Sexual and asexual reproduction

Among living organisms, there are two types of reproduction-asexual and sexual. Each type of reproduction has advantages and disadvantages.

Sexual Reproduction Two parent cells join together to form offspring that are different from the parents. These parent cells are called sex cells and are different from ordinary body cells. Human body cells have 46 (or 23 pairs of) chromosomes. Sex cells have only 23 chromosomes, half of the usual number.

Sexual Reproduction Information contained on chromosomes determines many of our traits. Eye color Hair color Blood type Sex chromosomes determine gender. In humans, females carry two X chromosomes. Males have one X chromosome and one Y chromosome.

Sexual Reproduction Sex cells in females are called eggs and carry an X chromosome. Sex cells in males are called sperm and carry either an X or a Y chromosome. Egg and sperm combine to form either XX (female) or XY (male).

Sexual Reproduction The result: the offspring will carry half of each parent’s traits. Each time offspring are formed, a new combination of traits is passed. So, sexual reproduction produces offspring that have a different combination of traits than their parents and their siblings.

Sexual Reproduction Advantage- variation among offspring allows for adaptations and natural selection to occur. Disadvantage- organisms must find a mate in order to reproduce.

sexual reproduction in plants

Asexual Reproduction In asexual reproduction, a new organism (sometimes more than 1) is produced from only one organism. New organisms have the exact same DNA as the parent. This is known as Mitosis

Mitosis: Happens in all cells Cell division process 5 major stages

Prophase: Nuclear envelope disappears Chromosomes condense – can see sister chromatids and centromere Spindle forms

Prophase:

Metaphase: Chromosomes move to the equator of spindle Each chromatid is attached to spindle with centromere

Metaphase:

Anaphase: Centromeres split Sister chromatids are pulled apart to opposite poles of the cell Each chromatid is now a separate chromosome

Anaphase:

Telophase: Nuclear envelopes (2) reform Chromosomes begin to uncoil

Telophase:

Cytokinesis: Cytoplasm divides Two new daughter cells are now separate

Cytokinesis:

Organisms can asexually reproduce by: Budding- new organism grows from the parent. Examples- prickly pear cactus and potatoes.

Organisms can asexually reproduce by: Fission- single celled bacteria without a nucleus copies its genetic material and divides to form an exact copy of itself.

fission in bacteria

Organisms can asexually reproduce by: Regeneration- some organisms can grow an entirely new organism from a broken piece (sea stars for example).

Asexual Reproduction regeneration

Asexual Reproduction Advantage- no need to find a mate! Disadvantage- offspring are exact copies of their parents, so organisms don’t change much over generations. Doesn’t allow for adaptations and natural selection.

Meiosis:Terms you need to know  Zygote: The fusion of sperm and egg. Gamete: A mature male (sperm) or female (egg) germ cell that is able to unite with another of the opposite sex to form a zygote. Homologous Chromosomes: are chromosome pairs, one from each parent, that are similar in length, gene position and centromere location.

Meiosis Meiosis is a special type of cell division that produces gametes with half as many chromosomes. In sexual reproduction, two parents provide an offspring with an unique gene combination. Each parent gives 1/2 of his/her genes (Chromosomes) to the offspring.

Video Clip http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of%20Meiosis

Prophase 1 Homologous chromosomes pair up and form tetrad

Metaphase 1 tetrads of homologous chromosomes become attached to the spindle fibers and move to equator

Anaphase 1 Microtubules of the spindle fiber shorten and pull the chromosomes toward the poles, taking both sister chromatids with them.

Telophase 1 The nuclear membrane reforms around the daughter nuclei. Each daughter nucleus contains two sister chromatids for each chromosome, attached to a common centromere.

Prophase 2 Nuclear envelope breaks down and a new spindle forms.

Metaphase 2 Spindle fibers bind to both sides of the centromere.

Anaphase 2 Spindle fibers contract and the sister chromatids move toward the opposite side.

Telophase 2 Nuclear envelope reforms around the set of daughter chromosomes.

Four daughter cells are created with the perfect amount of DNA.

Video Clip http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio19.swf::Stages%20of%20Meiosis