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Polyploidy worksheetDeveloped by Andreas Madlung1, Ed Himelblau2 and Jim Birchler3
Ploidy refers to the number of complete chromosome sets in an organism. Humans, for example, have 2x 23 chromosomes (i.e. 23 pairs of homologous chromosomes) in most cells.That state is referred to as “diploid” and thus 23 chromosomes constitute one “basic set”. Cells with only one set are called “haploid”. Any cell containing three or more multiples of the basic set (3x, 4x, 5x, etc.) are called “polyploid”. While polyploidy is common in plants, it is less common in animals and very rare in mammals. In fact, small deviations from the regular chromosome number in humans can cause detrimental effects, such as Down Syndrome, which occurs when humans have three, rather than two copies of one single chromosome, chromosome number 21.
A B C D
a b
c d
What happens to maize when the ploidy is changed? In the picture on the left you see four maize plants from left to right with increasing ploidy (haploid, diploid, triploid, tetraploid).
A. Using the meter stick leaning next to plant A as a reference (in the picture exactly 1m long) and a regular ruler, determine the height of each plant.
A ________ cm B ________ cm C ________ cm D ________ cm
B. On the left you see four pictures of the entire chromosome set of one cell of each plant. Count the chromosome numbers in each and match the capital letters A - D from the plants above with the corresponding chromosome set .
A ____ B ____ C ____ D ____
C. According to your data, what is the basic chromosome number of maize?
D. Judging from your analysis, how would you describe the effect of increasing ploidy on overall biomass in maize?
Picture credits: Anjali Dogra, Zhi Gao, and Hong Yao. Chromosomes appear different in size due to varying magnification only.
Picture credit: Nicole Riddle
Fruit yield in polyploids
Many of today’s agricultural crops are polyploid. Sometimes, an increase in ploidy results also in an increase in organ size. Not in all cases this means a greater total yield in biomass, though.
Nomenclature in polyploids
The chromosome number in somatic (body) cells of a species is commonly given as 2N while the number of chromosomes in a gamete (sex cell) regardless of ploidy is N. X is the “most likely base number” of chromosomes. Recall that in humans this number is 23. Therefore, in humans one would say 2N = 2X = 46.A tetraploid cell is described as 2N = 4X. A human tetraploid cell would therefore be
2N = 4X= 92.
Using the information from the previous page, answer the following questions:
A. What is the base number X of chromosomes in maize?
B. What is N for each of these ploidy levels in maize?diploid: N=______; tetraploid: N=______
C. Determine the gametic and somatic chromosome number for the diploid and octoploid strawberry species shown above. (The diploid strawberry has 14 chromosomes in somatic cells.)
Fragaria vesca: ___N = ____X =Fragaria virginiana: ___N=____X =
Fragaria vesca (Wild Strawberry)(diploid)picture credit: www.luontonetti.com
Fragaria virginiana and Fragaria chilioensis(octoploid)picture credit: www.firestonepacificfoods.com
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
diploid tetraploidpicture credit: Akio Kato.
Determination of ploidy level
To determine the level of ploidy in an unknown species the best way is to make a chromosome spread like you saw on page 1 and count the chromosomes. But there is an easier way to determine the relative ploidy of two individuals of the same species. To tell if one or the other has a higher ploidy level, a surprisingly good diagnostic tool is to measure the size of the stomata on the leaf. Below are three leaf imprints of maize, each taken at the same magnification. Using a ruler, measure the length of 5 stomata on each picture, calculate the average and order the pictures in ascending ploidy.
Picture A shows the leaf of a _____________maize leaf.Picture B shows the leaf of a _____________maize leaf. Picture C shows the leaf of a _____________maize leaf.
A
C
B
terms to use:diploid, tetraploidhexaploid
photo credit: Hong Yao
Contact information: 1: Department of Biology, University of Puget Sound, Tacoma, WA, 98416, email:[email protected] 2: California Polytechnical University, San Luis Obispo, CA 93407, email:[email protected]; 3:University of Missouri, Columbia, MO 65211, email: [email protected]
