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