BIOL 202 Lecture Notes - Lecture 16: Nondisjunction, Brassicoraphanus, Homologous Chromosome
20 Feb 2018
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Document Summary
Allopolyploids: have chromosomes from two closely-related species, making it a hybrid. Division only occurs properly if two homologous chromosomes are present in the: better tolerated in plants. Cross between a radish and a cabbage: both parents have gametes with n=9 chromosomes: gave off a sterile f1 hybrid. 2n = 18, however the chromosomes from cabbage and from parent don"t count as homologous: disrupting meiosis to create tetraploids leads to homologous pairing: meiosis now proceeds as normal and the tetraploid is not sterile. New species: crossing back to either parents leads to infertility of offspring. Crossing raphanobrassica back to the parent strain leads to infertility. If you cross it back to the cabbage, the cabbage genes form homologous pairs while the radish genes do not, and vice-versa. Allopolyploidy leads to the formation of new species in nature, particularly in plants: ex: the genus brassica, wheat. Viable organisms with one set of chromosomes.
