Inheritance, Variation and Evolution

• Mitosis will lead to two identical daughter cells whereas meiosis will lead to four different daughter cells
• Mitosis


  Process used for growth or repair, results in diploid cells
• Meiosis


  Process used for sexual reproduction, results in haploid cells
• In mitosis, the chromosomes line up and divide into two identical daughter cells
• In meiosis, the chromosomes line up, undergo crossing over, and then divide into two and then four genetically different daughter cells
• Asexual reproduction is common in plants, bacteria, and fungi, resulting in genetically identical offspring
• Advantages of sexual reproduction

  • Genetically diverse population, better protection from diseases
• Disadvantages of asexual reproduction

  • Genetically identical population, susceptible to diseases
• Advantages of asexual reproduction


  • Only one parent required, energy conserved
• DNA is made of complementary base pairs (A-T, C-G) and has a sugar-phosphate backbone in a double helix structure
• Gene


  Stretch of DNA that codes for a characteristic
• Genome


  All the genes in a body
• Protein synthesis

  1. DNA sequence codes for amino acid sequence

  2. Amino acid chain folds into a specific protein structure
• Mutations in the DNA sequence can lead to changes in the protein structure and function
• Gamete


  Sex cell (sperm or egg)
• Allele


  Different version of a gene
• Dominant


  Only need one gene to express the characteristic
• Recessive


  Need two identical recessive genes to express the characteristic
• Homozygous


  Having two identical genes
• Heterozygous


  Having two different genes
• Genotype


  The genes an organism has
• Phenotype


  The observable characteristics of an organism
• Genetic cross


  Determine probability of inheriting a trait
• Genetic conditions


  • Polydactyly
  • Cystic fibrosis
• Advantages of embryo screening

  • Only healthy embryos implanted
  • Genetic match for sibling
• Disadvantages of embryo screening


  • Embryos created and destroyed
  • Religious objections
• Humans have 23 pairs of chromosomes (46 total)
• Females have two X chromosomes, males have one X and one Y chromosome
• Identical twins have the same genotype but different phenotypes due to environmental factors
• Causes of natural variation

  • Genotype
  • Environment
• Mutations occur during DNA replication and can be passed on, leading to evolution
• Natural selection


  Process where organisms with advantageous traits are more likely to survive and reproduce
• Charles Darwin proposed the theory of evolution by natural selection
• Evidence for evolution includes fossils, changes in bacteria, and geographic isolation leading to speciation
• Selective breeding involves choosing parents with desirable traits to produce offspring with those traits
• Speciation


  • Species of animals gets geographically separated
  • One species leads to various different species
• Speciation example


  • Darwin's finches in the Galapagos Islands
• Selective breeding


  Breeding an animal for a particular characteristic
• Animals that undergo selective breeding


  • Dogs
  • Cows
  • Horses
  • Cats
  • Chickens
• Genetic engineering


  Modifying DNA to produce desired characteristics