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Cell
division and reproduction 7.
Comparing sexual and asexual
reproduction - examples explained in terms of their advantages or disadvantages
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(7) Comparing sexual
and asexual reproduction
Sexual reproduction involves two
parents e.g. human reproduction described above.
Cells of the offspring
produced by asexual reproduction are produced by
mitosis from the parental
cells, but there is only one parent!
In other words the parent cell
makes a new cell by dividing in two.
There is NO fusion of gametes,
so NO mixing of chromosomes, so NO genetic variation
from parents to offspring.
So, in
asexual reproduction the offspring contain the same alleles as the parents,
so they are genetically identical.
Therefore asexual reproduction
produces clones.
Some plants reproduce by
mitosis, so all new plants have identical genes and so are identical plants.
Bacteria reproduce asexually (and
fast, to our cost at times!) and some simple animal organisms like
amoeba which like to live in warm lakes and rivers.
Many fungi like moulds reproduce
asexually much of the time, but can reproduce sexually if they meet a
different strain.
Flowering plants
Flowering plants can reproduce by
sexual reproduction.
Such plants have female egg cells called
ovules,
but they interact with pollen - the equivalent of male sperm.
Pollination is the transfer of pollen
from a male part of a plant to a female part of a plant, so enabling
fertilisation and the production of seeds, most often by an animal (e.g.
insects like bees) or by blown onto a plant by wind.
See
sexual reproduction of
flowering plants.
Comparison of asexual reproduction and sexual reproduction
Their
advantages and
disadvantages
Obviously, reproduction is important for
all organisms to pass on their genes and maintain the species line.
We reproduce sexually as do most other
animals and many plants.
Some organisms e.g. some species of
plant, use asexual reproduction by mitosis.
Some organisms can reproduce both sexually and
asexually depending on conditions.
Cells that
reproduce asexually, divide
by
mitosis
to give two diploid daughter cells which are genetically identical to
each other and their parent cell.
Sexual reproduction involves cell division by
meiosis
and the production of genetically different haploid gametes which
fuse together to form a diploid zygote cell after fertilisation.
| |
ASEXUAL REPRODUCTION |
SEXUAL REPRODUCTION |
|
Parental
genes |
One parent,
genetically identical diploid daughter cells formed by mitosis -
giving limited variations in genes. Bacteria reproduce by binary
fission. |
Two parents,
genetically non-identical daughter haploid cells formed by meiosis -
much more diverse gene pool. |
|
Advantages |
1. If conditions are
favourable, with asexual reproduction,
lots of offspring are produced quickly because the reproductive life
cycle is fast - e.g. E-coli bacteria can divide every 30 mins and
rapidly colonise a new area.
2. Only one
parent is needed, so the organism can reproduce whenever conditions
are favourable e.g. abundance of food - they don't have to wait for
a mate of the opposite sex!
3. Asexual reproduction requires less
resources e.g. energy - also helps towards an increased rate of
reproduction producing identical offspring.
Dandelions flourish on our lawns with a drop
of rain and sunshine!
|
1. Offspring from sexual
reproduction have a mix of two sets of chromosomes from both
parents. This creates
genetic variation within a given population - giving different
individuals of differing characteristics = phenotypes.
If environmental
conditions change, its more likely that some individuals in the
population will have the right characteristics to survive - and
inherited - survival advantage.
In time this can lead to natural selection and
evolution as the species becomes
better adapted to their new environment and breed more successfully
- the process of natural selection.
We
can do this artificially with selective breeding of plants or
animals for details see
Evolution - theories and evidence, speciation -
new/old species & extinctions, selective breeding notes. |
|
Disadvantages |
1. There is no genetic variation
within the offspring of the population - more likely to be affected
by disease despite a fast rate of reproduction.
Therefore, if environmental
conditions change to become more unfavourable, the whole population
can be affected because there is less chance of genetic variants in
the genome that could
cope with the change e.g. major crop failure.
If a disease infects a population of a
specific plant or animal species that reproduces asexually - much of which can be wiped out due to
lack of a disease resistant plants. It is possible non of the
population plants or animals of a species survive the disease. |
1. Sexual reproduction takes more
time and energy than asexual reproduction and the organisms produce
fewer offspring in their longer life-cycle.
2. Such organisms need to
find and attract a mate of the opposite sex. Two parents are needed for sexual
reproduction - a problem if a potential mate is isolated in the
habitat - 'mates' could be few and far between!
Lots of animal behaviour is about attracting the opposite sex.
See also
Adaptations Part 8 Animal Behaviour |
Organisms
can reproduce by both sexual and asexual reproduction
Examples
Plants
Despite the fact that lots of plants
reproduce sexually - producing seeds sexually, they can also
produce asexually.
Asexual reproduction in plants can take
place in a variety of ways e.g.
(i) strawberry plants produce 'runners' -
stems that grow horizontally away from the plant on the surface
of soil.
