Cyto-num - CYTOGENETICS; CHROMOSOMAL ABERRATIONS PART I:...

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CYTOGENETICS; CHROMOSOMAL ABERRATIONS PART I: Changes in Chromosome Number Changes in the number of sets of chromosomes per cell - EUPLOIDY- Each genome has one complete set of chromosomes Humans have 23 chromosomes per set (genome) N = 23 Corn plants have 10 chromosomes per set N= 10 Flies have 4 chromosomes per set N= 4 'Ploidy ' levels are defined by the number of sets of chromosomes per cell Most higher organisms have 2 sets of chr0mosomes in each somatic cell and thus are said to be "diploid ". They are said to be 2N. Gametes (eggs or sperm) have one set of chromosomes so are haploid (or monoploid) (1N) Some cells in liver and bronchial tissues have 4 sets (4N) so are tetraploid cells. However it is very rare to find " polyploid " animals capable of survival and reproduction. (The term polyploid is often used any time more than 2 sets of chromosomes are found.) Dr. Bickham in our WFS department discovered a "triploid" species of turtles in South America that reproduces by parthenogenesis (unreduced, unfertilized eggs develop into adults. Human triploids occur rarely. While not grossly malformed, the vast majority are aborted as fetuses or are stillborn. Most are thought to result from simultaneous fertilization of an egg by two sperm. (How many chromosomes would be present in the cells of these individuals?) By contrast, polyploidy is very common in plants. Many ornamental flowers are tetraploids or hexaploids; they produce gametes with 2 and 3 sets of chromosomes respectively. As long as every chromosome has a partner for meiosis, functional gametes can form. Gametes without exact whole sets of genomes are almost always non-functional and non-viable. The cotton we grow in Texas (
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This note was uploaded on 04/29/2008 for the course GENE 310 taught by Professor Magill during the Spring '08 term at Texas A&M.

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Cyto-num - CYTOGENETICS; CHROMOSOMAL ABERRATIONS PART I:...

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