Chapter 7: Cellular Reproduction
Cell Cycle and Mitosis
1. All cells in your body came from 1 cell – a fertilized egg
a. All new cells contain cytoplasm, organelles and nucleic acids –
which are needed for the cell to survive and function
b. The orderly processes that occur during cellular division ensure
that cell reproduction is always carried out correctly
2. Phases in the life of a cell are called the cell phase
a. Interphase
b. Prophase
c. Metaphase
d. Anaphase
e. Telophase
3. Interphase
a. Longest phase
b. Used to be called resting phase
i. Actually very busy phase
c. Cells carry out all their usual functions, i.e. respiration, enzyme
production, grow and develop into mature functioning cells
d. G1: number of organelles and the amount of cytoplasm in the cell
increases
e. S: chromosomes replicate
i. Replication is the process of copying genetic material
1. results in 2 identical sets of chromosomes
ii. chromosomes: a condensed bundle of chromatin that
appears during cell division; contains the DNA of the cell
iii. sister chromatids: are identical copies of each
chromosome that result from replication
1. remain attached to each other at a point called a
centromere
2. chromosomes must replicate during Interphase so
that there will be a complete copy of each
chromosome in each new cell
f. G2: cell makes organelles and substances it needs for cell
division
g. Chromosomes too thin and tangled to be seen during interphase
4. Cell division
a. 2 main steps
i. Mitosis: a series of phases in cell division in which the
nucleus of a cell divides into 2 nuclei with identical
genetic material
1. occurs only in eukaryotes
ii. Cytokinesis: during which the cytoplasm of the cell
divides into 2 new cells, called daughter cells
1. each daughter cell receives 1 of 2 nuclei
Mitosis + Cytokinesis + Mitotic Cell Division
2. daughter cell nuclei are identical to the parent cell
nucleus in every way
b. Multicellular organisms grow as more cells repeat the cycle of
cell division and growth
c. In some cells Cytokinesis may not occur at all
i. Some muscle cells repeated mitosis with no Cytokinesis
forming multinucleated cells/fibers
5. Mitotic Cell Division and Cytokinesis
a. Chromosomes are ordinarily transparent and invisible
b. 1880s Walther Fleming found a way to stain nucleus
i. chromosomes mean “colored bodies”
c. Interphase: chromosomes replicate, cytoplasm increases
i. G1, S, G2
d. Prophase: sister chromatids condense and become thicker ( can
be viewed with a microscope); nucleolus and nuclear envelope
disappear; microtubules that make up spindle fibers begin to
assemble
e. Metaphase: chromosomes move to the center of cell by spindle
fibers; attached by centromeres
i. 2 sister chromatids of each chromosome are attach to
spindle fibers radiating from opposite ends of cell
f. Anaphase: centromeres of each chromosome pulled by spindles
toward ends of cell
i. Sister chromatids have been separated
g. Telophase: new nucleus begins to form around the chromosomes
at each end of cell
i. Mitosis now complete
ii. Cell membrane begins to pinch the cell in two as
Cytokinesis begins
h. Cytokinesis: completes the process of cell division
i. During Cytokinesis the cytoplasm of a cell and it’s
organelles separate into 2 daughter cells
ii. Animals: cytoplasm divides when a groove called a
cleavage furrow forms through middle of parent cell
1. Cleavage furrow deepens until parent cell is
pinched “in two”
iii. Plant: material for cell walls and membranes gather and
fuse along the equator or middle of the cell – between
the 2 nuclei
6. Control of Mitosis
a. Cancer: cells begin to divide, grow and change abnormally
i. Tumors and cancer – results in growth and spread of
abnormal cells
ii. Causes: heredity, certain chemicals, radiation etc.
iii. Tumor: abnormal growth
1. Can be benign or malignant
a. Benign: cells remain together, usually cause
little harm
b. Malignant: cells do not remain together; may
break free from the tumor; migrate to new
locations and start new tumors
iv. Cancer: spread of malignant cells to new locations
1. cancer cells can spread freely because they lack
the surface protein that bind normal cells together
2. Cancer was once thought to be disorganized cell
growth
a. Now: cells acquire abnormal size, shape and
abilities to invade normal
b. tissue and replace healthy cells
b. Normal growth and repair
i. Multi-cellular organism grows as its cells produce new
cells by mitosis and new cells grow larger
1. some change to take on specialized shapes and
functions
2. differentiation: changes that take place in cells as
they develop
a. contact between new cell and surroundings
cells help determine what kind of cell the
new cell will become
ii. in most animals, mitosis stimulated by chemicals called
growth factors
1. most are highly specific
2. cause mitosis in only 1 type of cell
3. growth factors are “chemicals that stimulate the
division and differentiation of new cells during
growth ‘
a. also stimulate cell division when new cells
are needed to replace injured ones
b. regeneration: process of growing back lost
body parts
i. some animals can regenerate
ii. cells at site of wound become less
specialized and divide
iii. new cells differentiate to become
bone, muscle, nerve, skin
iii. asexual reproduction: “reproduction in which one parent
produces offspring by cell division”
1. produces new individual that has DNA identical to
DNA of parent
2. common for: bacteria, fungi, plants and some
animals
a. budding: new organism grows from piece of
another organism
i. parent produces offspring by growing
a tiny replica of itself – a bud – on
some part of its body
ii. after enough growth, the bud
separates from the parent and
becomes independent