At various points on the runner a new
strawberry plant can form which is identical to the original
plant.
(ii) Plants that grow from bulbs like the
familiar daffodil, also reproduce asexually, because new bulbs
can form from the main bulb.
The new bulbs can divide off from the
original bulb to grow into daffodils identical to the parent
plant.
Fungi
The various and numerous species of fungi
are pretty versatile in the reproduction - a specific species
might reproduce by both sexual and asexual reproduction.
These type of species produce and release
spores into the air, these develop into the fungus if they land
on a suitable place.
Spores can be produced sexually or
asexually,.
The spores from asexual reproduction are
genetically identical to the parent fungus and do NOT introduce
genetic variants into the population and are more susceptible to
changes in the environment - narrower gene pool - less chance of
survival.
However, spores from sexual reproduction
produce genetic variants from the random chromosome 'shuffling'
in the process. This increase in variation in the gene pool
increases the chance of individuals surviving if environmental
conditions become less favourable.
Single celled organisms
The parasite that causes malaria is a
microscopic, single-celled organism called a plasmodium.
Malaria is a mosquito-borne infectious disease
that affects humans and other animals.
If a mosquito carrying the parasite bites a
human being the parasite can be transferred to the bloodstream of
bitten person.
The parasite reproduces sexually inside the
mosquito carrier, but reproduces asexually and rapidly in your blood
- giving you an attack of malaria!
Key points -
Summary of ideas
Based on
the syllabus-specifications for students taking the AQA, Edexcel and OCR
GCSE level biology examinations (~US grades 9-10).
Comparing Sexual and Asexual
Reproduction
Introduction
Reproduction is the biological
process by which organisms produce offspring.
There are two main types:
sexual reproduction, which involves the fusion of gametes, and
asexual reproduction, which does not involve gametes and produces
genetically identical offspring.
Each method has distinct advantages and
disadvantages, which are important for understanding genetics, evolution, and
species survival.
Sexual Reproduction
Definition of sexual
reproduction
Sexual reproduction involves the
fusion of male and female gametes (sperm and egg in animals, pollen and ovule in
plants) to form a zygote. This process introduces genetic variation.
Examples of sexual
reproduction
-
Humans & Mammals
– Offspring inherit genetic material from both parents.
-
Flowering Plants
– Pollination leads to fertilization, producing seeds.
-
Fish & Amphibians
– External fertilization occurs in water.
Advantages of sexual
reproduction
-
Genetic Variation
– Offspring inherit a mix of genes, increasing adaptability.
-
Survival Advantage
– Variation allows species to adapt to environmental changes.
-
Disease Resistance
– Some individuals may have immunity to diseases.
-
Selective Breeding
– Humans can breed organisms for desirable traits.
Disadvantages of sexual
reproduction
-
Requires Two Parents
– Finding a mate takes time and energy.
-
Slower Process
– Fertilization and development take longer.
-
Fewer Offspring
– Compared to asexual reproduction, fewer individuals are produced.
-
Risk of Unsuccessful
Fertilization – Gametes may
not meet, preventing reproduction.
Asexual Reproduction
Definition of asexual
reproduction
Asexual reproduction involves a
single parent producing genetically identical offspring (clones) without
gametes.
Examples of asexual
reproduction
-
Bacteria
– Binary fission allows rapid population growth.
-
Plants (Strawberries,
Potatoes) – Runners and tubers
produce clones.
-
Fungi (Yeast, Moulds)
– Spores spread and grow into new individuals.
-
Hydra & Starfish
– Budding and regeneration allow reproduction.
Advantages of asexual
reproduction
-
Rapid Population
Growth – Ideal for colonizing
new environments.
-
No Need for a Mate
– Saves time and energy.
-
Efficient Process
– Faster than sexual reproduction.
-
Stable Traits
– Offspring inherit successful traits unchanged.
Disadvantages of asexual
reproduction
-
No Genetic Variation
– All offspring are identical, limiting adaptability.
-
Vulnerability to
Disease – A single disease can
wipe out an entire population.
-
Limited Evolutionary
Potential – Species may
struggle to adapt to environmental changes.
Comparison Table of
sexual reproduction versus asexual reproduction
| Feature |
Sexual Reproduction |
Asexual Reproduction |
| Number of Parents |
Two |
One |
| Genetic Variation |
High |
None |
| Speed of Reproduction |
Slow |
Fast |
| Adaptability |
High |
Low |
| Energy Requirement |
High |
Low |
| Risk of Disease |
Lower |
Higher |
Summary of learning objectives and key words or phrases
Be able describe and discuss the difference between sexual
reproduction and asexual reproduction.
Be able to describe and discuss the various advantages
disadvantages of sexual reproduction and asexual reproduction.
Be able to describe sexual reproduction or asexual reproduction
in bacteria, flowering plants, fungi spores and malaria plasmodium.
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