UNIT 3 PART 3: REPRODUCTION REPRODUCTION is the process by which living things produce more organisms of their own kind. There are two forms: Asexual and Sexual

ASEXUAL REPRODUCTION Because asexual reproduction uses the process of mitosis each offspring is identical to the parent. There is no change from generation to generation. Only one parent is needed. There are many types of asexual reproduction.

BINARY FISSION BUDDING Parent divides into two equal parts One celled organisms like bacteria, protozoa, algae, amoeba BUDDING Parent divides into two unequal parts Yeast, hydra, sponges, some worms

Sporulation – the formation of spores Single specialized cells produced by certain organisms that when released will germinate and grow into new individuals. Usually many released at one time from a single structure. Ex.: bread mold

Regeneration The ability to regrow lost body parts Hydra, planarian, starfish, earthworms, amphibians The more complex an organism is, the less likely it will be able to regenerate. Mammals can heal wounds, but not regrow limbs.

Vegetative propagation When roots, stems, or leaves gives rise to a new plant. The new plant will have the same characteristics as the parent plant. Natural ways: bulbs, corms, tubers, runners, and rhizomes. Artificial ways: a cutting of a leaf or stem, layering, grafting.

MEIOSIS AND SEXUAL REPRODUCTION Asexual reproduction requires only one parent cell that divides by mitosis and produces two genetically identical offspring. Sexual reproduction requires two parent cells from two separate organisms, or from two sexually different parts of a single organism, that combine to produce one offspring. These offspring are genetically different from each parent and from each other. Sexual reproduction produces variety.

In complex organisms special sex cells called gametes are produced by meiosis. Male gametes are called sperm and female gametes are called ova, or eggs. When the sperm and egg fuse, or join together, a new organism is formed. Fusion of the egg and sperm nuclei is called fertilization. The new cell formed is called a zygote.

Meiosis In meiosis the parent cell divides twice so there are four cells when it is finished. This cuts the chromosome number in half (2n  n). The normal 2n number is then restored during fertilization (n+n2n).

All cells in the body except gametes are called somatic cells. Every species has a certain number of chromosomes in every somatic cell. For example, humans have 46, fruit flies have 8. These chromosomes can be grouped into pairs of homologous chromosomes. Cells that have all these chromosomes are diploid (2n). Because gametes are produced by meiosis they have only one chromosome from each pair so they are haploid, or monoploid, (n).

The Big Difference in Meiosis Meiosis has the same steps as mitosis, only they happen twice to make four cells. During the first Prophase each pair of chromatids lines up with its homologous pair forming a group of four called a tetrad. During the first Metaphase the tetrads line up in the middle and the pair is split during the first division. This is when the chromosome number is actually cut in half.

Synapsis and Crossing-over Chromosomes line up as homologous pairs not as individual chromosomes. This is called synapsis. Sometimes during synapsis chromatids will bend and twist together and exchange similar sections. This is called crossing-over.

Oogenesis – the formation of eggs in the ovaries During both meiotic divisions the cytoplasm divides unequally. This results in one egg and three nonfunctioning polar bodies. Each cell is haploid and every egg is genetically different.

Spermatogenesis – the formation of sperm in the testes Each division produces cells of equal size. All four become functional haploid sperm. Every sperm is genetically different.

Four differences between Mitosis and Meiosis Asexual Forms 2 identical daughter cells Each daughter cell has the normal diploid (2n) number of chromosomes Occurs in all body cells Sexual Forms 4 non-identical gametes (sex cells) Each daughter cell has the haploid (n) number of chromosomes Occurs in ovaries and testes only

Fertilization is the joining of the sperm and egg nuclei to form a zygote. It restores the diploid (2n) species chromosome number. A fluid, water, must be present for the sperm to swim to the egg. This can happen externally in water like fish, or internally like birds and mammals. Fertilization

External Development in Water After fertilization the zygote must have food, water & the right conditions if it is to develop. Amphibian & fish eggs have no shell & little water. Food is in the yolk. They lay 100’s to 100,000’s of eggs, but have poor parental care.

External Development on Land Birds, reptiles & insects lay their eggs on land. The eggs have a shell for protection and contain all of the food and water that the embryo will need. They lay 1 to 100 eggs and have better parental care.

Internal Development Mammal eggs have no shell, little yolk or water. The embryo develops within the uterus and receives its food, water and oxygen from the mother through the placenta. They produce 1 to 10 eggs and have good parental care.

Marsupials These are animals like kangaroos whose babies develop in a pouch. Joeys are the size of a jellybean when they are born. They are pink, blind and hairless. They live in their mother's pouch drinking her milk.

Monotremes Monotremes are a strange mixture of mammalian, marsupial, & reptilian characteristics. Eggs are soft and leathery, like those of reptiles, but they are brooded in a marsupial-like pouch.