Bell Work

1. Bell Work • Breed out short legged dogs. Short is co-dominant with long legs • Start with a short legged dog (tt) and a long legged dog (TT).

2. Biology – Lecture 58 Natural Selection and Evolution

3. Darwin and Selective Breeding • At the time of publication, Darwin's ideas on selective breeding were considered to be controversial.

4. Why Were They Controversial? • Many believed that God had created and breathed life into every immutable variety of creature in its unchanging and perfect state.

5. Selective Breeding leading to Evolution • Darwin discusses selective breeding because it demonstrates in a familiar context that change through inheritance is possible and this is fundamental to the principle of natural selection or evolution.

6. Limitations to Selective Breeding Theories • The limitation is that selective breeding can only be carried out to preserve the outwardly visible characteristics which are considered desirable by the beholder. • Evolution or natural selection goes further than this.

7. Natural Selection is better than Selective Breeding • Natural selection recognizes that any variation which gives an animal an advantage over others of its kind will make that animal more likely to survive and therefore more likely to procreate. • It does not have to be outward appearances.

8. How is Selective Breeding Helpful? • Selective breeding supports the idea of inheritance and the struggle for survival suggests that only the fittest animals will survive and breed.

9. Selective Breeding and Natural Selection • Combining these ideas gives weight to the theory that only characteristics favorable to the species will be preserved, thus the species will evolve.

10. Results of Natural Selection • All species mutate over time (no species is immutable). • A species without desirable characteristics for survival in any particular environment will become extinct.

11. Darwin Combined with Genetics • Darwin only identified this process of evolution he could not explain inheritance. • It was the work on DNA carried out by Crick and Watson which completed Darwin's explanation (by adding the genetics portion).

12. Practice Breeding Out

13. Example 1 – Selective Breeding on X-linked Genes • Breed out hemophilia. (Remember hemophilia is an x-linked recessive gene). Start with a man with hemophilia and a woman without it.

14. Example 2 • White fur is recessive in tigers. A tiger breeder wants to only have tigers with orange fur (dominant). Show how he can breed out the white fur if he starts with a homozygous orange tiger and a white tiger.

15. Practice 1 • In rabbits, black fur is dominant over white fur. A breeder only wants white rabbits, but has a heterozygous black male and a homozygous white female. Cross them until only white rabbits remain.

16. Practice 2 • Tall is dominant over short in pea plants. Show the cross of a homozygous short plant is crossed with a homozygous tall plant. The breeder only wants tall plants.

17. Practice 3 • In humans, free-ear lobes are dominant to attached. Two parents that are both heterozygous free want to only have descendents with free ear lobes.

18. Practice 4 • Wrinkled seed are recessive to smooth seeds. A farmer has a homozygous wrinkled seed and a heterozygous smooth seeds producing plant. The farmer only wants wrinkled weeds.

19. Practice 5 • Blue eyes are dominant to red eyes in rabbits. A breeder has a heterozygous blue-eyed rabbit and a red-eyed rabbit, but only wants blue eyed offspring.

20. Practice 6 • In fruit flies, red eyes are dominant over white eyes. A breeder only has two white-eyed fruit flies. Can that breeder ever get red eyed fruit flies?