TOPIC 6- Animal Reproduction and Development

diplontic animal life cycle

1. zygote produced through fertilization

   1. haploid gametes (sperm and egg cells)

2. embroyos are created- they are all full of yolk

   1. morula- solid ball of cell

   2. blastula= hollow, single-layer cell

   3. gastrula- three-layered embryo

3. larvae formed- looks different structurally from adult stage

4. juvenile ==> adult

   1. the only difference between juvenile and adult stage is maturity of reproductive organs

sexual reproduction

reproduction as a result of meiosis and recombination

• causes a lot of genetic variation because of the crossing over step in meiosis

asexual reproduction

gemmules

budding

fission

parthenogenesis

asexual reproduction without sperm, only eggs

hymenoptera

• queen is diploid and produces haploid gametes (meiosis)

• male bees are haploid and produce haploid sperm (mitosis)

• haploid egg from queen + haploid sperm = female bees (sexual reproduction)

• haploid egg = male bees (parthenogenesis)

daphnia

organism that can choose to produce sexually or asexually depending on threats from the environment

• sexual reproduction produces males- females make haploid eggs that get fertalized by males

  • when there is threat of population extermination

• asexual reproduction make females- females make genetically identical diploid eggs

  • when conditions are favourable

whiptail lizards

poultry

• males have ZZ gametes

• females have ZW gametes

  • whenever parthenogenesis occurs, a male is produced because females do not have the proper gametes to self-replicate (they need the W chromosome)

monoecious species

diecious species

oogenesis

1. MITOSIS: Germ cell undergoes mitosis into the oogonium. The oogonium undergoes mitosis again to make the 1º oocyte.

2. MEIOSIS I: The latter step takes place in the embryo. The 1º oocyte is arrested in prophase of meiosis I when ovulation does not occur. Once ovulation can occur at puberty, meiosis I goes to completion and now makes one polar body and a 2º aoocyte.

3. MEIOSIS II: The latter step takes place in a female that can undergo ovulation. The 2º oocyte is arrested at the metaphase of meiosis II, and can only go further once a sperm has entered. Once the sperm has entered, the 2º oocyte can resume to completion of meiosis II, wherein we get a second polar body an an ootid that can mature into an ovum

spermatogenesis

1. MITOSIS: Germ cells undergo mitosis into spermatogonial stem cell, which also undergo mitosis to become spermatogonium, which then undergo mitosis to become 1º spermatocyte, which has 2 sets of chromosomes with 46 chromosomes total. One set is from mom, one is from dad.

2. MEIOSIS: 1º spermatocyte undergo meiosis I to create 2º spermatocyte. 2º spermatocyte then undergo meiosis II to create early spermatids.

3. The early spermatids mature into sperm cells

fertilization

1. acrosome reaction breaks down jelly coat as the sperm embeds itself into the 2º oocyte

2. molecular recognition between the sperm and the ovum must occur to ensure species compatibility

3. the different nuclear membranes fuse as the sperm nucleus enters the 2º oocyte

   1. this prompts the 2º to finish maturation

4. cortical granules fuse with the egg plasma membrane and forms the fertilization envelope

5. nuclear fusion occurs and a zygote nucleus is formed

fast block

block to polyspermy that works immediately after the sperm enters the cell

• ions like calcium make the internal environment of the cell more positive which makes the membrane negatively charged

• this causes other sperm cells to be temporarily repulsed from the surface of the egg cell

external fertilization

internal fertilization

oviparity

ovoviviparity

viviparity

gastrulation

neurulation

endoderm

makes up the digestive tract, lungs, and urogenital tract

ectoderm

forms the epidermis and the central nervous system

mesoderm

forms muscles, skeleton, gonads, kidneys and dermis