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Unit 3: Genetics. Chapters 12. Objectives. Understanding of the formation of gametes & the role of DNA Knowledge of genotypic and phenotypic outcomes Mastery of mating, dominance, and incomplete dominance Role of Biotechnology in livestock systems. Gametogenesis.
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Unit 3: Genetics Chapters 12
Objectives • Understanding of the formation of gametes & the role of DNA • Knowledge of genotypic and phenotypic outcomes • Mastery of mating, dominance, and incomplete dominance • Role of Biotechnology in livestock systems
Gametogenesis • Takes place in the sex cells of the male & female • Male=spermatogenesis • Female=oogenesis • Cell division by meiosis • Cell Division by Meiosis 1 & 2 • Interphase-chromosomes duplicate • “Resting Phase” • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis
Spermatogenesis • 4 sperm are produced from each primary spermatocyte
Oogenesis • First division produces one large oocyte, and one smaller cell (polar body) • Second division results in one egg (ovum), and the second polar body • Polar bodies eventually die and get reabsorbed
Figure 12.3 Meiosis or reduction cell division in the testicle and ovary (example with two pairs of chromosomes). Source: Colorado State University.
Fertilization • Sperm & egg each provide one chromosome to each pair • Fertilized egg called a zygote • Zygote is diploid (two copies of each gene) • Gametes are haploid (one copy of each gene) • Each event is random, provides genetic diversity
Figure 12.4 Combining of chromosomes through fertilization (two pairs of genes used for simplification of example). Source: Colorado State University.
DNA • The genetic code for each animal is carried in the DNA • Deoxyribonucleic acid • Double helical structure • Location of each gene on the chromosome is called a locus
Figure 12.5 A simplified example showing a pair of chromosomes containing several pairs of genes. Source: Colorado State University.
Genes & Chromosomes • Genes & chromosomes are paired-homologous • Transmission of traits to offspring is entirely dependent upon which chromosomes are passed on • Sex Chromosomes • X & Y • Male carries both X & Y chromosomes • Female only carries the X chromosome
Genes & Chromosomes • Homologous chromosomes may differ in the way they influence a trait • Homozygous-if they have the same effect on a trait • Heterozygous-if they have a different effect on a trait • These traits are called alleles • One gene is always dominant while the suppressed gene is recessive • Genotype vs. Phenotype • Genotype refers to the genetic code of the trait • Phenotype is the trait that is expressed
Fundamentals of Mating • Homozygous dom. X Homozygous dom. • Homozygous dom. X Heterozygous • Homozygous dom. X Homozygous rec. • Heterozygous X Heterozygous • Heterozygous X Homozygous rec. • Homozygous rec. X Homozygous rec. • Mate using a Punnet Square
Gene Interaction • Dominance interaction exists when the dominant trait suppresses the recessive trait • Incomplete dominance refers to a phenotype that is expressed differently from the dominant and recessive phenotypes • Some heterozygotes are superior to homozygotes-Hybrid Vigor • Complete dominance, lack of dominance, overdominance
Figure 12.14 Bar graphs illustrating: (A) complete dominance; (B) lack of dominance; (C) overdominance.
Genetics & the Environment • Environment can influence the expression of a genetic trait • Give an example
Biotechnology • Genetic engineering • Superovulation • Sexing semen • Cloning • ET • Genetic markers • Gene therapy • Genetic selection • Artificial insemination
Biotechnology • Applications in genetic biotechnology • Genes can be removed, altered, and reinserted into an embryo in vitro • Genes can be modified or duplicated with the help of growth medium • bST • Genes from one specie can be inserted into another specie to enhance or alter a trait • Transgenesis • Nuclei can be taken from one individual an put together by Nuclear Fusion
Figure 12.15 A fertilized swine egg photographed at the moment it is microinjected with new genetic material. The vacuum in the large pipette at the bottom anchors the cell while a mixture containing the genetic material is forced through the smaller pipette into one of the egg’s pronuclei. Courtesy of R. E. Hammer and R. L. Brinster, University of Pennsylvania School of Veterinary Medicine.
Figure 12.16 Somatotropin production for use in cows and pigs.
