Genetic foundations

• Mendel's Principle of Segregation


  During gamete formation, alleles segregate so each gamete carries only one allele per gene
• Mendel's Principle of Independent Assortment


  During gamete formation, genes for different traits segregate independently of each other
• True Breeding


  Organisms that produce offspring of the same variety over many generations
• Cross Breeding


  Breeding between different parental types to produce hybrids
• F1 generation


  The first generation offspring resulting from a cross
• F2 generation


  The second filial generation from breeding F1 offspring
• Locus


  The specific location of a gene on a chromosome
• Homozygous


  Has two identical alleles
• Heterozygous


  Has two different alleles
• Dominant Allele


  An allele that is always expressed, masking the recessive allele
• Recessive Allele


  An allele that is only expressed when the dominant allele is absent
• Phenotype


  The observable physical characteristics of an individual
• Genotype


  The genetic makeup of an individual, including expressed and unexpressed alleles
• Assumptions made under Mendelian genetics

  • Genes have two alleles
  • One allele dominant over the other
  • Different chromosomes
  • No gene interactions
• Mendelian genetics with multiple alleles


  They can show varying degrees of dominance and recessiveness forming a spectrum
• Incomplete Dominance


  Neither allele fully masks the other, resulting in an intermediate phenotype
• Co-Dominance


  Both alleles contribute to the phenotype in distinguishable ways
• Outcome of meiosis in most protists and fungi


  First cells of the next generation
• Sexually reproducing organisms produce haploid gametes at some point in their life cycle
• Fertilization


  Fusion of two haploid gametes to form a zygote
• The zygote obtains half of its chromosomes from each gamete
• Fusion of gametes during fertilization restores the diploid number and homologous chromosomes</b>
• Cells produced by meiosis in animals

  Haploid sex cells
• The only haploid cells in animals are egg or sperm
• Maturation processes of egg and sperm cells in animals


  Oogenesis and spermatogenesis
• Fertilization in animals


  Zygote grows by mitosis producing the adult stage
• Animal life cycle


  Diploid life cycle
• Fusion of haploid gametes in protists and some fungi


  Zygote immediately undergoes meiosis forming single haploid cells
• The nucleus state in protists after zygote formation is haploid
• Single cells in protists decide to become gametes or undergo mitosis to make more individuals asexually
• Alternation of generations in plants

  Having both haploid and diploid multicellular stages
• Products of meiosis in plants

  Haploid cells called spores
• Spores in plants


  Grow into multi-cellular haploid structures called gametophytes
• Gametophytes in plants eventually produce gametes
• The predominant stage in the life of a plant, sporophyte or gametophyte, varies with different types of plants
• Asexual reproduction


  A good strategy for a species in a consistent environment
• Species without sexual reproduction lack genetic variation to adapt to change
• Interphase


  The phase of meiosis where chromosomes duplicate
• Synaptonemal complex


  Joins the sister chromatids of chromosomes in prophase I of meiosis
• Crossing over in meiosis


  Exchanges fragments between homologous chromosomes creating new genetic combinations