Chapter 11-4: MeiosisProduction of Sex Cells

Introduction

• Mitosis and Meiosis are somewhat similar, but have 2 completely different goals.

• Mitosis used in growth, healing, and reproduction in unicellular organisms. Whereas, Meiosis is SOLELY used for the production of gametes (sex) cells in multicellular organisms.

M

End Result:2 identical daughter cellsFinish: 2n

End result:4 genetically different daughter cellsFinish: n

Process:1 round of division.Start: 2n

Process:2 rounds of divisionStart: 2n

Mitosis MeiosisVS.

•Humans have two full sets of chromosomes • (one set from our male parent and one from our female parent.)

• Each pair of chromosomes are known as “homologous” because they share the same genes, but likely very different alleles.

Ploidy: How many sets of chromosomes an organism has.

• Because we (humans) have two complete sets of chromosomes, we are said to be diploid.

The diploid number is referred to as 2N. For humans, 2N = 46.

Each human somatic or body cell contains 46 chromosomes.

Ploidy

Human Karyotype

Homologous pair

Each human gamete or sex cell only has a single set of chromosomes and are referred to as haploids.

Ploidy

Human Karyotype

http://www.acmecompany.com/stock_thumbnails/13217.forty-six_chromosomes.jpg

EGG + SPERM

http://www.angelbabygifts.com/Image by Riedell Image by Riedell

n n 2n

haploid haploid diploid

For our sperm or eggs, the haploid number is 23.

________ = _______ (sperm and eggs)

________ = _______ (every other cell in our body)

n 23

2n 46

How are haploid (N) gamete cells produced from diploid (2N) cells?

Meiosis is a process of reduction and division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.

The Process of Meiosis - click

http://www.tokyo-med.ac.jp/genet/anm/mimov.gi

Watch carefully!

Diploid number?

4 chromosomes

Homologous pairs?

2 pairs

By the end of G2, meiosis is ready to

begin.

http://www.biostudio.com/d_%20Meiotic%20Recombination%20Between%20Linked%20Genes.htm

End of Meiosis I:

If female – the process pauses here until the menstrual cycle begins during puberty. Once a month, one egg is released and may

entire Meiosis II if fertilized.

If male – the process does not pause, it goes right into Meiosis II. No time wasted to make sperm!!

Notice how meiosis differs between males and females.

Spermatogenesis: Creates 4 genetically different sperm

• Occurs in testes

• Prompted by testosterone

• Creates 4 cells

Spermatogenesis – creation of sperm

Oogenesis: Creates 1 viable egg and 3 polar bodies that are digested by lysosomes.

Notice how meiosis differs between males and females.

Oogenesis

• Occurs in ovaries

• Born with a finite number of primary oocytes

• Creates 1 egg and 3 polar bodies

Sperm structure

Timeline

Mitosis resulted in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells.

Summary of MITOSIS: (Genetically Identical)Mitosis allows an organism's body to grow and replace cells. In asexual reproduction, a new organism is produced by mitosis of the cell or cells of the parent organism.

Summary of MEIOSIS: (Genetically Different)A diploid cell but produces four haploid (N) cells. These cells are genetically different from the diploid cell and from one another. Meiosis is how sexually reproducing organisms produce gametes.

EGG + SPERM

http://www.angelbabygifts.com/Image by Riedell Image by Riedell

_ n __

haploid ________ diploid

http://www.youtube.com/watch?v=6z3tafuoN0k National Geographic in the womb. Start at 5:30