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Cell Reproduction
Chapter 8
Chromosomes
Section 8.1
Definitions:
Chromosome: rod shaped structure made
up of DNA and proteins
Sister Chromatids: identical halves of a
chromosomes
Definitions:
Centromere: protein that holds sister
chromatids together
Homologous Chromosomes:
chromosomes that code for the same traits
that come from your mother and your
father
Definitions:
Chromatin: less tightly coiled strands of
DNA
Uncoiled so that the cell can read the DNA to
direct the cell’s activities
Chromosomes only occur during cell
division
Chromatin coils up to make chromosomes
Ameba
50 Goldfish
94
Alligator
32
Garden Pea
14
Brown bat
44
Grasshopper
24
Bullfrog
26
Horse
Human
46
Cat
32
Lettuce
18
Chicken
78
Onion
16
Chimpanzee
48
Redwood
22
Corn
Earthworm
36
Fruit fly
64 Carrot
18
20
8
Sand dollar
52
All normal
members of
the same
species have
the same
number of
chromosomes
in their body
cells.
Sex Chromosomes
Definition: chromosomes that determine
the sex of the organism
May carry other genes as well
Humans: X and Y
Males: XY
Females: XX
Autosomes:
Definition: All other chromosomes in the
body besides the sex chromosomes
Humans = 46 total chromosomes
2 sex chromosomes
44 autosomes
Karyotype – map of an organism’s
chromosomes
http://www.chromosome18.org/AboutGene
tics/BasicGenetics/WhatisaKaryotype/tabi
d/120/Default.aspx
Karyotype – map of a organism’s
chromosomes
Diploid and Haploid Cells
 Cells having 2 sets of
chromosomes are diploid
(2N)
 The haploid number of a
human egg or sperm cell is
23, and there are no
homologous chromosomes
in either cell (1N)
Mitosis
Section 8.2
Why Cells Divide
 Cell size is limited
Cells cannot keep
growing indefinitely
 Replacement of
damaged cells
 Growth - embryo
 Asexual reproduction
Single celled life forms
Binary fission
 Sexual reproduction meiosis
Eukaryotic Cell Division
Mitosis (Growth Division): Division of cell
producing two identical daughter cells
2n  2n
Meiosis (Reduction Division): Division of
cell producing four haploid daughter cells
2n  1n
The Cell Cycle (Life Cycle of the Cell)
2 Major Parts:
1. Interphase
G1
S
G2
2. Cell Division
Mitosis –
nucleus
Cytokinesis –
cytoplasm
Part 1: Interphase
 Stage your cells are
in the most amount of
time
 When cell does its
“normal” jobs
 Contains 3 stages:
G1, S, and G2
G1 Phase
cell doubles in size
enzymes and ribosomes
and mitochondria
double in number
cell growth
S Phase
Cytokinesis
Mitosis
DNA replicates
Growth and preparation
for mitosis
G2 Phase
rapid growth,
synthesizing necessary
enzymes and structures
for mitosis
S Phase – DNA Replication
 Process by which DNA
builds an exact copy of
itself
 After replication has
occurred, each double
stranded molecule
contains one old strand
and one new strand of
DNA
1879 Walter Flemming used red dye to
observe cell structures during mitosis, it
killed the cells and so he had to take
pictures at each stage in order to come up
with a pictorial model of mitosis.
Part 2: The Stages of Mitosis
(page 156)
Mitosis – Step 1: Prophase
Chromosomes (2 chromatids) form from
chromatin
Nuclear membrane disassembles
Centrioles move to poles
Spindle fibers form
Mitosis – Step 2: Metaphase
Chromosomes line up at the middle of the cell
“Metaphase Plate”
- Stage
where karyotypes are made from!
