The Continuity of Life
Reproduction
Reproduction
Sexual
Reproduction
Asexual
Reproduction
SEXUAL REPRODUCTION
 In sexual reproduction, genetic information from two cells combines
to produce a new organism.
 Usually, two specialized sex cells unite in sexual reproduction and they
form a fertilized egg called a ZYGOTE.
 Zygote contains a mixture of the two parent organisms genetics.
Sexual reproduction advantages
• Genetic variation
• Offspring are dispersed widely to end up in different places
from their parents.
Sexual reproduction disadvantages
• Need two parents “must expend energy” to find, identify
(court), and copulate with mate
• Only half the individuals are producing offspring-(Males are
an energy issue)
• Less efficient at passing on genes as their may be mistakes in
the copying process of DNA
Types of Sexual Reproduction
 Hermaphrodism: both sexes occur in the same organism
 Some self-fertilize, others, cross-fertilize
 These organisms have both male and female reproductive
organs, and are said to be monoecious, meaning “one house.”
 Almost 70% of plants! And earthworms..
Types of Sexual Reproduction
 Sequential Hermaphrodism or Sex switching: individual
changes sex during life. Usually male and then female.
 Reversal often associated with weight and size
Female
Male
Asexual Reproduction
ASEXUAL REPRODUCTION



Asexual disadvantages
 No recombination of genes
 An asexual population tends to be
genetically static
Asexual advantages
 Need one individual to reproduce; can conserve energy
 No genetic change “good” if environment is stable
 All individuals are producing offspring
 More efficient passing genes, “faster”
Definition
Sexual
Reproduction
Asexual
Reproduction
•Involves sex cells and
fertilisation
•Does not involve sex
cells and fertilisation
•Only one parent plant
Advantages/
Disadvantages
•Offspring are not
genetically identical to
one another
•There is variation in
the offspring
•Offspring have no
variation
•Offspring are
genetically identical to
one another
Sexual vs. Asexual
Some organisms are capable of both sexual & asexual
common in plant kingdom!!
WHY???
Asexual
• produces identical copy (clone) relatively fast
• Easiest means of reproduction
Sexual
• requires more energy & time than asexual
• produces genetic variation
Sexual vs. Asexual
When environment is not changing…
Asexual will allow well-adapted organisms to rapidly reproduce
When environment is ever changing…
Asexual will have difficulty adapting
Sexual allows species shows variance between generations,
which will have a better chance of survival
Imagine…
 Imagine that a particular organism within a species lacks a
certain gene (or ability to express a certain gene) necessary
to break down a specific type of food, yet others of the same
species within the population are able to break down that
food.
 What happens if the uncertain or less favorable
conditions lead to that being the primary food source?
Death…
 The parent organism and all of their offspring produced
would die!
 But, with the genetic diversity that comes from sexual
reproduction the possibility of the offspring surviving is
enhanced.
Methods of asexual
reproduction
Binary Fission – ex. Amoeba
Budding – ex. yeast
Fragmentation – ex. Sea Star
Vegetative Propagation – ex. Kalanchoe
Spores – ex. Ferns
Types of Asexual Reproduction
 Unicellular:
Fission-splitting
into two
organisms
from one
BINARY
FISSION
 An organism simply splits
into equal sized offspring.
 + Fast and easy
 - Everybody has the same
DNA
Budding…
 New Organisms Arise as
an Outgrowth from the
Parent Organism
 Seen Mostly in Marine
Animals
 Examples Include; Sponges,
Corals and Jellyfish…
Coral Polyp Photo courtesy Jeffrey N. Jeffords
http://oceanworld.tamu.edu/students/coral/coral1.htm
They Where best buds
 Budding = Parent organism divides into two
unequal parts.
 The new organism is created as a smaller out growth
or bud on the outside of the parent.
 Buds will brake off and live independently or
remain attached and form a colony.
BUDDING
 The offspring begins as
a small outgrowth from
the parent and
eventually breaks off.
 Yeast & hydras
 + Fast, somewhat easy
 - Same DNA
Regeneration…
 This refers to the ability of
some animals to regrow severed parts.
 Some of these animals can
also grow new organisms
from the severed pieces
(Segmented Worms and
Sea Stars)
Don’t try this at home
 Regeneration = The ability to re-grow lost or
damaged body parts. Hydra, planaria, starfish, and
earthworm More complex animals less able to regrow parts. Crab can re-grow a claw. Some reptiles
can re-grow a tail. Most mammals can repair
damaged tissue but can not re-grow missing parts.
FRAGMENTATION
 A new organism
forms from a part
that breaks off from
the parent.
 Fungi & sea stars
 + Easy
 - Parent broken, same
DNA
FRAGMENTATION
Moss
Parthenogenesis…
 Offspring can arise from
unfertilized eggs.
 Includes some Fish,
Reptiles, Amphibians and
Aphids.
 Most of these species can
switch between Sexual and
Asexual Reproduction.
http://aolsearch.aol.com/aol/imageDetails?invocatio
nType=imageResults&query=photos+of+parthenoge
nic+species&img
http://www.duke.edu/%7Ejsr6/Ha
waiipics/Rhampho.jpg
(depending on conditions)
http://spot.colorado.edu/~noyesr/TEACHING/4800
%20Fall%202002.%20Biology%20and%20Evolution%2
0of%20Sex/Gynogenesis.Poecilia.pdf
www.ag.ndsu.nodak.edu
VIDEO CLIPS
 http://www.youtube.com/watch?v=K0ZP8VtxUZ0 (Binary
Fission)
 http://www.youtube.com/watch?v=l7JYvXPRPlE (Binary
Fission)
 http://www.youtube.com/watch?v=dcNEfUnEt_g (Budding)