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