Fundamental Principles of Genetics

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Fundamental Principles of Genetics

• Genetics study of heredity
• Gene determinant of heredity
• Chapter is outline of basic principles of genetics

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Cell Theory of Inheritance

• Plants and animals composed of cells
• Plant cell surrounded by cell wall
• Animal cell surrounded by cell membrane
• Nucleus location of chromosomes in cell
• Chromosomes carrier of genes

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Chromosomes

• Carriers of genetic material genes
• Occur in pairs
• Homologous chromosomes members of a pair
• Number of chromosomes constant among normal
  members of a species

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Chromosome Number

• Diploid (2N) numbers
• donkey 62 horse 64
• mule 63 swine 38
• sheep 54 cattle 60
• human 46 mink 30
• dog 78 cat 38
• chicken 78
• Normal cells have diploid (2N) number
• Gametes (sperm and egg) have haploid (1N) number

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Chromosomes

• Two major types
• Sex chromosomes one pair which influences sex
  of organism
• Autosomes all pairs other than sex chromosomes

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Sex Determination

• Mammals
• Sex chromosomes are
• female XX homogametic
• male XY heterogametic
• Chickens and turkeys
• Sex chromosomes are
• female ZW heterogametic
• male ZZ homogametic

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Chromosomal Abnormalities

• Changes in number of chromosomes
• Aneuploidy extra or missing chromosome
• Polyploidy extra or missing sets of chromosomes
• Usually lethal in animals
• Except aneuploidy of very small chromosomes (eg
  Down Syndrome in humans is extra 21)

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Chromosomal Abnormalities

• Changes in chromosome structure
• Deletion piece of chromosome removed
• Duplication piece of chromosome duplicated
• Translocation exchange of material between
  different chromosomes
• Inversion segment of chromosome reversed

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Chromosomal Abnormalities

• Changes in chromosome structure
• Cause loss of fertility
• Amount of loss dependent on type of change and
  importance of the affected segment of the
  chromosome

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Cell Division

• Two types
• Mitosis division of normal body cells
• Results in production of two identical diploid
  cells
• Meiosis division of germinal cells to produce
  gametes (sperm and egg)
• -Results in production of four different haploid
  cells

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Cell Division

• Mitosis
• Cell division of normal body cells
• Each daughter cell has same genetic complement as
  original cell

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Cell Division

• Mitosis
• Four phases
• Prophase Chromosomes become visible
• Metaphase Chromosomes line up across cell
  center
• Anaphase Sister chromatids separate
• Telophase Chromosomes condense and new nucleus
  is formed
• Interphase period between cell divisions
• Cytokinesis the actual division of the cell

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Mitosis

• 18. G2 Phase Preparation
• 19. Prophase
• 20. Metaphase
• 21. Anaphase
• 22. Telophase
• 23. Cytokinesis
• 24. G1 Phase - Cell Growth
• 25. S Phase - Replication

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Mitosis -- Meiosis
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Cell Division

• Meiosis
• Division in germinal cells to produce sperm and
  egg
• Each cell that results has 1N number of
  chromosomes (half of number of chromosomes in
  body cells

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Cell Division

• Meiosis
• Two cycles of
• Prophase
• Metaphase
• Anaphase
• Telophase
• Results in four cells with 1N number

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Cell Division

• Meiosis
• Spermatogenesis meiotic production of sperm
  cells
• Oogenesis meiotic production of egg cells

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The Gene

• Composed of DNA deoxyribonucleic acid
• Large double stranded polymer of units called
  nucleotides
• Nucleotide
• Sugar deoxyribose
• Phosphate group
• Nitrogeneous base
• adenine guanine
• cytosine thymine

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Transcription of RNA

• Bases in DNA code for transcription of RNA
• RNA ribonucleic acid
• Also nucleic acid
• Single stranded
• Uracil instead of thymine
• Ribose instead of deoxyribose

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RNA

• Three primary types of RNA
• Messenger RNA
• Transfers code from DNA to protein synthesis
• Transfer RNA
• Carries amino acids to the ribosome
• Ribosomal RNA
• Forms part of the structure of the ribosome

