Animal Science

The art and science of genetic improvement in farm animals

Animal Breeding

The basic biological unit of inheritance

Gene

Proposed the double-helix structure of DNA, building on Rosalind and Maurice Wilkins’s work.

James Watson & Francis Crick 1953

Known as the father of genetics, studies peas

Gregor Mendel 1866

Pioneered selective breeding in horses, sheep, and cattle, focusing on meat production and carcass quality.

Robert Bakewell 1870

First to demonstrate Mendelian inheritance in animals.

William Bateson 1902

Developed the Hardy-Weinberg theorem, explaining genetic equilibirum in populations.

Hardy & Weinberg 1908

Applied ANOVA to study genetic correlations among relatives.

Ronald Fisher 1918

Introduced mating systems and the path coefficient method in genetic studies

Sewall Wright 1921

Developed the selection index, a tool for genetic improvement in animal breeding

L.N Hazel 1943

Father of animal breeding and genetics, applied population genetics principles to enhance animal breeding strategies.

Jay Lush 1945

Used mathematical probability to analyze genetic relationships.

Malecot 1948

Coined the term gene and distinguished genotype from phenotype

Wilhelm Ludvig Johansen

What is DNA?

Deoxyribonucleic acid

threadlike structures in the cell nucleus that carry genetic information.

Chromosome

A Segment of DNA that determines the base sequence of nucleotides in messenger RNA.

Gene

What is RNA

ribonucleic acid

Chromosome responsible for sex determination, represnted by X and Y.

Sex chromosomes

The observable characteristics of an individual

Phenotype

Formula of Phenotype

P = G + E + ( G x E )

The genetic makeup of an individual, determining inherited traits.

Genotype

The way genes influence traits

Gene action

Combined effect of multiple genes contriutes a trait.

Additive

one allele masks the expression of another.

Dominance

One gene influences the expression of another gene.

Epistasis

Non-genetic factors that influence phenotype, such as nutrient, physical environment and management

Environment

Certain genotypes perform better in specific environments compared to others.

Genotype X Environment interaction

The improved size, growth rate, fertility, and yield of hybrid organisms compared to their parents.

Heterosis

traits with low heritability respond slowly to selection because their variation is largely influenced by environmental factors rather than genetics.

Heritability and selection response

Crossbreeding can enhance traits with low heritability by maximizing genetic diversity and hybrid vigor.

Heterosis and lowly heritable traits.

The way alleles interact to influence phenotype

Forms of Dominance

Both alleles are expressed

Lack of Dominance

One allele is not completely dominant, leading to an intermediate phenotype.

Partial Dominance

The heterozygote has a superior advantage over either homozygote.

Overdominance

The process of producing reproductive cells

Gametogenesis

Occurs in males, producing sperm cells

Spermatogenesis

Occurs in females, producing egg cells.

Oogenesis

The fusion of sperm and egg to form a zygote or embryo.

Fertilization

produces genetically identical diploid (2n) cells for growth, repair, and asexual reproduction (e.g., skin, muscle, liver, and blood cells).

Mitosis

generates haploid 👎 gametes, promoting genetic diversity through crossing over and independent assortment (e.g., sperm and egg cells from testes and ovaries).

Meiosis

A single nucleotide is altered

Point Mutation

Extra nucleotide bases are added, potentially disrupting gene function

Insertion

A section of DNA is removed, possibly leading to loss of function.

Deletion

A gene segment is copied, sometimes leading to enhanced traits.

Duplication

A segment of a chromosome flips and reattaches, altering gene expression.

Inversion

A chromosome segment moves to a different chromosome, causing genetic shifts

Translocation

Each parent passes only one allele for a given trait to their offspring. Example: A cow with black fur and a cow with white fur will produce offspring with either black or white fur, not a mix.

Law of Segregation

Different traits are inherited separately from each other. Example: A farm animal's fur color does not determine its horn shape.

Law of Independent Assortment

A dominant allele will always be expressed over a recessive one. Example: If a chicken carries a dominant feather pattern trait, it will be expressed even if a recessive version is present.

Law of Dominance

Genes located close together on the same chromosome tend to be inherited together.

Linkage

Crossing over during meiosis can break gene linkage, leading to genetic diversity.

Recombination

Traits are carried on sex chromosomes (X and Y).

