Learn what is meant by polyploidy and discover the different types of polyploidy. See the significance of ploidy and the relevance of polyploidy in plants.
Updated: 01/26/2022
What is Polyploidy? | Polyploidy Number & Types
What is Polyploidy?
Polyploidy is a heritable condition where an organism contains more than two complete sets of chromosomes. Polyploidy arises as a result of nondisjunction in human cells. Nondisjunction happens when members of a pair of homologous chromosomes fail to separate during meiosis. In humans, this condition is lethal. Certain organisms including angiosperm plants, some salamanders, frogs and leeches are polyploid. Due to the high frequency of polyploids in these species, these organisms are well adapted for their environment and have unique advantages.
What Does Ploidy Mean?
The term polyploidy is a general term for a chromosomal alteration in which an organism has two or more complete sets. The prefix poly means many and the term ploidy indicates sets of chromosomes. Therefore, a direct translation is many sets of chromosomes. Ploidy level refers to the number of sets of chromosomes in a somatic cell. Somatic cells include all of the cells in your body, excluding the sex cells. Ploidy number (n) refers to the haploid number of chromosomes for that particular organism. Haploid refers to the number of chromosomes in a single set of unpaired chromosomes, and the haploid number is the number of chromosomes found in that particular organism's sex cells. Organisms, like bacteria, can be classified as monoploid (n). Humans are classified as diploid (2n). Polyploidy organisms can be classified as triploid (3n), tetraploid (4n), hexaploid (6n) and octoploid (8n). The number preceding the n indicates how many sets of chromosomes the offspring has. Individuals that inherit an odd number of sets are typically infertile because the chromosomes cannot pair up correctly during meiosis.
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Polyploidy is fairly common in the plant kingdom. Roughly 50% of all angiosperms are polyploidy. This mechanism is considered a driving force in evolution. Organisms can be aneuploidy, a condition in which the offspring has an abnormal number of a particular chromosome. The most common type of aneuploidy is trisomy 21 (Down Syndrome). Down Syndrome is a condition in which the offspring has 3 of chromosome 21 resulting in the offspring having 47 chromosomes. Human cells should contain 46 chromosomes and are classified as diploid organisms because they contain 2 sets of chromosomes.
Types of Polyploidy
Organisms that have more than two complete sets of chromosomes are classified as polyploidy. Polyploids can be classified as autopolyploids or allopolyploids.
Autopolyploids
All organisms classified as autopolyploid have identical genomes. These organisms are derived from a single parent species usually through self fertilization. Autopolyploids contain more than two complete copies of the genome. In agriculture, both watermelons and bananas are triploid (3n) and produce sterile seeds.
Allopolyploids
Allopolyploids are more common than autopolyploids due to the ability to potentially produce fertile offspring. These species are derived from 2 or more sets of chromosomes and the additional set comes from another species. Wheat is an example of an allopolyploid and contains 6 sets of chromosomes (6n).
Polyploidy in Plants and Animals
Polyploidy is much more common in plants than animals. Angiosperm plants are commonly polyploid, which has been a driving force of speciation in this species. Plants are more commonly polyploidy because they lack separate sexes and have the ability to self-pollinate. Wheat and bananas are two common foods humans consume that are polyploid. Crops that humans consume are often induced to be polyploid through genetic modification, making them larger than they are naturally. It is much rarer in animals because it is consequential to have extra allele copies for every gene. Most commonly in animals are invertebrates such as leeches, flatworms, and brine shrimp. Each of these organisms contain extra sets of chromosomes. Polyploidy in animals is seen more commonly in fish and amphibians.
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In humans, polyploidy is a lethal event. Polyploidy results from nondisjunction, in which homologous chromosomes fail to separate properly during meiosis. This genetic mutation results in the human offspring containing extra sets of chromosomes. The vast majority of polyploidy (typically triploidy due to the sperm) pregnancies end in miscarriage. While this condition is lethal in humans offspring, some human cells are actually polyploidy. For instance, the specialized tissues of both the liver and placenta are polyploid. These cells acquire more than two sets and can increase the size of the organism.
Lesson Summary
Polyploidy is a genetic condition in which an organism contains more than two complete sets of chromosomes. The prefix poly means many and ploidy means sets of chromosomes. This heritable condition arises as a result of nondisjunction in human cells. Nondisjunction happens when members of a pair of homologous chromosomes fail to separate during meiosis. In biology, the number of chromosomes in an organism is indicated through a ploidy level and ploidy number. Ploidy level refers the the number of sets of chromosomes found in a particular organism and ploidy number refers to the haploid number of chromosomes for that particular species. The haploid number is the number of chromosomes found in the sex cell for that particular organism and is a single set. The number preceding the n indicates how many sets of chromosomes the offspring has. Polyploids can be classified as autopolyploids or allopolyploids. Autopolyploids are organisms that are derived from a single parent species usually through self-fertilization and contain identical genomes. Examples include watermelon and bananas. Allopolyploids are derived from 2 parents and the additional set comes from another species. These offspring are able to reproduce and are much more common. An example of allopolyploids is wheat. Additionally, organisms can be aneuploidy, a condition in which the offspring has an abnormal number of a particular chromosome. The most common type of aneuploidy is Down Syndrome (trisomy 21). Individuals born with Down Syndrome have 3 of chromosome 21 resulting in 47 total chromosomes. Human cells should contain 46 chromosomes and are classified as diploid organisms because they contain 2 sets of chromosomes.
While common in plants, this condition is lethal in humans. Certain organisms like angiosperm plants, some salamanders, frogs and leeches are polyploid. Plants are more commonly polyploidy because they lack separate sexes and have the ability to self-pollinate. In humans, polyploidy is a lethal event. However, certain specialized tissues in the liver and placenta are polyploid. The vast majority of polyploidy pregnancies end in miscarriage.
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Frequently Asked Questions
What is polyploidy?
The term polyploidy is a general term for a chromosomal alteration in which an organism has two or more complete sets. Polyploidy results from nondisjunction, when chromosomes fail to separate during meiosis.
What is aneuploidy and polyploidy?
Aneuploidy is a condition in which an organism has an abnormal number of a particular chromosome. An example of aneuploidy is trisomy 21 (Down's syndrome) in which the individual has 3 of chromosome 21 giving the individual 47 instead of 46 chromosomes. Polyploidy occurs when an organism contains more than two complete sets of chromosomes.
What is polyploidy and how does it affect plants?
Polyploidy, a condition in which organisms are born with extra sets of chromosomes, is fairly common in the plant kingdom. Roughly 50% of all angiosperms are polyploidy. This condition is considered to be a driving force in evolution giving these plants an advantage.
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Polyploidy Number & Types | What is Polyploidy?
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