Meiosis
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.
Meiosis
Purpose: to make sex cells
Gamete: sex cell
Male gamete= sperm
Female 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?
Meiosis
TWO 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=qCL mR9-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
