Asexual vs. Sexual Reproduction

1. Asexual vs. Sexual Reproduction

2. Asexual Reproduction

3. Asexual reproduction Asexual reproduction = one parent. The primary form of reproduction for single-celled organisms such as bacteria, and protists. Many plants and fungi reproduce mostly asexually as well.

4. Binary Fission Budding Fragmentation/ regeneration

5. Asexual Advantages Need only one individual to reproduce; can conserve energy No genetic change is “good” if environment is stable All individuals are producing offspring

6. Asexual Disadvantages No recombination of genes  An asexual population tends to be genetically static

7. Sexual Reproduction DNA from 2 individuals merge to form one Animals, Plants

8. Pollination Sexual Pollen is delivered to female part of plant Flowering plants + Plants don’t have to move, mixes DNA - Need external source for pollination to take place; wind, bee, bat, butterfly etc.

9. Sexual Reproduction

11. Sexual Reproduction Results in increasing genetic diversity of the offspring. Characterized by two processes: Meiosis - halving of the number of chromosomes in gametes Fertilization - combination of two gametes and the restoration of the original number of chromosomes

12. Sexual Reproduction • During meiosis, chromosomes usually cross over = genetic recombination. • Primary method of reproduction for the vast majority of visible organisms, including almost all animals and plants.

13. Advantages of Sexual Reproduction • Offspring are genetically unique from parents • Favorable when the environment is not stable • Slower rate of reproduction but faster evolution • Lower extinction rates

14. Disadvantages of Sexual Reproduction 1. Need two parents: must expend energy to find, identify (court), and copulate with mate  2. Genetic recombination is not necessary if conditions are stable  3. Only half the individuals are producing offspring- (Males are an energy issue)

17. Meiosis A Source of Distinction

18. from mom from dad child too much! meiosis reduces genetic content Meiosis Goal: reduce genetic material by half Why? n (mom) + n (dad) = 2n (offspring) Just right!

19. Why do you share some but not all characters of each parent? At one level, the answers lie in meiosis.

20. Keys to Understanding Meiosis Chromosomes are paired. Chromosomes carry genes.

21. Brown eyes Brown eyes Tall Tall Brown eyes Blue eyes Tall Short The forms of a gene on a pair of chromosomes may be identical .. or different.

22. Meiosis does two things 1) It takes a cell with two copies of every chromosome (diploid) and makes cells with a single copy of every chromosome (haploid).

23. This is a good idea if you’re going to combine two cells to make a new organism. This trick is accomplished by halving chromosome number. In meiosis, one diploid cell produces four haploid cells.

24. Diploid = 2n Haploid = n

25. Meiosis vs Mitosis

26. The second accomplishment: 2) Meiosis scrambles the specific forms of each gene that each gamete (egg or sperm) receives. This increases the variability of the possible gametes and leads to greater genetic diversity

27. Genetic diversity is important for the evolution of populations and species.

28. Increasing genetic diversity is accomplished through 2 ways • Independent assortment • Crossing-over.

29. Independent Assortment describes the way that the homologous chromosome pairs arrange themselves during the 1st metaphase.

30. Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes. In humans, n = 23 and 223≈ 8,000,0000. That’s a lot of diversity!

31. Crossing over describes how non-sister chromatids recombine during the 1st metaphase

32. Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.

33. Between Independent Assortment and Crossing-Over, No Two Gametes Are Identical.

34. “Putting It All Together” - Fertilization

35. Meiosis allows the creation of unique individuals through sexual reproduction.