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Genetics of Animal Breeding

Genetics of Animal Breeding. Chapter 9. Objectives. Explain how genetics relates to improvement in livestock production Describe how cell division occurs Diagram and explain how animal characteristics are transmitted Diagram and explain sex determination, linkage, crossover, and mutation.

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Genetics of Animal Breeding

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  1. Genetics of Animal Breeding Chapter 9

  2. Objectives • Explain how genetics relates to improvement in livestock production • Describe how cell division occurs • Diagram and explain how animal characteristics are transmitted • Diagram and explain sex determination, linkage, crossover, and mutation

  3. The Importance of Genetics • Today’s farm animals are more efficient • Gregor Johann Mendel founder of genetics • Mendel proved that certain characteristics are passed from parent to offspring • Not all differences are caused by genetics • Some differences caused by environment

  4. Selection Based on Genetics • Additive and Nonadditive Gene Effects • Additive gene effects • Effect of many individual genes is cumulative • Control most livestock traits • Nonadditive gene effects • Controlled by only one of few pairs of genes • One gene in pair is typically dominant

  5. Selection Based on Genetics (cont.) • Heritability Estimates • Likelihood of a gene being passed on • Selecting Breeding Stock • Tandem • Independent culling levels • Selection index

  6. The Cell and Cell Division • Animal’s body comprised of millions of cells • Most cell material is protoplasm • Nucleus contains hereditary material, called chromosomes • Chromosomes contain genes • Nucleus controls cell’s metabolism, growth, and reproduction

  7. The Cell and Cell Division (cont.)

  8. The Cell and Cell Division (cont.) • Mitosis • Division of body cells in animals • Increases amount of body cells, causing growth • Chromosome pairs duplicated in each new cell • Four typical stages: prophase, metaphase, anaphase, and telophase

  9. The Cell and Cell Division (cont.) • Mitosis (cont.)

  10. The Cell and Cell Division (cont.) • Meiosis • Creates gametes (sperm or egg cells) • Chromosomes in gametes reduced by one-half • Chromosome pairs divided so each gamete has one of each type of chromosome • After fertilization, zygote will have one set of chromosomes from sperm, one from ovum

  11. The Cell and Cell Division (cont.) • Meiosis (cont.)

  12. The Cell and Cell Division (cont.) • Meiosis (cont.)

  13. The Cell and Cell Division (cont.) • Fertilization • Occurs when male sperm reaches female egg • Two haploid cells unite to form one complete cell, or zygote • Process results in many different possible combinations of traits in offspring

  14. Transmission of Characteristics • Genes • Characteristics are passed on by genes • Genes provide the code for protein and enzyme synthesis • These chemical reactions determine physical characteristics of animals • Genotype determines phenotype

  15. Transmission of Characteristics (cont.) • The Coding of Genetic Information • DNA • Composed of two deoxyribose strands • Phosphoric acid links deoxyribose in side strands • Side strands linked by nitrogenous bases • Nucleotide is combination of one nitrogenous base, one phosphate, and one deoxyribose

  16. Transmission of Characteristics (cont.) • The Coding of Genetic Information (cont.) • Factors that distinguish the DNA of one species from that of another • Number of AT and CG pairs • Sequence of these pairs • Whether the connections are AT, TA, CG, or GC • Number of base pairs present (length)

  17. Transmission of Characteristics (cont.) • The Coding of Genetic Information (cont.) • When cells divide, DNA is duplicated by semiconservative replication • RNA • Regulates protein synthesis • Primary function is to carry genetic message from DNA for protein synthesis

  18. Transmission of Characteristics (cont.) • Dominant and Recessive Genes • Dominant gene in heterozygous pair hides effect of its allele • Allele gene hidden is the recessive gene • Dominant gene usually represented by capital letter, recessive gene by lowercase letter

  19. Transmission ofCharacteristics (cont.) • Homozygous and Heterozygous Gene Pairs • Homozygous pair – one that carries two genes for a trait • Heterozygous pair – one that caries to different genes (called alleles) that affect a trait

  20. Transmission ofCharacteristics (cont.) • Six Basic Crosses • Six basic types of genetic combinations possible when one single gene pair considered • Multiple Gene Pairs • When more than one trait is considered, possible genotypes and phenotypes increase

  21. Transmission of Characteristics (cont.) • Incomplete Dominance • Alleles at a gene locus are only partially expressed • Codominance • Both alleles are fully expressed • Neither is dominant or recessive to the other

  22. Transmission of Characteristics (cont.) • Sex-Limited Genes • Only expressed in one sex • Sex-Influenced Genes • Dominant in one sex but recessive in the other • Sex Determination • Mammals: determined by male parent • Poultry: determined by female parent

  23. Transmission of Characteristics (cont.) • Sex-Linked Characteristics • Carried only on sex chromosomes • Linkage • Certain traits tend to appear in groups in offspring • The closer genes are located together on chromosome, the more likely they stay together

  24. Transmission of Characteristics (cont.) • Crossover • Chromosomes cross over one another and split to form new chromosomes with different combinations of genes • Mutation • A new trait appears in the offspring that did not exist in the genetic makeup of the parents

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