Livestock Genetics Ms. Boyt

How can genetics help us in the livestock industry? Selection- the breeding or mating of animals to produce certain desired traits or characteristics Characteristics bred for: o Horned or polled livestockLarge litter size o TemperamentMarbling o Low birth weight Heavy weaning weight o Milk productionColor

Today we will… Describe how individuals acquire their genes and where genes are located in the body. Define and distinguish between dominant and recessive traits. Define and distinguish between heterozygous and homozygous individuals. Define and distinguish between genotypes and phenotypes. Calculate genotypic and phenotypic ratios and outcomes.

Genetics The scientific study of the principles of heredity and the variation of inherited traits among related organisms

Where are these inherited traits found? Each of our cells contains a complete set of our genetic material in its nucleus. This genetic material is located in our chromosomes. Chromosomes are composed of long strands of DNA. Segments of DNA are called genes. Genes are the most basic unit of heredity.

Genes Segments of DNA Genes code for traits o Ex. Coat color, horns, size of ears Genes come in pairs (2 for every trait) One gene in the pair is called an allele Alleles of a gene are not created equally o They are either dominant or recessive

How do we know this? Gregor Johann Mendel Known as the “Father of Genetics” Lived Austrian Monk Studied the inheritance of traits in pea plants Developed the laws of inheritance

Gregor Johann Mendel Between 1856 and 1863 Mendel cultivated and tested around 28,000 pea plants He found that the pea plants offspring retained traits of the parent plants He used pea plants for many reasons o Inexpensive o Grow quickly o Normally self pollinate o Easy to cross pollinate o Produce many offspring

How did he do it? 1. He began by identifying pea plant traits

How did he do it? 2. He then produced pure(true breeding) strains by allowing plants with known traits to self pollinate for many generations. 3. Cross pollinated the pure breed of round seed plants with the pure breed of wrinkle seed plants.

How did he do it? 4.The next season Mendel planted 253 F1 (first generation) plants. F1 x F1= F2 7,324 total sees 5,474 were round (3/4) 1,850 were wrinkled (1/4)

How did he do it? Mendel repeated this experiment for the other known pea plant traits and in each case a 3:1 ratio occurred. Discovered that some traits were dominant to others Dominant- a trait (allele) that expresses itself over another o Ex: Round seeds Recessive- a trait (allele) that is masked by the dominant trait (allele) and does not show through in the first generation o Ex: Wrinkled seeds

Terminology Homozygous- contains two alleles that are the same o RR or rr Heterozygous- contains two different alleles o Rr Genotype- the internal genetic code individuals possess Phenotype- the outward physical appearance “Genotype codes for Phenotype”

Mendel’s Laws 1. Law of Dominance 2. Law of Segregation 3. Law of Independent Assortment

Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. o The trait that is observed in the offspring is dominant o The trait that disappears in the offspring is recessive Parent Pea PlantsF1 Pea Plants Tall stem x short stemAll tall stems Yellow seed x green seedAll yellow seeds Green pea pods x yellow pea podsAll green pea pods Round seeds x wrinkle seedsAll wrinkle seeds Axial flowers x terminal flowerAll axial flowers

Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. o Only receive one allele from each parent

Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. Ex: Seed color does not determine seed shape o Just because a seed is green does not mean it will be wrinkled and vise versa

Working with genetic traits We can illustrate traits by assigning them letters The dominant trait usually provides the designating letter The dominant trait is represented by a CAPITOL letter and the recessive trait is represented by a lower case letter o Ex. Round (R) vs Wrinkled (r) Traits are usually represented by two letters o One for each allele

Punnett Square A way of visualizing crosses and calculating outcomes of crosses Named for Reginald C. Punnett

Punnett Square Examples

Now you try!

Tell me what you know… Where are genes located in the body? What is the difference in genotypes and phenotypes? Define heterozygous and homozygous. What is the difference between dominant and recessive traits? What are punnett squares used for? How can genetics help us in the livestock industry?

Today we… Described how individuals acquire their genes and where genes are located in the body. Defined and distinguished between dominant and recessive traits. Defined and distinguished between heterozygous and homozygous individuals. Defined and distinguished between genotypes and phenotypes. Calculated genotypic and phenotypic ratios and outcomes.