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43.1 Reproduction Methods
By the end of this section, you will be able to discuss advantages and disadvantages of asexual and sexual reproduction.
There are advantages and disadvantages to both methods.
Large numbers of offspring can be produced quickly and a single individual can produce offspring asexually.
Asexual reproduction is an effective means of reproduction in a stable environment because all the offspring will be adapted to that environment.
All the offspring are genetically identical and may not have the genetic variation to survive in new or different environments.
The rapid rates of asexual reproduction may allow for a quick response to environmental changes.
When an individual does not need a mate to reproduce, colonization of new habitats may be easier.
The genetic diversity of sexually produced offspring is thought to give species a better chance of surviving in an unpredictable or changing environment.
The ability to colonize new habitats can be limited by the fact that both sexes must be present, as species that reproduce sexually must maintain two different types of individuals.
Asexual reproduction can occur in some single-celled and multi-celled organisms.
There are many ways in which animals reproduce.
An organisms splits into two separate organisms after a period of growth.
Some unicellular organisms go through a process called mitosis.
A second individual is formed in other organisms.
In many asteroid echinoderms, this process occurs when the central disk is split.
The sea anemones and coral polyps reproduce through fission.
Coral polyps reproduce asexually.
Some animals that experience Budding are corals and hydras.
There is a video of a hydra budding.
A separate individual will regrowth if the animal is capable of being splintered.
In many sea stars, asexual reproduction is accomplished by fragmenting.
Sea stars can be killed by cutting them in half and throwing them back into the ocean.
The workers will be preyed upon by twice as many sea stars as the oysters and clams because the two parts can each regenerate a new half.
Turbellarians, annelid worms, and poriferans all suffer from degradation.
Sea stars can reproduce.
A fragment from a sea star is developing into a new person.
There is a noticeable difference in the size of the individuals in both fragmentation and fission.
Depending on the process and the species, the resulting offspring can be either haploid or diploid.
Water fleas, rotifers, aphids, stick insects, some ants, and bees are parthenogenesis.
haploid males are produced by bees using parthenogenesis.
If eggs are fertilized and fed a special diet, diploid females will develop and a queen will be produced.
Some animals reproduce through parthenogenesis.
Parthenogenesis has been observed in animal species that were separated by sex in zoos.
Two female Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic young when the females have been isolated from males.
Sexual reproduction is the combination of haploid reproductive cells from two individuals to form a third child.
The offspring of sexual reproduction have novel combinations of genes.
In unpredictable environments, this can be an advantage.
As humans, we are used to thinking of animals as having two genders--male and female.
There are many variations on this theme in the animal kingdom.
They can self-fertilize or mate with another species and produce offspring.
Barnacles and clams are examples of animals that have self fertilization.
Many animals are hermaphrodites.
Up to one hundred eggs can be produced when two individuals mate.
Sex determination is determined by the presence of X and Y chromosomes.
There are two types of individuals who are male and female.
The Y chromosomes cause the development of male and female characteristics.
Some insects and plants have the XY system.
The presence of Z and W chromosomes can affect the sex determination of a bird.
In mammals, the W is important in determining the sex of the individual.
This system is used by fish, crustaceans, insects, and reptiles.
The sex of some species is determined by the environment.
Sex determination in some crocodiles and turtles is dependent on the temperature during critical periods of egg development.
This is referred to as temperature dependent sex determination.
Males and females can be produced in turtles by cooler temperatures and warm temperatures.
Moderate temperatures produce males and both warm and cool temperatures produce females in crocodiles.
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