Download Asexual Reproduction

Asexual Reproduction
With an introduction to:
The Cell Cycle
&
Mitosis
Asexual Reproduction
What is Asexual Reproduction?
•All living things need to reproduce themselves to continue
their species; they do this sexually, asexually, or use a
combination of both
•Asexual reproduction is the opposite of sexual reproduction in
that it does not involve the fusion of both male and female
gametes (sex cells)
•Asexual reproduction means (1) that an individual, or part of
an individual can produce an offspring that has identical
genetic makeup to itself, or (2) grow or regenerate new tissue
that also is genetically identical
• An identical offspring is known as a clone.
•Uses a process called Mitosis to produce new cells
Asexual Reproduction
In comparison to sexual reproduction….
Advantages
Disadvantages
•Organism doesn’t need to invest
time and energy in a partner
•No opportunity for genetic
variation by mixing of genes
•Organism doesn’t have to travel
to propagate its species
•Little genetic change within a
species gene pool means little
chance of species improvement
and evolution
•Less chance of harmful genetic
mutation
•Less chance of anything going
wrong as it is a simpler process
•Maintains desirable traits
•Organisms can reproduce faster
•Lack of genetic change is
particularly harmful to species
when environmental conditions
change and the organism can’t
adapt
Asexual Reproduction
Types of asexual reproduction are:
•Budding
•Fission
•Spore formation
•Fragmentation
•Vegetative reproduction
•Parthenogenesis
Asexual Reproduction
Budding
•This occurs when a new
organism is formed from an
outgrowth from the original
parent
Budding
scar
•When the outgrowth is
large enough it frees itself
from the parent
•Examples include; yeast
cells and some types of
worms
Yeast cell in
the process
of budding
Asexual Reproduction
•Occurs in bacteria and some
protista
•The cell duplicates its DNA
and then extends its cell
membrane from the centre
•The cell elongates from the
centre in each direction until
it is long enough to cleave
•This is a very fast method of
reproduction with the
population of a colony
sometimes doubling every
15-20 minutes.
Binary Fission
Asexual Reproduction
Imagine this one bacteria doubling
every 15 minutes
Binary Fission
How long will it
take to fill this
rectangle?
Asexual Reproduction
Spore Formation
•Spores are single cells
produced by an organism
and released into the
environment to propagate
•Organisms that produce
spores include prokaryotes,
protists, fungi and plants
such as ferns and mosses
A cloud of spores being released
Asexual Reproduction
•Takes place in plants
and animals
•Occurs when the
organism breaks into
2 or more pieces
•A whole new
organism is produced
from each piece
•Examples include;
sponges and some
types of worms
Fragmentation
Asexual Reproduction
•Happens only in plants
•Occurs when a new plant is
produced from part of another plant
•Examples include:
•grafts – used commercially to
produce desirable traits in flowers
and fruit trees
•bulbs – such a daffodils, garlic
•tubers – such as potatoes; new
plants can grow from the tuber
•runners – such as strawberries;
new roots grow from a runner to
make a new plant
Vegetative Reproduction
Asexual Reproduction
•When an individual is
produced from an unfertilized
egg, therefore known as the
virgin birth
•Mostly occurs in invertebrates
•Examples includes bees; the
queen lays eggs that will
produce females if fertilized
and males, or drones, if not
fertilized
Parthenogenisis
Asexual Reproduction
Some background information…………..
•Before we can understand how organisms actually
reproduce themselves asexually at a cellular level, we
need a little background knowledge:
•(1) We need to understand the regular cycles that cells
make within their life cycle – This is known as the cell
cycle
•(2) We need to have a look at the actual process of
nuclear division – This is called mitosis
1. The Cell Cycle
•Most cells replicate
themselves over and over.
Each complete replication is
known as the cell cycle
Finish
•The length of time the cell
cycle takes depends on the
type of cell, but it can vary
from hours to days
•The best way to study the
cell cycle is to think of it as a
24hr clock
•There are 2 main stages……
Start
1. The Cell Cycle
Mitosis
Interphase
G1
G2
S
Phase
•The cell cycle can be
divided into 2 main
parts Interphase and
Mitosis
•Interphase can be
divided into 3 main
sections; G1, S
phase and G2
• Let’s have a closer
look at what happens
during the Interphase
part of the cell
cycle……..
