Sexual Reproduction and Meiosis

Sexual Reproduction• How new organisms are produced

• 2 new cells come together

• Formed from cells in reproductive organs

Sex Cells in Humans• Male reproductive organs contain sex

cells called sperm

• Female reproductive organs contain sex cells called eggs

Meiosis I• Chromosomes become

duplicated

• There are 4 Phases: Prophase I, Metaphase I, Anaphase I and Telophase I

Prophase I• Duplicated chromosomes are

visible under a microscope as a chromatid

• Duplicated chromosome comes near its duplicated mate

Metaphase I

• Duplicated chromosome pairs line up in center of cell

• The centromere of each pair becomes attached to one spindle fiber

• The chromatids do not separate

Metaphase I

Anaphase I

• 2 pairs of chromatids move away to opposite ends of the cell

• Duplicated chromosome still have 2 chromatids

Telophase I

• The cytoplasm divides

• 2 new cells form

• New cell has 1 duplicated chromosome from each similar pair

Telophase I

Meiosis II

• Begins after 2 new cells form in Meiosis I

• Chromatids of each chromosome will be separated during this division

• Occurs in 4 phases: Prophase II, Metaphase II, Anaphase II, Telophase II

Prophase II

The duplicated chromosomes and spindle fibers reappear in each new cell

Metaphase II

• Duplicated chromosomes move to the center of cell

• Each centromere attaches to 2 new spindle fibers

Anaphase II

• Centromere divides

• Chromatids separate and move to opposite ends of the cell

• Each chromatid is now an individual chromosome

Telophase II

• Spindle fibers disappear

• Nuclear membrane forms around the chromosomes at each end of the cell

• Cytoplasm divides

How Fast Does Meiosis Happen?

• Just how fast does meiosis happen?

• Is it faster than a car going 100 mph or is it slower than a turtle crawling?

• Lets find out!

Meiosis! Meiosis! Meiosis!

• Now that you are an expert on Meiosis, let’s see how well you can identify each step

• Name each of the following steps from Meiosis I or II.

Name this step.

Metaphase 2!That’s right!

Which step is this?

Telophase I!That’s right!

Is this step from Meiosis I or II?

Meiosis I!That’s right!

Meiosis!

• Cells have been divided, chromosomes duplicated, we have reached the end of meiosis….

• See you next class!

Webliography

• Pictures taken from Microsoft Clip Art• http://www.sumanasinc.com/webcontent/

animations/content/meiosis.html• http://www.uic.edu/classes/bios/bios100/

lecturesf04am/prophase1m.jpg• www.biologycorner.com/bio1/qz_meiosis.html• Information taken from Glencoe LifeScience Book A• http://videos.howstuffworks.com/hsw/5988-mitosis-

and-meiosis-metaphase-one-video.htm• http://www.usd.edu/~bgoodman/cell.JPG