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Allopolyploid: Definition, Speciation & Example

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  • 0:04 Background on Ploidy
  • 1:06 Allopolyploidy & Speciation
  • 2:13 An Animal Example
  • 3:03 Some Plant Examples
  • 4:15 Lesson Summary
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Lesson Transcript
Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

This lesson will describe what allopolyploidy means and how it occurs. Speciation through allopolyploidy and examples of allopolyploidy will be covered as well.

Background on Ploidy

Eye color, ear shape, and nose size are just a few of the characteristics that are determined by the genes on the chromosomes in your cells. Your chromosomes came from the two parents that created you. Humans, dogs, cats, and almost every other mammal have two sets of chromosomes that create every detail of the body.

The number of sets of chromosomes in an organism is known as the ploidy number. Having two sets of chromosomes means that you are diploid or 2n. There are other animals and several species of plants that are polyploidy meaning that they have more than two sets of chromosomes. They may be triploid or 3n, tetraploid or 4n, hexaploid or 6n, etc.

One or more sets of chromosomes come from parents of the same species that reproduced to create the organism. The chromosomes are passed down through many generations and contain genes that are part of the same species. Having sets of chromosomes that originated within the same species only is autoploidy. This is the rule for how chromosomes are passed on to offspring.

Allopolyploidy & Speciation

Ploidy has exceptions to the rule just like anything else in life. There are times when organisms may contain two or more sets of chromosomes that are from different species. When this occurs, we refer to this as allopolyploidy. It may help to remember this if you think about the prefix, 'allo-,' meaning 'other' or 'different,' and that 'poly-' means 'many.'

I bet you are wondering how the genetic information from different species ends up in an organism? Well, the gametes from two different species will come together and form a viable offspring. The offspring will have the genetic make-up for two different species, which makes it a hybrid and therefore a different species. The creation of a new species is known as speciation. Almost all allopolyploids are infertile due to not having full sets of chromosomes. Full sets of chromosomes are needed for the pairing of chromosomes during the process of meiosis.

There is one huge requirement that has to be met in order for allopolyploidy to occur on its own. The organisms must be sexually compatible. This essentially means that it must be possible to get the male and female gametes together through whatever reproductive mechanism is used by both species.

An Animal Example

Although allopolyploidy rarely happens in animals, there is an animal that you've probably heard of, mules. Mules are the result of a diploid male donkey and a diploid female horse reproducing. The donkey has 62 chromosomes, while the horse has 64 chromosomes. Therefore, the donkey gamete has 31 chromosomes, and the horse game has 32 chromosomes, making the resulting infertile mule to have 63 chromosomes.

They're not considered to have a set ploidy number since they have one unpaired chromosome. This unpaired chromosome causes problems with fertility, especially for the male mules. Male mules are all sterile. Female mules may sometimes be able to reproduce with purebred donkeys or horses.

Physical form and the physiology of sex makes this pretty much impossible for almost all animals.

Some Plant Examples

Allopolyploidy tends to occur more so in plants. In actuality, it's very common in plants and you encounter allopolyploid plants all the time. Some of your clothes and bed sheets may contain our next example of allopolyploidy, if they contain cotton. Gossypium species of cotton are formed from the combination of two diploid cotton plants, making them allotetraploids. Here '-tetra' implies four, or four sets of chromosomes. It's believed that the hybrid cotton plant species were produced naturally and prior to continental drift since the two parent species are found on different continents.

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