The Cell Cycle and
Meiosis
Cell cycle-process by which somatic cells make more of themselves ( reproduce)
Makes exact copies, called daughter cells
3 parts: Interphase-G1( rapid growth, occupies most of the life of a cell), S( DNA
is copied), G2( Final growth)
Mitosis- prophase (4), metaphase( 2), anaphase(1), telophase ( 3)
THE DIVISION OF THE NUCLEUS!!!!!!!
Cytokinesis- division of the cytoplasm and the organelles
3 checkpoints-G1,G2,metaphase
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Vocabulary to know:
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Chromatin-DNA in a “beads on a string” form during interphase
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Chromosome- a visible form of DNA
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Chromatid- half of a chromosome
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Histone-a protein used to allow DNA to wrap around it so it doesn’t get kinked
up, kinda like on a yoyo
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Centromere- a region on a chromosome that holds the sister chromatids
together
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Centriole-an organelle that helps to form the spindle fibers
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Prokaryote, Eukaryote, Parts of the Cell Theory ( old stuff you best know!!!)
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The DNA(genetic material) in a eukaryotic cell during interphase is in a form
called chromatin. Looks like “beads on a string” that wraps around itself. This
allows it to fit inside the nuclear membrane
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The DNA in a bacterium(singular) or bacteria( plural) is in a circular form, like
twisting a rubber band on itself many times
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Normal cells become cancer cells when they do not respond to the
checkpoints
Meiosis “Lingo”
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Vocabulary to know:
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Gamete- a reproductive cell
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Zygote- when two different gametes fuse together during fertilization
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Sperm- a male gamete
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Ovum- a female gamete
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Homologous chromosome-chromosomes that are similar in size, shape and
kinds of genes they contain. Each chromosome in a homologous pair comes
from one of the two parents.
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Crossing over- when chromatids exchange genetic material during PROPHASE I
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Independent assortment-the random distribution of homologous chromosomes
during meiosis
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Vocabulary cont:
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Haploid- a cell that has 1 set of chromosomes (n), 23
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Diploid- a cell that has 2 sets of chromosomes ( 2n), 46
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Autosome- chromosomes that DO NOT determine the sex of an individual. In a
human, these are chromosome pairs 1 thru 22
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Sex Chromosome- chromosomes that determine the sex of an individual. In a
human these make-up the 23rd pair
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Gene- a specific area on a chromosome that codes for a trait
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Trait- a genetically determined characteristic ( ex: green eyes, black hair,
etc..
Types of Asexual Reproduction
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Budding- part of the parent organism pinches off and forms a new organism.
Ex; yeast
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Fragmentation- Ex: the fungus that causes athletes foot
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Binary fission- occurs in single cell organisms ( a bacteria) in which one cell
divides into two cells of the same size
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Vegetative reproduction- occurs in plants. New palnts grow from nonreproductive parts like the stem, root, leaves. Ex: potatoes, strawberries
Sexual Reproduction
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Only one type, FERTILIZATION !
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2 parents give genetic material to produce offspring that are genetically
different than their parents. Requires gametes, an egg and a sperm.
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These gametes are produced from germ cells. These are cells specialized for
sexual reproduction.
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All of the other cells in the body are called somatic cells.
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This process occurs in MOST eukaryotic organisms
Comaparing Sexual vs. Asexual
Reproduction
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Asexual
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Advantages:
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Simplest, most primitive
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Most efficient
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Allows for many offspring in a short amount of time
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Requires little energy
Disadvantages:
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Little to no genetic variation in the offspring compared to the parents, therefore
they may be vulnerable to changes in the environment
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Sexual Reporoduction
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Advantages:

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Produces genetically diverse individuals, therefore there will likely be offspring
that could survive a major environmental change.
Disadvantages:
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Requires 2 individuals ( may be difficult to find a mate)
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Requires a lot of energy ( fighting for a mate, traveling long distances,requires
specialized parts, etc)
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Requires specialized cells
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Process is kinda complicated ( ex: all the steps of meiosis)
Human Chromosome Make-up
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Human GAMETES have 22 autosomes ( non sex determining) and 1 sex
chromosome, this makes up the haploid number (n) of 23
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The human ZYGOTE has 44 autosomes and 2 sex chromosomes
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The sex chromosomes are labeled X and Y
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Males have the chromosome make-up of XY, females are XX
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Because males have 2 different forms, they determine the sex of the child.
The female can only give an X but the male can give an X or a Y
Meiosis In Action
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The process of taking a DIPLOID cell thru 2 divisions to form 4 HAPLOID cells
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Goes thru cell division TWICE !
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Steps:
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Interphase
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Prophase I
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Metaphase I
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Anaphase I
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Telophase I
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Prophase II
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Metaphase II
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Anaphase II
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Telophase II
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Cytokinesis
Differences between Mitosis and Meiosis
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Mitosis
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produces 2 genetically identical daughter cells that are diploid
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Only occurs in somatic cells ( for growth, repair, and ASEXUAL reproduction)
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Only has 1 cell division
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Begins with chromosomes
Meiosis
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Produces 4, NON-IDENTICAL daughter cells that are haploid
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Only occurs in reproductive cells and is used for SEXUAL reproduction
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Goes thru 2 cell divisions
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Begins with HOMOLOGOUS CHROMOSOMES . In Prophase I, every chromosome pairs with its
homologue ( an identical chromosome: XX). Now called a tetrad. Parts of these homologues
exchange pieces of their chromatids with each other in a process called CROSSING OVER.
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When the homologous chromosomes line up in Metaphase I, they do so randomly, this is called
INDEPENDENT ASSORTMENT.
Summary
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Mitosis produces 2 identical diploid cells in somatic cells. Efficient, very simple,
little energy required. Mostly occurs in single-celled organisms( prokaryotes). No (
or very little) genetic variation. Only requires one organism. For repair,
growth/development and asexual reproduction.
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Meiosis produces 4 non-identical haploid cells. Only with reproductive (germ)
cells. Occurs in most eukaryotic cells. For creating cells for sexual reproduction.
LOTS of genetic variation!!!!! 3 main things that lead to this variation:
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Crossing-over
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Independent assortment ( each of the 23 pairs of chromosomes separate independently,
thus 223 gametes( 8 million) with different gene combo’s can be made from one original
cell
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Random fertilization ( to show how much variation, in humans the possibility is 223 x 2223
( 64 trillion ) different combinations !!!!!!!!!