aa

5. Aa x aa

6. Aa x Aa

Purelines/Purebred

only 1 outcome will breed true

Monohybrid cross/ F₁ x F₁

F2 or 2nd cross

Bb x Bb

Dihybrid Cross

BbPp x Bp

number of columns (sire) & rows (dam) of the square are determined by the # of possible genotypes

Reciprocal Cross

reverse parental lines by sex