Rucete ✏ Biology In a Nutshell
1. What Is Genetic Variation?
- Genetic variation refers to differences in DNA sequences among individuals within a population.
- It is essential for evolution and adaptation through natural selection.
2. Sources of Genetic Variation in Meiosis and Sexual Reproduction
a) Crossing Over (Prophase I of Meiosis)
- Homologous chromosomes exchange segments of DNA.
- Produces new combinations of alleles on each chromosome.
b) Independent Assortment (Metaphase I of Meiosis)
- Homologous chromosome pairs align randomly at the metaphase plate.
- Results in many possible combinations of maternal and paternal chromosomes in gametes.
c) Random Fertilization
- Any sperm can fuse with any egg, producing unique zygotes.
- Increases the number of possible genetic combinations exponentially.
3. Genetic Variation in Life Cycles
Humans (Animal Life Cycle)
- Zygote (2n) → Multicellular organism (2n) → Gametes (n) → Fertilization → Zygote (2n)
Fungi
- Zygote (2n) → Meiosis → Multicellular organism (n) → Gametes (n) → Fertilization → Zygote (2n)
Plants (Alternation of Generations)
- Zygote (2n) → Sporophyte (2n) → Meiosis → Spores (n) → Gametophyte (n) → Gametes (n) → Fertilization → Zygote (2n)
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Biology in a nutshell