Cell Reproduction Power Notes
2 Types of Reproduction:
1.Asexual-single parent gives rise to one or more individuals (binary fission,budding, fragmentation).
2.Sexual-the joining of 2 specialized sex cells (sperm and egg), usually from different parents.
Asexual Reproduction
Binary Fission: becoming 2 by
division of the complete organism.
Budding: new plant or animal
begins to form at the side of the
parent.
Fragmentation: new organism
form from severed body part.
MITOSIS
1.Occurs in body cells (somatic); these are all the cells in the body except sex cells ( egg and sperm).
2.Parent cell divides to form 2 daughter cells with the same number of chromosomes as parent cell.
3.Mitosis occurs to provide cells for growth, healing, and replacement of body parts (regeneration).
Homologous Chromosomes:
pairs of chromosomes.
Diploid number (2N): total
number of chromosomes in
the cell.
Chromosomes: 2 sister chromatids
joined together by a centromere.
Mitotic Spindle: spindle fiber forms
between the centrioles during cell
division.
Cell Cycle-IN ORDER
Fibers are used to pull the chromatids
apart during Anaphase.
2.Prophase
1. Interphase
3.Metaphase
4.Anaphase
Cen
5.Telophase
How many chromosomes do humans have? 46 Pairs? 23
Interphase:
1.Cell grows
2.Nucleolus and chromatin are visible.
3.Centrioles are visible outside nucleus in animal cells.
4.Chromosomes are duplicated.
After replication in humans, there are 92 chromsomes.
Pairs? 46
The 23rd pair is called sex chromosomes.
XX- Girl
XY-Boy
Chromosomes 1-22 are called autosomes.
Prophase
STAGES OF MITOSIS
Metaphase
Anaphase
1.Chromosomes are visi
ble.
1.Chromosomes line up
at equator.
1. Centrioles divide.
2.Nuclear membrane and
nucleous fall apart.
2.Centromeres are
attached to the spindle
fibers.
2.Chromatids separate
and move centromeres
first towards the poles
of the cell.
3.Centrioles are now at
the poles of the cell.
3.Cleavage furrow
forms.
3.Centrioles begin to
migrate to the poles of the
cell.
4.Spindles form.
5.Asters appear.
In animal cells, the cytoplasm divides along equator
until two daughter cells are formed; this splitting of
the cytoplasm is called cytokinesis.
In plant cells, a cell plate forms in the middle of the
spindle.
New daughter cells will enter into interphase to begin
the cycle over again.
Telophase
1. Chromosomes become
threadlike again.
2.Spindle breaks apart.
3.Nucleolus reappears.
4.Nuclear membrane forms
around the chromatin mass.
5.Centrioles replicate.
Meiosis: Formation on sex cells
1. Cell division which results in the formation of gametes, also known as sex cells (egg and sperm).
2.Occurs in reproductive organs
Females- ovaries
Males- testes
3.Gametes are ova (eggs) in females and sperm in males.
4.The chromosome number is reduced to one half (from 2n to 1n) and gametes are formed.
5.Cell undergoes 2 divisions, but the chromosomes are duplicated only once. This means that the 46 chromosomes
have duplicated to 92, and then after two divisions, produces cells with 23 chromosomes.
6.The two divisions result in a total of 4 daughter cells, each having one half the number of chromosomes as the parent
cell. Again, this is called the 1n, or haploid number.
7.Unlike some somatic cells( contain 46 chromosomes), each sex cell contains 23 chromosomes.
8.when fertilization occurs, the zygote will have 46 chromsomes.
• Egg(23) + Sperm(23)  Zygote(46)
9.If a gamete contained the 2n number of chromosomes, fertilization would result in a zygote with twice the diploid
number (92 chromosomes), and it would not be viable.
Fertilization: the union of egg and sperm.
Spermatogenesis: Process in males that occurs in the testes and
produces 4 viable sperm cells.
Zygote: produced as a result of fertilization.
Oogenesis: Process in females that occurs in the ovaries and
produces 1 viable 3gg and 3 polar bodies.
Meiosis has 2 divisions:
1. Meiosis I
2.Meiosis II
Prophase I, Meiosis I
1. Chromatin shortens and thickens.
2.Chromosomes are visible as two chromatids joined by a centromere.
3.Nuclear membrane and nucleolus break apart.
4.Spindle fibers form.
5.Synapsis- homologous chromosomes line up (pair up) beside each
other and become closely entwined.
6.Each of the chromosome is made up of 2 chromatids; therefore, the
pair of chromosomes is made of 4 chromatids. These 4 chromatids make
up a tetrad.
7.During synapsis, the chromosomes twist around one another;
sometimes they break and exchange genetic information This is called
crossing over. This gives us genetic variations in families.
Why is crossing over important?
It allows variation in the produced
offspring as genes from both
parents are present in the
organism.
Offspring may have certain traits
from each parent.
Metaphase I, Meiosis I
Anaphase I, Meiosis I
1. Tetrads line up along
equator.
1. Homologous
chromosomes (tetrads)
separate with one
chromosome of each pair
moving to each pole.
2.Homologs are paired
along equator.
3.Each chromosome is
attached to a spindle
fiber.
2.Cleavage furrow is
occurring.
3.Individual chromatids do
NOT separate at this time.
Prophase II, Meiosis II
Telophase I, Meiosis I
1. Cytoplasm divides
forming 2 daughter
cells (cytokinesis).
2.Nuclear membrane
forms around the
chromosomes in each
cell.
3.Each cell contains
the diploid number of
chromosomes.
Metaphase II, Meiosis II
1. Nuclear membrane and nucleolus
break apart.
1. Chromosomes line up at the
equator.
2. Chromosomes shorten and become
visible.
2. Each chromosome is attached
to a spindle fiber.
3. Spindle fibers forms.
Telophase II, Meiosis II
1. Cytoplasm splits (cytokinesis).
2.Two daughter cells are formed
from each parent cell having the
haploid number of chromosomes.
This results in 4 daughter cells each
1n.
3.The nuclear membrane reappears.
Following Telophase I of
Meiosis I, the two
daughter dells enter into a
phase called Interkinesis.
This is similar to
Interphase, but the
chromosomes do NOT
replicate.
Anaphase II, Meiosis II
1. Centromere divides.
2. Chromatids separate and move
centromere end first toward the
poles of the cell.