Sex-Linked Inheritance

Gene Pool

The total set of genes available in a population for inheritance, shaping future traits.

Occurs when a single gene affects two or more seemingly unrelated traits.

Pleiotropy

A group of animals sharing a gene pool, with genetic variation influencing breeding outcomes.

Population

The proportion of different gene variants (alleles) in a population determines how common a trait is.

Gene Frequencies

inhertiance occurs when a trait is controlled by several genes, each contributing a small additive effect to the overall phenotype

polygenic

Gene frequencies remain stable if no selection, mutation, or migration occurs.

Hardy-Weinberg Equilibrium

Farmers breed animals with desirable traits, increasing their frequency over generations.

Selection

In small herds or flocks, random changes in gene frequencies occur due to chance

Genetic Drift

Spontaneous gene changes introduce new traits, which can be inherited if they affect reproductive cells.

Mutation

Introducing new animals into a herd or flock brings fresh genetic material, influencing diversity. Mating Strategies and Their Effects

Migration

Mating choices are influenced by specific traits rather than being completely random.

Non-random mating

Similar animals mate, increasing uniformity and homozygosity.

Assortative mating

Different-looking animals mate, promoting genetic diversity.

Disassortative Mating

Mating of closely related animals, increasing homozygosity but also the risk of genetic disorders.

inbreeding.

Refers to the physical differences between males and females of the same species beyond their reproductive organs.

Sexual dimorphisms

pros of inbreeding

Produces consistent traits, strengthens desirable genes (e.g., high milk yield in dairy cattle).

cons of inbreeding

Reduces fertility, growth rate, and vigor; increases genetic disorders (inbreeding depression).

Very close relatives (e.g., brother-sister, sire-daughter).

Close breeding

Less related animals (e.g., half-siblings, cousins) to preserve elite bloodlines.

Line breeding

Mating animals from different breeds to improve performance through Hybrid Vigor (Heterosis)

crossbreeding

2 breeds breeding

single cross

Crossbred x third breed, breeding

three-way cross

2 single crosses mated

four way cross

Alternate backcrossing with parent breeds

Crisscrossing

Repeated crossing to a common ancestor

backcrossing

It involves stimulating a superior donor cow to produce multiple eggs, artificially inseminating her, collecting and evaluating the fertilized embryos, and transferring them into synchronized recipient cows to carry the pregnancies

Multiple Ovulation and Embryo Transfer (MOET)

Inducing the donor cow to release multiple eggs.

Superovulation

Aligning the reproductive cycles of donor and recipient cows.

Estrus Synchronization

Using semen from superior bulls instead of natural mating.

Artificial Insemination (Al)

Collecting embryos from the donor cow's uterus.

Flushing

Implanting embryos into recipient cows.

Embryo Transfer (ET)

Freezing embryos for future use

Cryopreservation

A subdivision within a breed, differing in color or feather pattern

Variety

A genetically distinct line within a breed, selectively bred for specific traits

Strain

A group of birds with shared physical traits and genetic uniformity, recognized by poultry organizations

Breed

Classification based on purpose, such as meat-type (broilers) or egg-type (layers).

Type

A protrusion of internal organs due to weak body walls, commonly seen as scrotal or umbilical hernias in pigs and cattle.

Hernia

A condition where only one testicle descends, potentially reducing fertility in pigs, cattle, and horses.

Monorchidism

One or both testicles fail to descend, affecting fertility (common in pigs and cattle)

Cryptorchidism

Difficult birth due to large fetus size, poor positioning, or maternal factors, often requiring veterinary assistance.

Dystocia

A dead fetus is retained in the uterus, dehydrating and shrinking instead of being expelled, common in pigs and cattle.

Mummification

Failure of females to show heat cycles, leading to infertility (common in cattle).

Anestrus

Female ovulates but does not show visible signs of estrus, making detection difficult (seen in dairy cows and goats).

Silent Heat

Calcium deficiency in high-producing dairy cows post-calving, leading to weakness or paralysis.

Milk Fever (Hypocalcemia)

Selection based solely on individual merit or performance (phenotypic selection).

Individual Selection

Selection based on the performance records of immediate relatives

Pedigree Selection

Selection based on sibling performance, excluding individual records.

Sib Selection

Based on half-sibling performance (same sire or dam).

Half-Sib (HS)