Do Now!! o Now What is the purpose of Mitosis? If a cell that has 12 chromosomes in interphase...

Do Now!! o Now

What is the purpose of Mitosis? If a cell that has 12 chromosomes in

interphase goes through mitosis, how many chromosomes will be in each cell?

How is a baby made? (on a CELLULAR level…)

Objectives

To list the steps of Meiosis. To compare and contrast Meiosis and

Mitosis. To explain why Meiosis is necessary.

MeiosisPurpose: to make sex cells

Gamete: sex cellMale gamete= spermFemale gamete= egg (ovum)

Somatic Cells vs. Gametes Somatic cells: non-sex

cells Our somatic cells contain

46 chromosomes: 1 chromosome from Mom

and 1 from Dad. These are called homologous chromosomes.

Each gamete (sex cell) contains only 23 chromosomes!

Why are there 46 chromosomes in our somatic cells?

Diploid vs. Haploid Diploid cell

Any cell with 2 homologous chromosomes

Abbreviated as 2n Ex: somatic cells

Haploid cell Any cell with a single

chromosome set Abbreviated as n Ex: gametes

How do we become a Diploid Zygote?Haploid egg cell fuses with haploid sperm

cell in a process called Fertilization.Half from mom and half from dad make up

our homologous chromosomes! (23 pairs)Our cells then undergo mitosis to create

us.But how did our parents create the sex

cells to produce us?

MeiosisTWO divisions!

Meiosis I and Meiosis II

Each are similar to mitosis

Produces 4 daughter cells

Phases are still IPMAT, however there are two of each of the PMAT phases.

Meiosis: 2 divisions Meiosis I:

Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 and

cytokinesis

Meiosis II: Prophase II Metaphase II Anaphase II Telophase II and

cytokinesis

Do Now!! What are somatic cells? Gametes?

If a somatic cell has a diploid number 2n=24, what is the haploid number?

List the steps of meiosis!

Objectives To list the steps of meiosis To describe each step of meiosis in

detail

Crash course biology!! https://www.youtube.com/watch?

v=qCLmR9-YY7o

Prophase I Pairing of

homologous chromosomes occurs forming a tetrad (synapsis)

Nuclear envelope breaks down

Crossing over can occur: homologous chromosomes exchange genetic material

Crossing Over

o Crossing over does NOT occur during mitosis

o Allows recombination of genes between chromosomes

o How is crossing over related to genetic variation?

Metaphase I Chromosome

centromeres attach to spindle fibers

Homologous chromosomes line up at the equator

Anaphase I Homologous

chromosomes separate and move to opposite poles

Telophase I and Cytokinesis

The spindles break down

Chromosomes uncoil, 2 new nuclei form

The cell divides

Prophase II

Chromosomes condense

Spindles form in each new cell

Spindle fibers attach to chromosomes

Metaphase II Chromosomes line

up at equator of each cell

Anaphase II The sister

chromatids are pulled apart at the centromere by spindle fibers

Move toward the opposite poles of the cell

Telophase II and Cytokinesis

The chromosomes reach the poles, and the nuclear membrane and nuclei reform

Spindles break down Cytokinesis results

in four haploid cells

Each with n number of chromosomes