I. Fertilization: Union of two reproductive cells (gametes). egg provides mitochondria, therefore mitochondrial DNA is from the mother.

II. Process of Development: embryonic development begins after sexual reproduction in plants and animals. The zygote becomes an embryo.

A. Types of development

1. Differentiation of cells into different types, different enzymes, and different structural proteins.

2. Growth: increase in overall size once food reaches embryo.

3. Formation of shape

a. induction: one set of cells influences development of others

b. programmed cell death

c. cell movement

B. Cleavage: process of a zygote dividing rapidly. little or no growth occurs.

1. morula: solid clump of cells.

2. blastocoel: fluid filled cavity that develops inside the morula. allows space for the movement of cells.

3. blastula: hollow ball of cells with a blastocoel.

4. cleavage patterns depend on the amount of yolk present. yolk stores energy and nutrients for the developing embryo.

a. spiral cleavage: newly formed cells are in a spiral pattern. (invertebrates)

b. insect cleavage: nuclei form, then plasma membrane laid down later.

c. radial cleavage: cleavage furrow divides into segments like an orange. (frog, bird, reptile, mammal)

d. little yolk: cells of the same size. examples: mammals, invertebrates

e. medium yolk: cleavage furrow passes through more slowly. animal pole (top) ahead, more small cells than vegetal pole (bottom). examples: frogs

f. large yolk: cleavage furrow cannot pass through, therefore egg cleaves only at the top. example: birds, reptiles.

C. Gastrulation: cells rearrange into distinct layers. animal takes on shape.

1. blastopore forms in the side of the blastula; cells from the surface move to the hollow interior.

2. gastrula: three-layered embryo (germ layers). cup shaped.

a. gastrocoel/ archenteron: central cavity. will become the lumen of the digestive tract.

b. ectoderm: will form neuroectoderm for nervous system and epidermis (skin, hair, nails, sweat glands). found in the animal hemisphere.

c. endoderm: cells filled with yolk lining (vegetal pole). gives rise to gut, digestive glands, internal structures.

d. mesoderm: at equator of egg. forms between endoderm and ectoderm. gives rise to muscles, skeleton, reproductive organs.

e. coelom develops later in the middle of the mesoderm. cell division, cell movement (singly or in sheets) induction.

D. Neurulation (3rd week in humans): development of the nervous system and head. two folds rise and join to form neural tube.

1. ectodermal cells form a neural plate which develops into a neural tube.

2. neural tube develops into brain and spinal cord.

3. further differentiation occurs and when complete, a period of rapid growth begins.

E. Extraembryonic membranes

1. chorion: outermost membrane that functions in gas exchange. in humans, it forms the fetal portion of the placenta.

2. amnion: delicate membrane that contains the amniotic fluid that bathes the embryo, protecting it from frying out and from mechanical shock.

3. allantois: storage area connected to the digestive region to collect metabolic waste productions in reptiles and birds. in mammals, allantoic blood vessels are part of the umbilical cord.

4. yolk sac: surrounds the yolk in bird and reptile eggs. in mammals, it is the first site of blood cell formation.

F. Organogenesis in Humans

1. Third week: nervous, digestive, and circulatory systems begin to form. heart begins to pulsate.

2. Fourth- fifth weeks: limb buds appear.

3. Fourth- twelfth weeks: heart, eyes, and brain develop.

4. Third month: movement begins. the most obvious progress is growth.

III. Differentiation and determination

A. Differentiation occurs when cells become specialized in structure and function. depends on location of different proteins in the egg and mother's genes producing protein gradients, some embryonic genes. genes can be switched on and off.

B. Determination: how the cell differentiates. based on which genes are expressed.

C. Indeterminate cleavage: develops normally even if cell is removed. determination begins after the 4-cell stage. can be divided vertically with no consequence because animal and vegetal poles are still equal.

D. Determinate cleavage: some determination at the first cell division.

E. Apoptosis: programmed cell death requiring protein synthesis. death of nerve cells, white blood cells.

F. Embryonic induction: fate of tissue determined by activity of own genes and the environment. one part of the embryo influences the development of another part of aembryo; chemical inducers like hormones can guide this process.

IV. Metamorphosis

A. Series of changes in body structure

B. Frogs

1. egg

2. larva (tadpole)

3. adult frog: approximately 3 months

C. Insects

1. Complete metamorphosis (butterfly)

a. egg

b. larva: worm-like appearance.

c. pupa: inside cocoon; tissues are reorganized.

d. adult

2. Incomplete metamorphosis (grasshopper)

a. egg

b. nymph: series of stages which look progressively more like the adult.

c. adult

V. Twinning

A. Identical twins: 1 egg, 1 sperm. same DNA.

B. Fraternal twins: 2 eggs fertilized by different sperm. different DNA.

V. Flowering plant development

A. Zygote divides into 2 cell

1. embryo

2. structure for transport of nutrients from parent to embryo

B. Food source

1. endosperm

2. cotyledons: once endosperm is used, leaf-like structures become the major food storage organs for the embryo.

C. Seed structures

1. hypocotyl: stlak-like part of embryo; forms stem and part of root.

2. epicotyl: attached at the upper end of the hypocotyl; forms a pair of leaves.

3. radicle: at the lower end of the hypoctyl; forms the root.

4. meristem; region of cell division.

D. Dormancy: seed is inactive until it is placed in a suitable environment.

E. Germination: development of seed into new plant.

1. radicle emerges from seed.

2. hypocotyl lengthens, forming the stem and upper root.

3. epicotyl emerges, forming leaves and part of stem.

4. cotyledons shrink

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