Marigold Cell Size and Polyploidy
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Date
2004
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Biological Sciences
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Citation of Original Publication
Hunter, K. L. and R. B. Hunter. 2004. Marigold cell size and polyploidy. Pages 125-133, in Tested studies for laboratory teaching, Volume 25 (M. A. O’Donnell, Editor). Proceedings of the 25th Workshop/Conference of the Association for Biology Laboratory Education (ABLE),
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Abstract
Most animals are diploid, having one set of chromosomes from the male and one from the
female. Polyploid animals, with the exception of some frogs and fish, are usually aborted or die
immediately after birth (Gardner et al., 1991). In contrast, estimates are that about 70% of flowering
plants and 90% of ferns contain three or more sets of chromosomes (Masterson, 1994; Pichersky et
al., 1990). Chromosomes pair at meiosis, therefore most organisms have even sets of chromosomes,
such as tetraploids (4 sets), and hexaploids (6 sets). Those with odd numbers have reduced fertility
(triploids for example) and often reproduce vegetatively.
Many crop plants are polyploid, including coffee, cotton, potatoes, strawberries, sugar cane,
tobacco, wheat and corn. Polyploidy in plants has been investigated since the 1930s to try to
understand and perhaps make use of its effects (Stebbins, 1947). The grain crop triticale, for
example, is a human-generated hybrid polyploid of wheat (Triticum aestivum) and rye (Secale
cereale) formed by scientists containing the complete genomes of both grasses. Plant breeders
induce polyploidy to attempt to increase yield, improve qualities like fruit size or vigor, and to adapt
crops to particular growing conditions (Dewey, 1980; Zeven, 1980). The seedless watermelon and
larger tetraploid grapes are examples. In some instances polyploidy has increased flower, seed or
fruit size, increased photosynthetic or respiration rates, or increased tolerance of extreme
temperatures, drought or flooding (Tal, 1980). However, there are few consistent effects, the
primary one being an increase in cell size (Masterson, 1994; Bennett and Leitch, 1997).
We have developed a lab (Hunter et al., 2002) based on polyploidy and cell size, to introduce
middle school, high school, and college students to several important subjects in biology, including
genetics (chromosomes, meiosis and mitosis, polyploidy), plant anatomy (stomata, air and water
exchange, leaf structure) and cell biology (genome size and cell size). It also allows the use of
simple math in data analysis and utilizes quantitative measurements rather than simple observations.
The lab involves growing marigolds for about one month from seed, and measuring guard cell
(surrounding the stomata) sizes and densities. A modified version of the lab was presented at the
2003 ABLE meeting in Las Vegas.