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