Recombination: Creating variation in gametes

  • 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.

Crossing-over at prophase I (pachytene) and independent assortment at metaphase I are responsible for rearranging DNA during meiosis producing gametes that are genetically different.

 

Crossing-over

Crossing-over is responsible for recombining genes on the same homologous chromosome pair (cytologically linked loci) and involves the exchange of non sister chromatid DNA through breakage of two non sister chromatids at the same place. The broken ends of the chromatids then cross reunite with non sister chromatids. The chromatids of the homologous chromosomes now contain heterogenous regions if the loci were heterozygous to start with. At anaphase I the bivalent breaks up into the two chromosomes which move to opposite poles. At anaphase II the chromatids of the chromosomes separate into separate gametes. The gametes that result from one meiotic event may be genetically different depending whether the loci that recombined were heterozygous or not.

Crossing-over between two heterozygous loci:

• From one meiocyte four different gametes are produced.
• The outcome of this is event is two parental gametes (50%), AC and ac; and two recombinant gametes (50%), Ac and aC.
• You will notice that the A/a locus segregates at anaphase I, first division segregation. That means that the A-alleles separates from the a-allele at anaphase I. The C/c locus becomes heterogenous with crossing-over and segregates at anaphase II, second division segregation. The C-allele separates from the c-allele at anaphase II.

Independent assortment

Independent assortment involves the independent arrangement of bivalents on the equator at metaphase I and rearranges loci on non homologous chromosomes (non cytologically linked loci). Gametes produced from different cells undergoing meiosis are genetically different if loci were heterozygous to start with.

Independent assortment between two heterozygous loci:

• If the parental gametes are AB and ab, you will notice that one meiocyte produces either parental gametes or recombinant gametes, not both types.
• The outcome of this is event is two parental gametes (50%) and two recombinant gametes (50%).