AP BIOLOGY

Detailed explanation-1: -How does an organism become polyploid? Polyploids arise when a rare mitotic or meiotic catastrophe, such as nondisjunction, causes the formation of gametes that have a complete set of duplicate chromosomes. Diploid gametes are frequently formed in this way.

Detailed explanation-2: -Nondisjunction is caused due to inactivation of topoisomerase II, separase or condensin. During anaphase, the cohesin which binds the sister chromatids together is broken by separase. Catenation is removed by condensin and topoisomerase II. Segregation of chromosomes is regulated by spindle assembly checkpoint or SAC.

Detailed explanation-3: -Polyploidy arises as the result of total nondisjunction of chromosomes during mitosis or meiosis. Polyploidy is common among plants and has been, in fact, a major source of speciation in the angiosperms. Particularly important is allopolyploidy, which involves the doubling of chromosomes in a hybrid plant.

Detailed explanation-4: -Polyploidy may occur due to abnormal cell division, either during mitosis, or more commonly from the failure of chromosomes to separate during meiosis or from the fertilization of an egg by more than one sperm.

Detailed explanation-5: -Polyploidy refers to the condition in which there is an increase in the whole set of chromosomes leading to a deviation from its normal ploidy. This situation is caused when the sets of chromatids, even after separating during anaphase, don’t get distributed in the daughter cells due to failure of cytokinesis. Q.