Biology Review Crossword

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Across
  1. 1. Division The process by which a single cell splits into two identical daughter cells
  2. 3. both alleles are expressed at the same time in the appearance
  3. 5. trait that is always expressed whenever it is present
  4. 6. length of time required for half of radioactive atoms in a sample to decay
  5. 9. rule A=T G=C
  6. 13. dating uses half lives
  7. 14. selection humans choose the natural variations they like
  8. 15. scientist who studies fossils
  9. 16. selection changes in a population over time due to different levels of fitness
  10. 17. Era 65-245 mya, dinosaurs and small mammals lived
  11. 20. reduces chromosome number by half
  12. 21. trait that shows only if two copies are present
  13. 24. dating determines the age of the fossil by compared placement with fossils in other rocks
Down
  1. 1. tightly packed DNA wound around histone proteins
  2. 2. Cells with both sets of homologous chromosomes
  3. 4. can be joined in any order, any base sequence is possible
  4. 7. differences among individuals of the same species
  5. 8. any inherited trait that increases and organisms chance of survival
  6. 10. Single set of chromosomes
  7. 11. coiled and supper coiled mass of chromatin
  8. 12. photograph of fully condensed chromosomes lined up in pairs
  9. 18. daughter cells are identical to original cell
  10. 19. chart drawing that shows relationships in a family
  11. 22. ability of an individual to survive and reproduce in its specific enviornment
  12. 23. and Crick scientists who came to the conclusion that DNA is a double helix