Exam 2 Lesson 13, Chromosomal Aberrations Variations in chromosome number or in chromosome structure are occasionally seen in individuals of a species.
Plants are relatively more tolerant of chromosomal aberrations than are animals.
In addition, by analysis of chromosomes of closely related species it is possible to deduce that alterations in chromosome structure and number occur during speciation. Since there is a close correspondence of genetic material on the arms of these chromosomes, it is clear that they are homologous. Likewise, comparison of the 23 pairs of human chromosomes with the 24 pairs of chimpanzee reveals that two acrocentric chromosomes in chimpanzees have apparently fused to form the single metacentric chromosome that is found in humans. Polyploidy Variations in chromosome number that involve duplication of all the chromosomes in the entire genome is called polyploidy . Polyploidy occurs commonly in plants, in fact most crop species, including cotton, and wheat are polyploid.