T2 - BIO - Preview 22 - 1N - Ploidy and recombination

Jan 6, 2025

Useful Genetics Lecture 1n: Ploidy and Recombination

Key Concepts

  • Ploidy Changes in Sexual Reproduction
    • Alternation between haploid and diploid cells
    • Introduction of new genome versions through recombination
    • Key processes: reassortment and crossing over

Essential Terms

  • Haploid Cell
    • Contains one complete set of chromosomes
    • Example: haploid set of N=5 chromosomes
  • Diploid Cell
    • Contains two homologous complete sets of chromosomes
    • Example: diploid set of 2N=10 chromosomes
    • Humans: N=23, hence diploid chromosome count is 2N=46
  • Ploidy
    • Not used to differentiate DNA amounts before and after replication
    • Identifies genetic constitution based on chromosome sets

Genetic Consequences of Sexual Reproduction

  • Alternation between haploid gametes and diploid organisms
  • Generation of new genetic combinations
    • Reassortment (Shuffling)
      • Inheritance of mixed chromosome sets from parents
      • New gametes contain mixed sets from maternal and paternal grandparents
    • Crossing Over
      • Creates genetic variation within each chromosome
      • Chromosome segments mix from maternal and paternal sources
      • Result in gametes with new combinations of segments

Process Descriptions

  • Reassortment
    • Chromosome shuffling like a deck of cards
    • New combinations in each generation
  • Crossing Over
    • Segments of chromosomes break and rejoin in new combinations
    • Increases genetic diversity significantly

Conclusion

  • Sexual reproduction involves changing ploidy levels
    • Gametes have one set; somatic cells have two sets
  • Generates genetic variation through reassortment and crossing over

Upcoming Topics

  • Genetic variation in populations
    • Connection to human evolution and interaction with Neanderthals
    • Further exploration in subsequent lectures