1. Animal Reproduction
AP Biology
Chapters 46

2. Why Reproduce?
To pass along DNA
To perpetuate the species

3. Not all animals have sex to reproduce, in fact, most animals use…
Asexual reproduction

4. Asexual Reproduction Genetic clones of parent Relies on mitosis Types:
Fission
Parent splits into two or more relatively equally sized offspring
Ex: sea anemone
Budding
One organism splits off of another
Ex: hydra
Fragmentation/regeneration
The body breaks into several pieces and is regenerated into an entirely new body
Ex: planaria

5. Advantages of Asexual Reproduction
No mate = no energy finding one or making gametes
Many offspring in a short time
Good for stable environments

6. Disadvantages of Asexual Reproduction
Lack of genetic diversity

7. Parthenogenesis Egg develops into zygote without sperm to fertilize it
Adults are haploid and produce eggs without meiosis
Bees, some fish, amphibians, and reptiles produced this way

8. For other animals….
sexual reproduction

9. Sexual Reproduction Involves the union of gametes from two parents
Complex mating behaviors surround sexual reproduction

10. External Fertilization
Occurs in moist environments (egg requires moisture)
Parents don’t usually make physical contact
Fish, amphibians
Disadvantages:
Zygotes are vulnerable
Low % of offspring to fertilized eggs produced

11. Internal Fertilization
Requires cooperative behavior
Mating behaviors evolved through natural selection
Requires organs to ensure sperm can meet egg
Advantages:
More protection for embryo (shelled eggs or develop inside mother)
More parental care

12. Advantages to Sex
Creates genetically diverse offspring, thus diverse populations
Beneficial in times of stress

13. Disadvantages of Sexual Reproduction
Fewer offspring produced per mating
It’s “expensive”
Must find a mate
Must expend energy making gametes
Must engage in competition for mates

14. Hermaphrodites Individuals with male and female reproductive systems
Most mate with another of the same species
Beneficial when members of opposite sex can’t be found
Ex: worms, slugs

15. Vertebrate Reproductive Tract
Most vertebrates have similar reproductive tracts
Exception:
Cloaca – common reproductive and digestive opening
Birds, reptiles, and amphibians

16. Human Reproductive Tract

17. Formation of male and female gametes
So many gametes, so little time…
Formation of male and female gametes

18. Spermatogenesis Begins at puberty Produces 4 viable sperm
Continuous, non-stop process
Occurring in the seminiferous tubule

19. Spermatogenesis Overview
Diploid spermatogonium go through mitosis; results in primary spermatocytes
Primary spermatocytes undergo meiosis (crossing over, independent assortment = variation!); result in secondary spermatocytes
Secondary spermatocytes undergo meiosis and produce immature spermatids
Spermatids mature into spermatozoa (sperm)
Sertoli cells provide nutrients to dividing cells

20. Some Fun Facts…
One spermatogonium = 4 haploid sperm at rate of 300 million per day
Sperm can live in the female reproductive tract for 48 hours
The head of the sperm contains enzymes to help it enter the egg
The midpiece has mitochondria to power the flagella
Semen contains million per mL (usually mL are released)
Of the total number released, less than 1% get close to the egg!

21. Hormonal Regulation of Male Reproduction
FSH stimulates meiosis of primary spermatocytes
LH stimulates interstitial cells to produce testosterone
Testosterone stimulates secondary spermatocyte meiosis, differentiation

22. Oogenesis Begins before birth; ends with menopause
Produces 1 viable egg per cycle

23. Oogenesis Overview
During fetal development, cells that will divide by meiosis differentiate in ovaries into oogonia (2n)
At the 3rd month of development, the oogonium forms a larger cell called a primary oocyte (2n)
Primary oocyte begins meiosis I but does not complete the process until after puberty
Cell is surrounded by cells called primary follicle
Primary follicles develop when signaled by FSH
Increasing FSH at puberty resumes meiosis in primary oocyte
One of haploid cells forms secondary oocyte; gets most of cytoplasm; remaining 3 become polar bodies
Secondary oocyte stops division at metaphase II until it is fertilized by a sperm
Secondary oocyte and polar bodies released at ovulation

24. Menstrual Cycles, Ovarian cycles, & Endocrine relations

25. Uterine Cycle
Series of changes to endometrium (inner layer of uterus) that occur monthly
Average cycle = 28 days (ranges from 24-35)
Menstruation (day 1-5)
Endometrium breaks down, is shed
Proliferative phase (day 6-13)
Endometrium rebuilds in preparation for implantation of a fertilized ovum
Secretory phase (day 15-28)
Endometrial thickening, glands are secretory

26. Ovarian Cycle
Monthly series of events associated with maturing and formation of a secondary oocyte and potentially an ovum
Follicular phase (day 1-13)
FSH secretion begins, follicle maturation occurs, estrogen secretion is prominent
Ovulation (day 14)
LH spike occurs, secondary oocyte released
Luteal phase (day 15-28)
LH secretion continues, corpus luteum forms, progesterone secretion is prominent

27. Hormone Control Uterine & Ovarian Cycles

28. If fertilization does occur…
Menstrual flow must be halted to keep the zygote
Corpus luteum produces estrogen and progesterone to maintain endometrium
Zygote releases HCG (human chorionic gonadotropin) that maintains the corpus luteum for about 3 months
HCG is what a pregnancy test tests for (that’s why you’ll never get a false positive!)

29. Pregnancy and Birth More hormones….
Estrogen and progesterone produced by developing placenta maintain pregnancy
High levels of estrogen trigger oxytocin production
Oxytocin stimulates uterine contractions (positive feedback) until baby is born
Relaxin loosens pelvic ligaments so baby can pass
Prolactin stimulates mammary glands to produce milk

30. Menopause Last menstrual and ovarian cycle
Decreased response in ovaries to LH and FSH
Decreased production of estrogen and progesterone