Polyploidy: Multiple sets of chromosomes

  • strict warning: Non-static method view::load() should not be called statically in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/views.module on line 823.
  • strict warning: Declaration of views_plugin_display::options_validate() should be compatible with views_plugin::options_validate(&$form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/plugins/views_plugin_display.inc on line 0.
  • strict warning: Declaration of views_plugin_display_block::options_submit() should be compatible with views_plugin_display::options_submit(&$form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/plugins/views_plugin_display_block.inc on line 0.
  • strict warning: Declaration of views_plugin_display_page::options_submit() should be compatible with views_plugin_display::options_submit(&$form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/plugins/views_plugin_display_page.inc on line 0.
  • strict warning: Declaration of views_handler_field_broken::ui_name() should be compatible with views_handler::ui_name($short = false) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/handlers/views_handler_field.inc on line 0.
  • strict warning: Declaration of views_handler_sort_broken::ui_name() should be compatible with views_handler::ui_name($short = false) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/handlers/views_handler_sort.inc on line 0.
  • strict warning: Declaration of views_handler_filter::options_validate() should be compatible with views_handler::options_validate($form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/handlers/views_handler_filter.inc on line 0.
  • strict warning: Declaration of views_handler_filter::options_submit() should be compatible with views_handler::options_submit($form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/handlers/views_handler_filter.inc on line 0.
  • strict warning: Declaration of views_handler_filter_broken::ui_name() should be compatible with views_handler::ui_name($short = false) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/handlers/views_handler_filter.inc on line 0.
  • strict warning: Declaration of views_handler_filter_many_to_one::init() should be compatible with views_handler_filter::init(&$view, $options) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/handlers/views_handler_filter_many_to_one.inc on line 0.
  • strict warning: Declaration of views_handler_filter_term_node_tid::value_validate() should be compatible with views_handler_filter::value_validate($form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/modules/taxonomy/views_handler_filter_term_node_tid.inc on line 0.
  • strict warning: Declaration of views_plugin_row::options_validate() should be compatible with views_plugin::options_validate(&$form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/plugins/views_plugin_row.inc on line 0.
  • strict warning: Declaration of views_plugin_row::options_submit() should be compatible with views_plugin::options_submit(&$form, &$form_state) in /home/dvdfos0/public_html/geneticssuite/sites/all/modules/views/plugins/views_plugin_row.inc on line 0.

A polyploid has more than 2 sets of chromosomes and is prevalent in plants but rare in animals. Many grass species are polyploid; some species can have more than 10 sets of chromosomes.
 

Polyploidy occurs in some animals, such as goldfish, salmon, and salamanders, but is especially common among ferns and flowering plants, including both wild and cultivated species. Many grass species are polyploid. Wheat, for example, has strains that are diploid, tetraploid with the common name of durum or macaroni wheat, and hexaploid with the common name of bread wheat. 

The number of basic chromosomes sets (x) in a somatic cell determines the ploidy of the organism. If the different chromosomes set are complete - contain all the chromosomes - such an organism is referred to as a euploid.

Naming  of polyploids

            Organism with 1 set of chromosomes (x) = monoploid
            Organism with 2 sets of chromosomes (2x) = diploid  

Polyploids
 
            Organism with 3 sets of chromosomes (3x) = triploid 
            Organism with 4 sets of chromosomes (4x) = tetraploid 
            Organism with 5 sets of chromosomes (5x) = pentaploid
            Organism with 6 sets of chromosomes (6x) = hexaploid
            Organism with 7 sets of chromosomes (7x) = heptaploid
            Etc.

Diplioidy and  polyploidy

Classes of polyploids

Autopolyploids

Autopolyploids are polyploids of which all the sets of chromosomes have the same karyotype. See figure above.

If a set of chromosomes (also referred to as a genome) is represented by “A” then the genome compositions of a diploid and autopolyploids are:
 Diploid = AA
 Triploid = AAA (uneven polyploid)
 Tetraploid = AAAA (even polyploid)
 Pentaploid = AAAAA (uneven polyploid)

In autopolyploids, a particular chromosome has the same number of homologous members as the ploidy:
 In triploids each chromosome occurs in groups of 3 homologues.
In tetraploids each chromosome occurs in groups of 4 homologues.
In pentaploids each chromosome occurs in groups of 5 homologues.
 Etc.

Allopolyploids

Allopolyploids are polyploids of which the sets of chromosomes have different karyotypes. The chromosomes of the different genomes are also unable to synapse during meiosis, because of the extent of karyotypic differences between the genomes. Different letters of the alphabet is used to indicate alloploid genomes.

Examples of allopolyploids:
 Triploid = AAB 
 Tetraploid = AABB 
 Pentaploid = AABBC 

Segmental allopolyploids

Segmental allopolyploids are polyploids of which the sets of chromosomes have different karyotypes. The chromosomes of the different genomes are able synapse during meiosis to varying degrees – depending on the extent of the karyotypic differences between the different genomes. The same letter of the alphabet is used to indicate segmental genomes, using sub- or superscripts to indicate that they are different. 

Examples of allopolyploids:
 Triploid = A1A1A2
 Tetraploid = A1A1A2A2 
 Pentaploid = A1A1A2A2A
 

Characteristics of polyploids

• Polyploids tend to be larger than their diploid counterparts. They have larger cells with increased volume.
• Polyploids tend to display semi-sterility or sterility.
• Polyploid plants tend to display heightened susceptibility to frost damage and higher resistance to pests and pathogens. 
• Polyploid plants tend grow slower and flower later.
 

Plant breeders created artificial harnessing these characteristics.

Chromosome numbers of some well-known species

Species

Zygotic chromosome number 2n

Basic chromosome number x

Ploidy

Homo sapiens 46 23 Diploid (2x)
Zea maize 20 10 Diploid (2x)
Nicotiana tabacum 44 11 Tetraploid (4x)
Rosa canina 35 7 Pentaploid (5x)
Triticum aestivum 42 7 Hexaploid (6x)