Ch. 46—Animal Reproduction

1. Ch. 46—Animal Reproduction

2. Asexual Reproduction • Offspring arise from a single parent and inherit the genes from that parent only • Does not involve meiosis or fertilization • Primary form of reproduction for single-celled organisms (such as archaea, bacteria, protists) and some plants and fungi

3. Binary Fission • Parent organism divides into two daughter organisms • Used by prokaryoes (archaea and bacteria) as well as some protists and fungi

4. Budding • Offspring splits off of parent resulting in a ‘mother’ that is larger and a ‘daughter’ that is smaller than the parent • Examples: yeast, hydra, potatoes • Buds grow into fully matured individuals and eventually break away from parent

5. Fragmentation • New organisms grows from a fragment of the parent • Each fragment develops into a mature, fully grown individual • Examples: annelids, sea stars, fungi, plants, lichen

6. Parthenogenesis • Unfertilized egg develops into a new individual • Examples: plants, invertebrates (some ants, bees, and wasps), and some reptiles, amphibians, and fish

7. Sexual Reproduction • Creation of a new organism be combining the genetic material of two individuals • Meiosis (halving of the number of chromosomes; haploid gametes) • Crossing over (recombination) • Fertilization (fusion of two gametes, the ovum and the sperm to produce a diploid zygote)

8. Ovulation • A mature ovarian follicle (collection of cells containing an oocyte) ruptures and discharges an ovum (aka oocyte, female gamete, or an egg)

9. Hermaphroditism • Individual has both male and female reproductive systems • Examples: snails, slugs, some fish, most plants

10. Sex Reversal • Individual changes sexes during its lifetime • Example: Bluehead wrasse • Females can change sex and function as males

11. Fertilization • Union of egg and sperm • External fertilization • Eggs are shed by female • And male releases sperm on the eggs • Happens externally (outside the body), usually in water • Examples: coral, hydra, sponges, most fish • Internal fertilization • Sperm are deposited in female reproductive tract, where fertilization occurs • Can occur in dry environments • Examples: some fish, most reptiles & birds, all dinosaurs and mammals

12. Gonads • Organs that make haploid gametes • Males = testes (produce sperm) • Females = ovaries (produce eggs)

13. Male Anatomy

14. Spermatogenesis • Production of mature sperm cells • Spermatogoniaundergo meiosis and develop into mature, motile sperm • Occurs in seminiferous tubules • Between the tubules are Leydig cells • Produce testosterone

15. Oogenesis • Development of mature ova • Oogonia multiply, undergo meiosis, stop at prophase I of meiosis I and are now called primary oocytes • From puberty until menopause, FSH stimulates a follicle to grow and its primary oocyte to complete meiosis I and II, after which is called a secondary oocyte

16. Female Anatomy

17. Menstrual Cycle • Other mammals have estrous cycles • Vagina is receptive to mating • Primates have a menstrual cycle • 3 phases: • Menstrual flow phase (day 1-5)—endometrium is shed • Proliferative phase (day 6-14)—endometrium regenerates and thickens • Secretory phase (day 15-28)—endometrium continues to thicken; if embryo has not implanted, menstruation begins

18. Ovarian Cycle • Follicular Phase (day 1-14) • Follicle grows and matures (follicle includes support cells and the oocyte) • FSH and LH stimulate follicle to grow and mature • Follicle cells also produce estradiol (an estrogen that promotes thickening of endometrium) • Ovulation (day 14) • Oocyte is released from the follicle and ovary to the fallopian (uterine) tubes • Triggered by surge in LH • Luteal Phase (day 15-28) • Remaining follicle cells grow in the ovary and form the corpus luteum • Corpus luteum secretes progesterone and estradiol (maintains the endometrium during pregnancy) • Corpus luteum then degenerates if egg is not fertilized • Sharp decline in estragiol and progesterone lead to shedding of endometrium)