Unit 10 - Meiosis

From Egg to Embryo – This photograph shows the After the

egg [shown in orange] is released from the ovary, it

travels into the fallopian tube. It stays there until a single sperm [shown in blue] fertilizes it. This

unit will explain the process of meiosis in the production of

eggs and sperm; summary color is blue and vocabulary words

are underlined.

What is meiosis?

Meiosis is the process by which the number of chromosomes is reduced by half forming gametes EX sperm or eggs. Two cell divisions Meiosis animation

http://www.wereyouwondering.com/wp ontent/uploads/2008/06/meiosisimagecreditnih.jpg

Meiosis vs Mitosis

Meiosis creates haploid cells; remember, you get half your DNA from each of your parents. Haploid, n = a cell with

only 1 copy of each chromosome; EX sex cells are haploid. Mitosis creates IDENTICAL diploid cells.

Diploid, 2n = a cell with 2 of each chromosome; EX somatic [body] cells like skin cells or heart cells are diploid.

"Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Science in Context. Web. 3 Dec. 2013.

Knowledge Check

How do the sketches to the

right visually represent a diploid

versus a haploid cell? Which is made

by mitosis versus which is made by

meiosis? Turn and talk to your neighbor.

http://www.personal.psu.edu/staff/d/r/drs18/bisciImages/haploidDiploid.png

Meiosis I The stages of meiosis I are identical to the stages of

cell cycle and mitosis; there are only slight differences during prophase.

After going through the steps of Meiosis I 1. Interphase 12. Prophase 1 [+ crossing over]3. Metaphase 14. Anaphase 15. Telophase 1 + Cytokinesis Forms 2 diploid daughter cells. …the cell divides again! [AKA Meiosis II]

"Meiosis." Biology. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010.Science in Context. Web. 3 Dec. 2013.

Homologous Chromosomes

AKA homologs are paired Xsomes with genes of the same trait in the same order; within each pair, one chromosome comes from each parent. Homologous chromosomes

are only found in a diploid cell.

"Result of Crossing Over." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Science in Context. Web. 3 Dec. 2013.

Homologs in a Karyotype

This a karyotype, a tool that geneticists use to look for mutations.

It groups the homologous chromosomes in pairs; the longest pair is #1, the shortest pair is #22.

http://www.biotechnologyonline.gov.au/images/contentpages/karyotype.jpg

What is crossing over?

During Prophase I, the homologous chromosomes mix genetic material [known as crossing over]. This is used to create new

combinations of genes – when the cell is split in two, the genetic material is now different than the parent cell due to crossing over.

Allows for more variety within organisms.

Crossing Over Animationhttp://

www.chuvicky.estranky.cz/img/picture/242/crossing_over.jpg

Knowledge Check

How do the sketches to the

right visually represent crossing

over. Turn and talk to your neighbor.

After meiosis I the cell divides again! This stage is different yet

again, because Xsomes are NOT copied during Meiosis II.

The stages are identical (interphase, prophase, metaphase, etc), but cells formed have half (haploid) of the number of Xsomes in the parent cells.

Forms unique 4 haploid daughter cells.

Meiosis Animation

http://rationalwiki.org/w/images/thumb/b/b4/Meiosis.gif/250px-Meiosis.gif

Meiosis II

Exit Ticket (Not a Turn and Talk)

"Mitosis and meiosis." World of Anatomy and Physiology. Gale, 2010. Science in Context. Web. 4 Dec. 2013.

Name & Period at the Top

What are the similarities and

differences between the processes of

mitosis and meiosis?

List your answer in bullet points on

your sticky note.

Visualizing the Process Use the play dough and

the chalk to show meiosis at your tables. Our organism only has 2

chromosomes; use two colors [do not completely mix them].

Show the following: Meiosis 1 Stages Crossing over Meiosis 2 Stages +

Cytokinesis Label the following:

Diploid cell Haploid cell

Knowledge Check

How many chromosomes are at the beginning of the diagram versus at

the end? Based on that information, how many would go in each haploid daughter cell? Turn and talk to your

neighbor.

Nondisjunction

During meiosis, if homologous chromosomes fail to separate correctly during anaphase (nondisjunction) then gametes have either extra Xsomes or they are missing chromosomes. These mutations are passed on during fertilization

[see image to the right]. Offspring with more than the usual #

of Xsomes are called polyploids. ▪ Rare in animals, sometimes causes death. ▪ Common in plants; polypoids are often healthier.

Example of Polyploidy

One of the most common examples of polyploidy in humans is Trisomy

21 [extra copy of chromosome 21]. These individuals have Down

syndrome.

http://www.geneticsofpregnancy.com/images/Down_syndrome.jpg http://static3.wikia.nocookie.net/__cb20

120608112249/glee/images/9/98/Becky_Jackson.png

Knowledge Check

How do the sketches to the

right visually compare normal

meiosis versus nondisjunction. Turn and talk to your neighbor.

"Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson. New York: Macmillan Reference USA, 2010. Science in Context. Web. 3 Dec. 2013.