ASEXUAL REPRODUCTION

Euglena

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

TWO TYPES OF REPRODUCTION

1. Asexual 2. Sexual

Coral releases spermatozoa

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?

Mutations

What are identical offspring from a single parent

referred to as?

A clone 

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

FISSION CAN BE:

Binary fission

Paramecium

Amoeba

Multiple fission

Plasmodium

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 PLANTAE

at some stage the new plant becomes detached and leads an independent life

KINGDOM PLANTAE

specialised organs of propagation often develop, but they must all have buds

EXAMPLES ARE BULBS, CORMS, RHIZOMES, RUNNERS AND TUBERS

CORMS IN GLADIOLUS

BULBS IN DAFFODILS & TULIPS

RHIZOMES IN IRIS

RUNNERS IN STRAWBERRIES

KINGDOM ANIMALIA

asexual reproduction occurs only in relatively unspecialised animals

Budding occurs in Cnidaria

KINGDOM ANIMALIA

Budding occurs in Cnidaria – outgrowth of organism that may detach

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

KINGDOM: ANIMALIA Fragmentation:

- ribbon worms

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.

THE END