M EIOSIS Recap of Asexual Reproduction n One

M EIOSIS

Recap of Asexual Reproduction n One parent Genetically identical offspring One organism can have many offspring

Sexual Reproduction n Multicellular organisms that reproduce sexually have two types of cells: n Somatic Cells Body cells, reproduce via cell division (Mitosis) n Human somatic cells have 23 pairs of chromosomes (46 total) n n Sex Cells (Gametes) n Have half the chromosomes of the parent cell (23 total)

Sexual Reproduction n Involves sex cells joining to produce a zygote

Sexual reproduction n Requires two parents, a male and female.

Sexual reproduction n Both have sex organs

Sexual reproduction n The sex organs make sex cells (gametes)

Sexual reproduction n In male animals the sex cells are called sperm, made in sex organs called testes (testis is singular)

Sexual reproduction n In female animals the sex cells are called eggs, made in sex organs called ovaries. An egg is released from the ovaries about every 28 days. This is called ovulation.

Sexual reproduction n During sexual reproduction the sperm and egg join together (fertilization)

External fertilization In some animals fertilization takes place outside the body.

Chromosome Numbers n Individuals from the same species have the same number of chromosomes Goldfish have 94 chromosomes n Fruit flies have 8 chromosomes n Humans have 46 chromosomes n

So…. n n If sexual reproduction involves the fusing of genetic material from TWO individuals, then why doesn’t the resulting offspring contain twice the number of chromosomes? The process that produces sex cells which have half the number of chromosomes as the parent = MEIOSIS

Meiosis n n Meiosis ONLY happens in the cells that produce gametes (reproductive cells) Meiosis sometimes called “reduction division” Reduces the chromosome number by half n Example: Human Somatic cells have 46 total n chromosomes; sex cells have 23 total chromosomes (half)

Meiosis n n Cells with half the chromosome number of the parent are called haploid (n) Cells that have a complete set of chromosomes are called diploid (2 n)

When do we produce sex cells? n n Males produce sperm continuously after puberty. Women produce all of their eggs when they are developing as a fetus. n n They are produced and stored in the ovaries. One egg completes its development once a month after puberty.

How do we produce new sex cells? n n The cell replicates its genetic material. The nucleus divides twice, producing 4 nuclei. The cell divides into 4 new cells. These then specialize to form sperm or ova.

Meiosis The process by which a cell replicates its DNA, then undergoes 2 nuclear divisions to form haploid sex cells.

Meiosis Phases n Two different phases Meiosis I n Meiosis II n n Very original…

Meiosis Phases n n Meiosis I Two daughter cells (a little different though compared to mitosis) Meiosis II Four daughter cells produced

https: //www. youtube. com/wat ch? v=to. WK 0 f. Iy. Fl. Y

What happens in meiosis n n This cell contains one pair of chromosomes. Our body cells contain 23 pairs.

What happens in meiosis? n n The DNA in each chromosome replicates. Each chromosome now has an identical copy attached.

What happens in meiosis? n Some chromosomes exchange different versions of their genes (eg blue eyes for brown eyes).

What happens in meiosis? n n The nuclear membrane breaks down. The pairs of each chromosomes are pulled apart.

What happens in meiosis? n The copies of each chromosome are then pulled apart.

What happens in meiosis? n n n 4 new cells are made. They contain half the original number of chromosomes. These can now specialize to form sperm or eggs.

Stop-Motion Project n n In groups of 3 You will create a stop-motion video on the process of Meiosis n n Stop motion = a ton of pictures strung together to make a video Use your phone to create a stop-motion using a specific app

Stop-Motion Project n n Today, you will create a storyboard with your group so that next day we can start processing our stop motion videos Supplies provided: Playdoh (bring some if you have any!) n Random assortment n n https: //www. youtube. com/watch? v=w. Vj. M FU 11 h. VA