Mitosis – Step 3: Anaphase
Sister chromatids (from the same
chromosome) separate and move to
opposite poles
Mitosis – Step 4: Telophase
Spindle fibers disappear
Nuclear membrane forms again
Chromosomes go back into chromatin
form
2 nuclei (diploid) per one cell
Cytokinesis
Division of cytoplasm
Cell membrane pinches in to form two
separate cells
Results: 2 IDENTICAL daughter cells
Animation
 Mitosis
Mitosis “Flip Book”
 To receive full credit you must:
1. Illustrate what is going on in the life cycle
a) Title Page
b) Interphase: G1, S, G2
b) Mitosis: prophase, metaphase, anaphase,
telophase
c) Cytokinesis: early & late
d) Finished product
2. Diploid # (2N) = 8
Haploid # (1N) = 4
(represent homologous chromosomes with different
colors)
Need help? Consult your book or your notes!
Cont…
3. Diploid # (2n) = 8
Haploid # (1n) = 4
4. Represent homologous pairs with 4
different colors.
Need Help? Consult you book or your notes!
Asexual Reproduction
offspring is an exact copy of parents occurs in lower plants and animals
(bacteria, molds, algae and protozoa)
all cells form through mitosis
Asexual Reproduction
Regeneration
Budding
Spores
Binary Fission
Mitosis Slides
Meiosis
Section 8.3
2 Stages:
2n
Meiosis I
n
n
Meiosis II
Results in 4 haploid cells
n
n
n
n
Interphase
Same as mitosis!
3 Stages: G1, S, G2
Meiosis I
Formation of 2 haploid cells from 1 diploid
cell
Production of gametes
“Reduction division”
Step 1: Prophase I
•Nuclear membrane breaks
down
•Centrioles move to the poles,
spindle fibers form
•Synapsis occurs, forming
tetrads, allowing for crossing
over (genetic variety)
Definitions:
Synapsis: When a pair of homologous
chromosomes partner up inside a dividing cell
Tetrads: the name given to a partner of
homologous chromosomes during synapsis
Crossing over: chromatids of homologous
chromosomes twist around and trade places
causing an exchange of DNA
Step 2: Metaphase I
Tetrads line up randomly at the
metaphase plate
Step 3: Anaphase I
Tetrads are split and each
homologue is moved toward opposite
poles
Independent assortment: the random
separation of maternal and paternal
chromosomes
Resulting in genetic variety of offspring
Step 4: Telophase I
Nuclear membrane reforms
Spindle fibers and centrioles disappear
2 nuclei per cell
Each nucleus now has HAPLOID number
of chromosomes
2n  1n
Cytokinesis I
Splitting of the cytoplasm to produce 2
haploid daughter cells
Meiosis II
•NO interphase between meiosis I
and II
•The production of 4 haploid cells
from 2 haploid cells.
•EXACT same process as
mitosis!
Step 1: Prophase II
Step 2: Metaphase II
Step 3: Anaphase II
Step 4: Telophase II
Cytokinesis II
 End result = 4 haploid cells
Purpose: Gamete Production
Gamete: sex cells (egg & sperm)
Oogenesis – egg production
Spermatogenesis – sperm production
Sexual Reproduction: genetic diversity of
offspring
Page 155
Sexual Reproduction
Each parent contributes genes to the
offspring.
 each offspring has a different set of
inherited traits from the parents
gives offspring a better chance of surviving
in a changing environment
Mitosis vs Meiosis
 Mitosis
1 division
2 daughter cells
Exact copies of parent cells
Diploid to diploid
Purpose
 Growth
 Repair
 Asexual reproduction
 Meiosis
2 divisions
4 daughter cells
Each unique
Diploid to haploid
Purpose
 Make gametes/ sex
cells
 Leads to genetic
variation
Cancer
Cell cycle control system
Enzymes in cell control when and where cells
divide
Malfunction in system means cells divide
at inappropriate times and places
Benign tumor - abnormal mass of essentially
normal cells
Stay at original site, don’t move
Cancer uncontrolled cell division
Cancer
 Problem not only uncontrolled division
 Metastisis
Cancer cells can move to other sites
New tumor at that site
 Three treatments
Surgery to remove tumor
Radiation
Chemotherapy
Last two aimed at controlling division
Cancer treatments
 Radiation
Disrupts cell division
Most actively dividing cells are tumor
Can damage normal cells- ovaries / testes
 Chemotherapy
Some disrupt cell division
Taxol freezes spindle
Vinblastine prevents spindle formation
 Cancer cells immortal in cell culture
Normal cells stop growing after 50 culture