tiana hobbs and brandon douglas 4.2.3, 10.1-10.1.5
DESCRIPTION
Overview Meiosis Involves two divisions 1 st division called Meiosis I Interphase 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 IITRANSCRIPT
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->.