Tiana Hobbs and Brandon Douglas4.2.3, 10.1-10.1.5

Assessment Statement 4.2.3,10.1.1,10.1.3Outline the process of meiosis, including pairing

of homologous chromosomes and crossing over, followed by two divisions, which results in four haploid cells.

Describe the behavior of the chromosomes in the phases of meiosis.

Explain how meiosis results in an effectively infinite genetic variety in gametes through crossing over in prophase I and random orientation in metaphaseI.

Overview Meiosis

Involves two divisions1st division called Meiosis IInterphase stage before Meiosis I which

includes G1, S, and G2 phases; similar to Interphase stages before Mitosis.

Short Interphase stage between Meiosis I and Meiosis II

Phases of Meiosis

Prophase I- within this stage, the chromosomes are becoming visible The homologous chromosomes pair up and crossing over occurs The nuclear membrane separates and the centrioles move to the poles of the cell

Metaphase I

Homologous chromosome pairs line up at equator of cell

Spindle fibers attach to chromosomes so that one chromosome from each pair is moved to each pole.

Anaphase IHomologous chromosomes separated and

pulled to opposite polesUnique number of chromosomes reduced to 23

from 46, although chromosomes are still composed of 2 sister chromatids.

Cell prepares for Cytokinesis

Telophase I

Each chromosome from each homologous pair are located at opposite poles

Nuclear membrane reforms around each daughter nucleus

Cell divides through cytokinesis

Meiosis II

Starts with two daughter haploid cells

Ends in the formation of four daughter cells, each with a haploid set of chromosomes.

Prophase II

Two daughter haploid cells present.

Nuclear membrane begins to break down

Spindle fibers form

Metaphase II

Chromosomes in each cell line up at equate of each respective cell

Spindle fibers attaches to the centromeres of each chromosome

Anaphase II

Chromosomes are divided at centromere as a result of the spindle fibers pulling each sister chromatid to opposite poles.

Sister chromatids then become chromosomes

Telophase II

Nuclear membranes form around each of the four sets of chromosomes

Cell divides through cytokinesis

Results in four daughter cells each with a haploid set of chromosomes.

Crossing Over Crossing Over

Prophase IForms chromatids with new combinations of

allelesRecombinants are chromatids with different

combinations of alleles than either parent chromatid

Crossing over occurs at a random pointMore than one chiasma can form per

homologous pair.

Random OrientationRandom Orientation

Metaphase IHomologous chromosomes line up at the equator in a

random orderMaternal or Paternal homologue can be pulled to

either poleTo calculate all variations you raise the number 2 to

however many chromosomes you are dealing with.For a human, the total variations are over 8 million.Combining that with the fact of crossing over, means

that there are almost an infinite number of genetic variations cause my meiosis.

Assessment Statement10.1.1Describe the behavior of the chromosomes in the phases

of meiosis.

The ChiasmataBefore the chiasmata can appear, the DNA of one

chromatid bonds together with the DNA of a non sister chromatid

Then, both the genetic information is transferred from both the father and mother (maternal and paternal chromosomes) this process is called crossing over

After the homologous chromosomes are no longer tightly connected, the chiasmata is formed and it links the homologous chromosomes pairs together until late metaphase I

Assessment Statement10.1.4State Mendel’s law of independent assortment

Mendel’s law of Independent Assortment

the transmission of traits to the offspring are independent to one another

When the chromosomes move to the opposite ends of the pole (of the equator) either chromosome can end up at a specific end

However, the movement of one chromosome to a pole does not affect the placement of the other

This connects to the law of independent assortment (Mendel’s) because when the homologous chromosome pairs separate, it allows the formation of daughter cells

Contributes to Genetic Variation

Works Cited"Animation: Random Orientation of Chromosomes

During Meiosis." Your Page Title. N.p., n.d. Web. 17 Feb. 2012. <http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__random_orientation_of_chro

"IB Biology Notes - Meiosis HL." IB Guides - Free International Baccalaureate study guides,

notes, videos and powerpoints.. N.p., n.d. Web. 17 Feb. 2012. <http://www.ibguides.com/biology/notes/meiosis->.