Sexual and Asexual Reproduction

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• Sexual and Asexual Reproduction

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Importance of Reproduction

• Reproduction is extremely important for the
  survival and evolution of a species.
• Through reproduction, an individual passes on its
  genes to the next generation.

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Types of Reproduction

• Sexual
• Asexual
• Any examples?

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Sexual Reproduction

• Most species reproduce sexually in male and
  female pairs.
• Each parent in a sexually reproducing pair passes
  on half of its genes to its offspring.
• The mix of genes makes each new generation (the
  offspring) different from the previous generation
  (the parents).

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Sexual Reproduction

• This genetic variation provides a very important
  advantage to sexually reproducing organisms the
  ability to adapt more quickly to changing
  conditions in their environment.
• The better-adapted individuals live long enough
  to reproduce sexually and pass on more of their
  genes to the next generation.
• This process is called Natural Selection.

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Sexual Reproduction - Gametes

• In animals, sexual reproduction is the fusion of
  two distinct gametes to form a zygote.
• Gametes are produced by a type of cell division
  called meiosis.
• Gametes can be haploid (containing only one set
  of chromosomes).
• Zygote is diploid (containing two sets of
  chromosomes).

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Types of Fertilization

• External - the eggs (gametes) are fertilized
  outside of the body
• Amphibians and Fish
• Internal - the eggs are fertilized within the
  female reproductive tract
• Mammals and reptiles

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Asexual Reproduction

• Very few species reproduce asexually, a way that
  does not involve male and female.
• In contrast to sexual reproducers, every organism
  that reproduces asexually passes on its entire
  set of genes to the next generation. So, the
  offspring is genetically identical to itself.
  These offspring are produced by mitosis.
• What is the advantage of this?

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Asexual Reproduction

• Since it does not need a sexual partner, a lone
  individual can establish a new population in a
  new territory.
• However, in populations created by asexual
  reproduction, no individual has much of a
  survival or reproductive advantage over any other
  individual.
• This is because they are all so genetically
  similar.

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Asexual Reproduction

• It also means that it will take much longer for
  these populations to evolve in response to change
  going on around them, which makes them especially
  vulnerable to diseases or other natural disasters
  that can wipe them out.
• It is very common in plants, not very common in
  animals.

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Common Forms of Asexual Reproduction

• Budding
• Gemmules
• Fragmentation
• Regeneration
• Parthenogenesis

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Budding

• In this form of asexual reproduction, an
  offspring grows out of the body of the parent.
• Hydras exhibit this type of reproduction.

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Gemmules

• A parent releases a specialized mass of cells
  that can develop into offspring.
• Sponges exhibit this type of reproduction.

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Fragmentation

• The body of the parent breaks into pieces, each
  of which can produce an offspring.
• Planarians exhibit this type of reproduction.

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Regeneration

• If a piece of a parent is detached, it can grow
  and develop into a completely new individual.
• Echinoderms exhibit this type of reproduction.

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Parthenogenesis

• This type of reproduction involves the
  development of an egg that has not been
  fertilized into an individual.
• Animals like most kinds of wasps, bees, and ants
  that have no sex chromosomes reproduce by this
  process.
• Some reptiles and fish are also capable of
  reproducing in this manner.
• Most of these species can switch between Sexual
  and Asexual Reproduction.

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Parthenogenesis
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Advantages Asexual Reproduction

• Animals that remain in one particular place and
  are unable to look for mates would need to
  reproduce asexually.
• Environments that are stable and experience very
  little change are the best places for organisms
  that reproduce asexually.

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Disadvantages Asexual Reproduction

• A disadvantage of this type of reproduction is
  the lack of genetic variation.
• All of the organisms are genetically identical
  and therefore share the same weaknesses.
• If the stable environment changes, the
  consequences could be deadly to all of the
  individuals.

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Summary
Characteristics Sexual Asexual
Number of Parents 2 male and female 1 either male or female
Makeup of Offspring Genetically Different Genetically Identical
Cell division process Meiosis Mitosis
Advantages Variation and Evolution Good to colonize new areas
Disadvantages Slower Disease may affect all