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Genetic Code

• Each amino acid coded by a three base sequence
  (codon)
• Most amino acids have more than one codon
• One codon specifies beginning of a protein
• Three codons specify the end of a protein

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Interactions Between Genes

• Epistasis
• Two or more gene pairs in which one gene pair
  influences expression of another gene pair
• Horned, polled, scurred
• Two gene pairs (horned vs polled) (smooth vs
  scurred)
• If horned scurred vs smooth does not matter
• If polled scurred vs smooth can express

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Genes and Embryological Development

• After union of sperm and egg
• Cell division occurs
• Early development - all cells are alike
• Subsequent development cells differentiate
• Embryological development is genetically
  controlled

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Genes and Embryological Development

• Lethal genes
• Genes which stop development
• Many must be received from both parents to cause
  death
• Cause of high percentage of embryonic death

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Biotechnology

• Biotechnology
• All technologies that pertain to molecular
  manipulation of living material
• Very difficult word to characterize
• Genetic engineering
• New methods for modifying the animal genome

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Transgenesis

• Transgenesis
• Movement of genes from one species into another
• First use development of mouse with extra genes
  for growth hormone

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Genetic Engineering in Plants

• Round-up-ready crops
• Several crop species have been engineered to be
  resistant to the herbicide Round-up
• Bt crops
• Corn and cotton have genes from a microbe that
  causes them to be resistant to corn borer and
  boll weevil
• Flavr-Savr tomato
• Gene altered to lengthen shelf life

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Cloning

• Clone genetic identical
• Identical twins are clones
• Cloning by embryo splitting has been available
  for several years
• Cloning from an adult DNA donor not possible
  until Dolly

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Cloning

• Dolly
• Developed at Roslin Institute
• Sheep cloned from cells from adult ewe mammary
  gland
• Cells had to be started over to remove results
  of cell differentiation

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Cloning

• Potential uses for cloning in animals
• Limited importance in routine livestock
  improvement
• Combine with transgenesis to produce animals with
  unique genetic makeup
• transgenesis to create first copy of animal with
  specific gene inserted
• cloning to make multiple copies of that animal

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Marker Assisted Selection

• Current selection
• Based on actual traits measured in animals
• Marker assisted selection
• Based on identification of genetic markers that
  are associated with performance traits
• Can be applied as soon as appropriate tissue
  (blood, skin etc) can be obtained
• Shortens time to obtain information for choosing
  superior parents

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Mutation

• Mutation change in the base sequence
• May result in change in amino acid sequence in
  protein
• May result in change in the phenotype
• Change is usually detrimental
• Only source of new genetic material

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Phenotypic Expression of Genes

• Phenotype Genotype Environment
• Gene action varies among different genes
• Dominance relationships vary widely

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Phenotypic Expression of Genes

• Dominant and recessive
• Color in Angus
• Genotype Phenotype
• BB Black
• Bb Black
• bb Red
• Black is dominant to red
• Red is recessive
• BB or bb homozygous
• Bb - heterozygous

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Phenotypic Expression of Genes

• Lack of dominance
• Color in Shorthorns
• Genotype Phenotype
• BB Red
• Bb Roan
• bb White
• Both red and white are expressed in heterozygote

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Sex-linked Inheritance

• Some genes on the sex chromosomes
• Inheritance pattern affected because males have
  only one X chromosome
• Hemophilia in humans
• Deficiency in ability for blood to clot

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Sex-influenced Inheritance

• Inheritance that is affected by sex of individual
• eg. scurs - dominant in males, recessive in
  females
• eg. horns in sheep dominant in males, recessive
  in females

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Sex-limited Inheritance

• Some traits express in only one sex
• Female
• Milk production, egg production, age at first
  estrus
• Male
• Scrotal circumference

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Genome Project

• Human Genome project
• Initiated by National Institutes of Health and
  Department of Energy
• Large multi-year, multi-location project to map
  the human genome
• Other genome projects
• Cattle, sheep, swine, horses, dogs, cats,
  turkeys, chickens, mice and many other species