Unit 3: Genetics
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Transcript of Unit 3: Genetics
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CHAPTERS 12
Unit 3: Genetics
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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
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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
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Spermatogenesis
4 sperm are produced from each primary spermatocyte
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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
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Figure 12.3 Meiosis or reduction cell division in the testicle and ovary (example with two pairs of chromosomes). Source: Colorado State University.
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Fertilization
Sperm & egg each provide one chromosome to each pair
Fertilized egg called a zygoteZygote is diploid (two copies of each gene)Gametes are haploid (one copy of each gene)Each event is random, provides genetic
diversity
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Figure 12.4 Combining of chromosomes through fertilization (two pairs of genes used for simplification of example). Source: Colorado State University.
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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
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Figure 12.6 DNA helix and structure of nucleotides.
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Figure 12.5 A simplified example showing a pair of chromosomes containing several pairs of genes. Source: Colorado State University.
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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
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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 recessiveGenotype vs. Phenotype
Genotype refers to the genetic code of the trait Phenotype is the trait that is expressed
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Fundamentals of Mating
Homozygous dom. X Homozygous dom.Homozygous dom. X HeterozygousHomozygous dom. X Homozygous rec.Heterozygous X HeterozygousHeterozygous X Homozygous rec.Homozygous rec. X Homozygous rec.Mate using a Punnet Square
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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
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Figure 12.14 Bar graphs illustrating: (A) complete dominance; (B) lack of dominance; (C) overdominance.
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Genetics & the Environment
Environment can influence the expression of a genetic trait
Give an example
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Biotechnology
Genetic engineering Superovulation Sexing semen Cloning ET Genetic markers Gene therapy Genetic selection Artificial insemination
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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
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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.
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Figure 12.16 Somatotropin production for use in cows and pigs.