1. The Cell Cycle
•In G1 – or Gap 1 – the cell
grows in size. Chromosome
number is haploid, written as
1N
•In S Phases – or synthesis
phase – the DNA in the
nucleus replicates or
duplicates itself and becomes
diploid, written as 2N
•In G2 – or Gap 2 – the cell
gets ready for cell division
Mitosis
G1
G2
S Phase
1. The Cell Cycle
Mitosis
Interphase
•The Mitosis
section of the cell
cycle can also be
divided up into a
few sections, this
time into 4
sections ……………
1. The Cell Cycle
Telophase
Mitosis:
Anaphase
Metaphase
Prophase
•A mnemonic is useful in
remembering the order of the
stages of mitosis. If you can’t think
of your own try: (He) probably met
Ana (at the) telethon!
Nuclear division
Cytokinesis:
Division of
the
cytoplasm
2. Mitosis
•Mitosis is the division of the genetic material in the
nucleus of the cell
•Each parent cell gives rise, or produces, two identical
daughter cells
•Mitosis has 4 major stages: prophase, metaphase,
anaphase and telophase
•When the nucleus in a cell is not undergoing mitosis it
is said to be in interphase
•Mitosis occurs in all the somatic cells (or body cells)
and not in the gametes (or sex cells) in humans
2. Mitosis
centrioles
A simplified cell
•Mitosis occurs
in the nucleus
of cells
nucleolus
nucleus
nuclear
membrane
cell membrane
Cell
membrane
2. Mitosis
Interphase
•The cell has
replicated its DNA in
S Phase and is now
in G2 Phase
preparing for Mitosis
•The DNA condenses
by folding on itself
even more than
usual
Nuclear
membrane
DNA
•You can start to see
the chromosomes,
they look like
spaghetti on a plate!
one blue
chromosome
from mum
2. Mitosis
Early prophase
•The 6 chromosomes in
this nucleus have been
colour coded in their
homologous pairs so we
can follow them in this
display; 2xblue,
2xgreen and 2xred
one blue
chromosome
from dad
•The coloured pairs are
also called homologous
chromosomes; one
shade is from mum and
one shade is from dad
sister
chromatids
centromere
2. Mitosis
from
mum
Prophase
•The chromosomes
have condensed as
much as they can;
they now look like the
letter ‘H’.
•The two vertical
arms of the
chromosome are
called sister
chromatids and they
are connected by a
centromere
Homologous
chromosomes
from dad
•The centrioles
duplicate themselves
2. Mitosis
Prophase
•The chromosomes
start to line up on
the metaphases
plate that runs
down the centre of
the cell
•The centrioles
start to move in
opposite directions
•The nuclear
membrane begins
to break down
metaphase
plate
2. Mitosis
Late Prophase
•Centrioles
continue to
move to
opposite ends of
the cell
•Nuclear
membrane
breaks down
even more
2. Mitosis
Late Prophase
•Centrioles arrive
at opposite ends
of the cell
•Nuclear
membrane has
completely broken
down
2. Mitosis
Metaphase
•Chromosomes
are lined up on
the metaphase
plate
•Centrioles
build spindle
fibres
•Centromeres
join to spindle
fibres
Spindle
fibres
2. Mitosis
Anaphase
•Chromosomes
are pulled apart
and sister
chromatids move
to opposite ends
of the cell along
the spindle fibres
2. Mitosis
Anaphase
•Sister
chromatids
continue to
pull part
•Cell
membrane
starts to
pinch or
cleave
cleavage
2. Mitosis
cell plate forms
in plant cells
Telophase
•Cleavage
continues and a
cell plate is formed
in plants cells
only(this becomes
the cell wall)
•New nuclear
membranes form
around the new
nuclei
•Two daughter
cells are now
evident
2. Mitosis
Telophase
•Chromosomes
start to decondense
•Nuclear
membranes
properly
formed
2. Mitosis
Interphase
•The nucleolus
returns
•Chromosomes
are no longer
visible
•Two new
daughter cells
identical to their
parent
2. Mitosis
•So nuclear division, or Mitosis starts from
an interphase cell coming out of G2 and
finishes as an interphase cell ready for G1.
•Let’s have a look again at the process of
Mitosis, this time we won’t
stop…………..(click as fast as you like to work
the animation!)………..
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
Mitosis
The end