asexual reproduction
TRANSCRIPT
REPRODUCTION is the production of a new generation
of individuals of the same species
involves the transmission of genetic material from one generation to the next, ensuring that the species survives over long periods of time, even though individual members die
ASEXUALREPRODUCTION
is reproduction by a single organism without production of gametes
usually results in the production of genetically identical offspring
How can variation occur in asexual reproduction?
ASEXUALREPRODUCTION
most animal species do not naturally reproduce asexually
there are several types of asexual reproduction
SEXUAL REPRODUCTION is the fusion of two gametes to form a
zygote which develops into a new organism
leads to genetic variation
SEXUAL REPRODUCTION
genetic variation is advantageous to a species because it provides the ‘raw material’ for natural selection and hence evolution
offspring showing most adaptations to the environment will have a competitive advantage over other members of the species and be more likely to survive and pass on their genes to the next generation
sexual reproduction occurs in almost all species
KINGDOMS: PROKARYOTAE AND PROTOCTISTA in unicellular organisms, asexual
reproduction occurs by a process called fission
• fission is the division of the cell into two or more daughter cells identical to the parent
- Binary fission
- Multiple fission
FRAGMENTATION is the breaking of the organism into two
or more parts, each of which grows to form a new individual e.g. Spirogyra
KINGDOM PLANTAE
vegetative propagation:
the most common form of asexual reproduction in plants
is a form of asexual reproduction in which a bud grows and develops into a new plant
KINGDOM ANIMALIA
asexual reproduction occurs only in relatively unspecialised animals
Budding occurs in Cnidaria
KINGDOM: ANIMALIA
Fragmentation:
is the breaking of the organism into two or more parts, each of which grows to form a new individual e.g. starfish
QUESTION: MAY, 2011
Use your knowledge of biology to describe the significance of the following.
The waterflea, Daphnia, generally reproduces through parthenogenesis. However, during periods of ecological or abiotic stress, eggs hatch into males, allowing sexual reproduction to occur. (5 marks)
KINGDOM ANIMALIA
Parthenogenesis is a form of asexual reproduction in which females produce eggs that develop without fertilisation
- is virgin birth
PARTHENOGENESIS OCCURS IN :Invertebrates :
Vertebrates :
fish, amphibians, reptiles (whiptail lizard)
1st recorded in sharks in 2007.
aphidsrotifersDaphnia
honey bee
Daphnia reproduces by:
parthenogenesis in Spring to rapidly populate ponds,
switches to sexual reproduction as
intensity of competition and
predation increase
HONEY BEE LAYS: • fertilised eggs = workers or queens• unfertilised eggs = drones (males)
Queen Worker (female) Drone (male)
KINGDOM ANIMALIA
few species reproduce solely by parthenogenesis
possible to induce artificial parthenogenesis even in mammals
pricking frog eggs with a needle resulted in development [first demonstration of parthenogenesis in 1900]
unfertilised eggs can be induced to develop if exposed to:
diluted acids
UV or radium irradiation
temperature changes
Dr Gregory Goodwin Pincus produced rabbits by
parthenogenesis in 1937 by temperature changes.
Parthenogenesis has been induced in:
mice (Tokyo University of Agriculture, 2004), and monkeys
ADVANTAGES OF NATURAL ASEXUAL REPRODUCTION
1) Only one parent is required
• time and energy are wasted in finding a mate for sexual reproduction but not for asexual
2) Genetically identical offspring
• successful combination of genes are preserved
3) Dispersal and spread
• the methods of asexual reproduction often enable dispersal of a species
e.g. spores are light and easily dispersed by air currents
4) Rapid multiplication
•many parasites rely on one or more asexual stages where rapid multiplication compensates for large losses at other stages in the life cycle e.g. malaria parasite, tapeworm, liver fluke
DISADVANTAGES OF NATURAL ASEXUAL REPRODUCTION
1) No genetic variation
2) If spores are produced, many will fail to find a suitable place for germination
3) If an organism spreads in one area, it may result in overcrowding and exhaustion of nutrients
COMPARISON OF ASEXUAL WITH SEXUAL REPRODUCTION
Asexual reproduction Sexual reproductionOne parent only Usually two parentsNo gametes are produced
Gametes are produced
Depends on mitosis Depends on meiosis to prevent chromosome doubling in every generation
Offspring identical to parent
Offspring are not identical to parents
COMPARISON OF ASEXUAL WITH SEXUAL REPRODUCTION
Asexual reproduction Sexual reproductionCommonly occurs in plants, simple animals and microorganisms. Absent in complex animals
Occurs in almost all plant and animal species
Often results in rapid production of large numbers of offspring
Less rapid increase in numbers
QUESTION: MAY, 2009
Use your knowledge of biology to describe the selective advantage of the following adaptation:
Vegetative propagation. (5 marks)
Flowering plants can reproduce sexually by flowers and asexually by vegetative propagation. By vegetative propagation: desirable features of the parent are
inherited. as only one parent is needed, no resources
are wasted in making gametes + a sure way to produce offspring
the number of offspring produced is large and process is quick.
Thus, the species can spread rapidly and make use of the resources available while they last.