Factors of evolution

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Across
  1. 1. Interchanging of genes between population
  2. 4. Changes that occur in DNA sequences of an organism
  3. 6. A unit of heredity
  4. 7. Groups of actually or potentially interbreeding populations
  5. 9. Changing of allele frequencies in random samples
Down
  1. 2. Survival of the fittest
  2. 3. Number of offspring
  3. 5. A naturalist which explored the Galapagos islands
  4. 8. Change over time