Ch. 46—Animal Reproduction

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

Binary Fission

• Parent organism divides into two daughter organisms

• Used by prokaryoes (archaea and bacteria) as well as some protists and fungi

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

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

Parthenogenesis

• Unfertilized egg develops into a new individual• Examples: plants, invertebrates (some ants,

bees, and wasps), and some reptiles, amphibians, and fish

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)

Ovulation

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

Hermaphroditism

• Individual has both male and female reproductive systems

• Examples: snails, slugs, some fish, most plants

Sex Reversal

• Individual changes sexes during its lifetime

• Example: Bluehead wrasse– Females can change sex

and function as males

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

Gonads

• Organs that make haploid gametes

• Males = testes (produce sperm)

• Females = ovaries (produce eggs)

Male Anatomy

Spermatogenesis

• Production of mature sperm cells– Spermatogonia undergo

meiosis and develop into mature, motile sperm

• Occurs in seminiferous tubules

• Between the tubules are Leydig cells– Produce testosterone

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

Female Anatomy

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

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)