Biology Study Guide

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Across
  1. 3. a change overtime
  2. 4. was oxygen free
  3. 6. egg and sperm
  4. 9. explains why something happens
  5. 11. only breeding desirable animals
  6. 14. the preserved remains of ancient organisms
  7. 15. sexual reproduction
  8. 16. used oxygen
  9. 17. do not have a nucleus or membrane
  10. 19. have a nucleus and a mambrane
  11. 20. help species survive in a specific environment
Down
  1. 1. the age of a fossil based on the other fossils
  2. 2. can reproduce healthy and fertile offspring
  3. 5. asexual reproduction
  4. 7. dominant and recessive
  5. 8. fertilized egg
  6. 9. constantly changing
  7. 10. the transfer of genetic variation
  8. 12. used to predict specific genotypes
  9. 13. eukaryotes evolved from prokaryotes
  10. 18. when two groups a species can no longer breed