diversity and selection

• Meiosis


  Type of cell division that takes place in reproductive organs of multicellular, eukaryotic organisms
• Meiosis


  • Cells that undergo meiosis start as diploid and end up as haploid
  • Chromosome number halves during meiosis
• Meiosis


  1. DNA replicates

  2. DNA condenses into double-stranded chromosomes

  3. Homologous chromosomes pair up

  4. Homologous pairs separate

  5. Sister chromatids separate
• Meiosis in plants and other organisms produces haploid cells which then divide by mitosis to become gametes
• Without meiosis, sexual reproduction would not be possible as gametes would have the diploid chromosome number
• Crossing over


  Process where homologous chromosomes come together and exchange genetic material during meiosis I
• Independent segregation


  Random assortment of maternal and paternal chromosomes into daughter cells during meiosis
• Meiosis creates genetic variation in gametes through crossing over and independent segregation
• Mutations


  Changes in the DNA base sequence, including substitutions, deletions and insertions
• Mutations can alter the amino acid sequence of proteins and lead to changes in their structure and function
• Mutagens


  Agents that increase the rate of mutations, such as radiation, chemicals, and viruses
• Chromosome mutations can occur during meiosis when chromosomes fail to separate properly
• Genetic diversity


  The number of different alleles of genes in a species or population
• Genetic diversity allows a population to adapt to changes in the environment
• Genetic bottleneck


  An event that causes a large reduction in the size of a population, reducing genetic diversity
• Founder effect


  When a new population is started by a small number of individuals from a larger population, leading to differences in allele frequencies
• Natural selection


  Differential reproductive success leading to the increase in frequency of beneficial alleles in a population
• Types of adaptation


  • Behavioural
  • Physiological
  • Anatomical
• Directional selection


  Selection for extreme phenotypes
• Stabilizing selection


  Selection for intermediate phenotypes