b. fragmentation: separate pieces of parent
organism can develop into new organisms
i. flatworm can pinch itself :in two” –
each part can develop into a new
organism
ii. sea star – if torn apart, each part
with a piece of the central ring can
develop into a separate individual
c. vegetative reproduction: new plant grows
from stem, root or leaves of an existing
plant
i. contain exact same DNA as original
plant
Meiosis and Sexual Reproduction
1. Sexual reproduction – “when the chromosomes of 2 parent s combine
to produce offspring
a. Gametes - “chrosomes that combine during sexual reproduction
are contained in special reproductive cells called gametes”
i. Female gamete – egg – large, lots of cytoplasm
ii. Male gamete – sperm – small, little cytoplasm, flagella
b. Chromosomes of 2 gametes join
i. Chrosomes number in parent and zygote must match
2. Meiosis; production of gametes
a. A type of cellular reproduction
b. Occurs only in eukaryotes
c. Differs from Mitosis:
i. Produces daughter cells that have ½ the number of
chromosomes of parent cell
ii. Daughter cells not all alike due to the way cell divides
during meiosis – the cells may have different
chromosomes from each other
iii. Number of cells produced is different
1. in mitosis – 1 parent cell produces 2 daughter cells
2. in meiosis – 1 parent cell produces 4 daughter cells
d. chromosome number – every gamete contains 1 complete set of
chromosomes
i. considered complete because together the chromosomes
contain all the information needed for organism to
function properly
ii. in humans – each gamete has 23 chromosomes
1. all other body cells have 46 chromosomes
iii. diploid: any cell that contains 2 complete sets of
chromosomes – 1 donates by “mom” and 1 donated by
“dad”
iv. number of chromosomes in diploid cell is called the
diploid number
1. represented by the notation 2N
2. every organism has characteristic diploid organism
has characteristic diploid number
a. not related to its complexity or size
v. haploid: a cell with only 1 complete set of chromosomes
1. represented by the notation N
e. Fertilization – when an egg cell and a sperm cell of the same
type of organism join to produce a new individual
i. Zygote – single cell that results from fertilization
1. contains 2 complete sets of chromosomes
2. chromosomes exist is pairs – 1 from each gamete
3. Homologous pairs – matching pairs of chromosomes
in a diploid cell
4. both chromosomes in a homologous pair code for
the same traits
3. Phases of Meiosis
a. Meiosis – number of chromosomes in each cell is reduced from
diploid to haploid by separating homologous pairs of
chromosomes
b. 2 main stages
i. Meiosis I – homologous pairs separate
ii. Meiosis II – sister chromatids of each chromosome are
separated
c. Meiosis I – at the start: each chromosome consists of 2 strands
of sister chromatids connected by a centromere
i. Prophase I
1. chromosomes become thick and visible
2. chromosomes of each homologous pair become
tangled
3. each pair consists of 4 chromatids – because each
chromosome in the pair has replicated before
meiosis began
4. by the end of prophase I, nucleoli and nuclear
envelope have disappeared
5. spindle fibers are forming
ii. Metaphase I
1. homologous chromosomes are still together
2. pairs of chromosomes are arranged in the middle
of the cell
iii. Anaphase I
1. homologous pairs separate from each other
2. spindle fibers pull 1 member from each pair to
opposite ends of the cell
3. each chromosome still consists of 2 sister
chromatids
iv. Telophase I
1. new nuclear envelope may or may not form
2. Cytokinesis does occur; each new cell is haploid –
containing 1 chromosomes from each pair
d. Meiosis 2
i. Chromosomes do not replicate before beginning second
division
ii. Sister chromatids remained attached during 1st meiotic
division
iii. Each daughter cell produced during meiosis I divides
again during meiosis II
1. sister chromatids of each chromosome separate
and are divided between 2 new cells
2. remember, during mitosis sister chromatids are
also divided between 2 cells
iv. in animals Mitosis divides chromosomes in a diploid cell;
meiosis II divides the chromosomes in a haploid cell
e. crossing over –
i. gene: code for 1 trait or characteristic of the organism
ii. chromosomes contain/carry many genes
iii. crossing over: the exchange of genes between pairs of
homologous chromosomes
iv. usually occurs during prophase I of meiosis when
homologous pairs are still joined
1. homologous chromosomes break and exchange
genes
2. after crossing over, each chromosome in the
homologous pair has a different combination of
genes than it had before meiosis began
4. Meiosis and Evolution
a. Meiosis results in new combinations of characteristics with a
population
b. Evolution is the process of change in living populations over time
c. Variation – differences among members of a population are
collectively called variations
i. Result from recombination of genes during meiosis and
fertilization
ii. Random separation of homologous pairs of chromosomes
produce new combinations of genes
d. Organisms characteristics enable it to survive in its
environment
i. Not all characteristics are equally “well suited”
ii. Conditions of environments determine the traits that
benefit the survival of an organism and which do not
iii. As environments change, traits that were once beneficial
could become a disadvantage
e. Genetic variation rarely occurs from generation to generation
among asexual organisms
i. Change in environment could destroy entire population
f. Reshuffling of genes that occur during meiosis ensures a
certain amount of genetic variation in a population
i. Variety of traits within the population increase the
chance that some individuals will survive the change