Download Chapter 12: Cell ASEXUAL Reproduction (MITOSIS) Section 1

Chapter 12: Cell ASEXUAL Reproduction (MITOSIS)
Section 1: Three functions of cell division: cell replacement (skin cells) (MAINTENANCE); growth (embryos);
asexual reproduction (growing new parts from fragmented pieces, like star fish).
Know that the number of chromosomes do not correspond to what size the animals are.
Section 2: DNA packaging/FOLDING. DNA is wounded as a double helix, then added are Histones
(proteins) making Chromatin. The chromatin wounds making a Nucleosome Complex. Next, the
nucleosomes wind further making a tight fiber, making Loops. This all then makes the Chromosome,
specifically sister chromatids, with a centromere in the middle which is a pinching in the middle, it’s like
a “waist.”
Section 3: Cell Cycle (it links with Section 3, Mitosis which is Asexual Reproduction)
The cycle is the life of the cell, which are the steps of Mitosis. Mitosis is the parent cell gives its identical
chromosomes to the 2 daughter cells. 1N > 2N > 1N
IPMAT: MITOSIS






~90% of the time the cell is in INTERPHASE = cell growth, nuclear envelope is intact, chromatin
exists, centrosomes w/microtubules exist. There are 3 points to Interphase: G1 (growth 1), S (DNA
synthesis), G2 (growth 2). There are start/stop signals (like red/green lights), at G1 and G2, that tell the
cell to either continue or stop the cycle. If there is a damaged cell, the stop signal will stop the cycle.
However, if it is a cancer cell, it will ignore the stop sign and continue making cancer cells (1N
chromosomes)
PROPHASE = chromatin coils to make sister chromatid chromosomes. The nuclear envelope
disappears. The microtubules/spindles grow & attach to centromere. More cell growth. (2N
chromosomes)
~10 % of the time in MITOTIC PHASES: M, A, T.
METAPHASE = the sister chromatids line up in the middle, the microtubules attach to the centromeres.
ANAPHASE = the sister chromatids separate to either pole of the cell, still attached to the microtubules.
TELOPHASE = Cleavage Furrow occurs where the cell starts pinching off; Cytokinesis occurs, where
the cytoplasm divides. Now we are left with 2 daughter cells that have identical genes to the Parent. (1N
chromosomes each)
Plant cells also go thru cytokinesis, but make a cell plate, which makes a new cell wall.
Know definition of karyotype, somatic cell (autosomes/body cells), & sex cells (gametes, like egg cell or sperm
cell).
CHAPTER 13:
MEIOSIS HAS 2 STAGES: I & II. Know haploid (1N) & diploid (2N). Know definition of gametes,
fertilization, & zygote. Basic idea of Meiosis










INTERPHASE I = Just like Mitosis Interphase. (2N) G1, S, G2
PROPHASE I = Instead of sister chromatid, now HOMOLOGOUS CHROMOSOMES PAIR UP.
Crossing over can occur here. The exact spot crossing over occurs is called the CHIASMA.
METAPHASE I = Homologous pairs line up in the middle.
ANAPHASE I = Homologous pairs split to either side. Thus now they are sister chromatids on either
side.
TELOPHASE I = cleavage furrow & cytokinesis; now each daughter cell has sister chromatids. (2N)
NO INTERPHASE II. Now Stage II is like Mitosis (because everything is sister chromatids from now)
PROPHASE II = microtubules grow, nuclear envelope disappear…
METAPHASE II = sister chromatids now line up in the middle (don’t forget the word: metaphase plate),
and microtubules attach at the centromere.
ANAPHASE II = sister chromatids separate.
TELOPHASE II = cleavage furrow & cytokinesis. Now 1N in four daughter cells.
Section 4: GENETIC VARIATION: 2 possibilities, Dependent assortment & Independent Assortment. In
chapter 9, Mendel finds Independent assortment occurs in nature
At Metaphase I arrangement of chromosomes occur. In Possibility I: Dependent is where all the red and all the
blue stay together and separate. Combination a & b have either all red or all blue in their respective daughter
cells. In Possibility II: Independent is where the red and blue do not care or have no bearing on each other; the
red and blue pair up. Combination c & d each have 1blue/red. All four possibilities equally can happen. BUT
MENDEL FOUND INDEPENDENT IS WHAT HAPPENS IN NATURE MORE OFTEN. RANDOM
PAIRING.
Another way to get genetic variation is random mating. What does that mean? You don’t which 1 sperm will
fertilize which 1 egg. 3rd way to have variation: mutations. And last, crossing over in PI.
Section 5: MEIOSIS GOES WRONG. It’s actually Anaphase that goes wrong. Nondisjunction is where
chromosomes fail to separate properly. Two types of nondisjunction: Meiosis I (means Anaphase I improper
separation) = will produce all 4 abnormal gametes = 2 of them have 3 chromosomes (n+1); 2 have 1
chromosome (n-1). If nondisjunction occurs in Meiosis II = 2 abnormal = 1 (n+1); 1 (n-1); and 2 normal (n).
If you have trisomy number 21 chromosome = Down syndrome. Look at the karyotype.