bio214g - Biology 214/414 2009 Packet#6 Suggested problems...

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Biology 214/414 2009 P a c k e t # 6 Suggested problems: Chapter 8: 1, 2, 3, 4, 5, 6, 8, 13, 14, 26, 30 Variations in chromosome number and structure I. These topics are most often studied using “cytological ” techniques (ie, those using microscopes); for chromosome study this is known as “cytogenetics ”. a. Typically mitotic cells with metaphase chromosomes are studied. i. The chromosomes are stained with various dyes (both fluorescent and non-fluorescent (eg, quinacrine, Giemsa, acridine orange). ( Figures 7-6, 7; page 198; Figures 8-4, 6, 7 ) ii. These result in reproducible banding patterns of various types which allow identification of individual chromosomes and determination of their integrity. iii. The complete chromosome complement of a cell is its “karyotype ”. 1. The normal human karyotype, for example, has 46 chromosomes, 22 pairs of autosomes numbered (more or less) from largest (#1) to smallest (#22) + 2X or X and Y. ( Figure 7-6 ) 2. Since the chromosomes are viewed at metaphase, each has two chromatids joined at the centromere, which can be located at various locations depending on the chromosome. Typically this is nearer one end than the other, resulting in short arms (denoted “p”) and long arms (denoted “q”); for example, the long arm of chromosome 10 is denoted as “10q”. iv. some useful terms: 1. “euploid ” (adj.) and “euploidy ” (noun)—refer to the situation in which there are complete chromosome sets. 2. “polyploid ” (adj.) and “polyploidy ” (noun)—refer to the situation in which there are extra complete
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sets of chromosomes (eg, 3n, 4n, 5n….situations); polyploids are a subset of euploids. 3. “aneuploid ” (adj.) and “aneuploidy ” (noun)—refer to the situation in which a particular chromosome or chromosomal segment is under or over represented. II. Polyploids are fairly common in plants but rare in animals. a. Polyploid plants tend to produce larger seeds and fruits and greater yields than diploid plants (examples are: wheat, coffee, potatoes, bananas, some apples, strawberries, cotton, roses, tulips, chrysanthemums). ( Figures 8-8, 11 ) b. But many are sterile—the extra chromosome sets result in segregation during meiosis I occurring in irregular ways. i. For example in triploids, instead of pairs of homologues there are either three homologues paired in first meiosis or a pair plus a single homologue. In either case there is uncertainty in segregation so that for each chromosome a product from the first meiotic division might get 0-3 copies; when considered over all chromosomes, these cells (and gametes from them) will have gross chromosome imbalances and will be inviable. ( Figure 8- 3 ) This gives seedless varieties, such as of watermelons and bananas. ii.
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bio214g - Biology 214/414 2009 Packet#6 Suggested problems...

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