POLYPLOIDY
This assignment involves the exploration of the topic of polyploidy. Your task is to
utiluize the resources below and produce a Prezi/powerpoint or poster from Glogster.
The questions you are to address are the following:
What is polyploidy?
What are some sample chromosome arrangements in polyploidy?
What are some examples of polyploid organisms?
What are some mechanisms of polyploidy? (at least 2)
How is polyploidy involved in the production of “seedless” varieties of fruits and
vegetables?
How can polyploidy contribute to speciation (2 examples)?
What is one advantage and one disadvantage of polyploidy?
5 fabulous facts about polyploidy.
Suggested Resources: Feel free to find others but these are good basic sescriptions:
http://www.nature.com/scitable/topicpage/polyploidy-1552814
http://www.polyploidy.org/index.php/Information:How_are_polyploids_formed
http://www.youtube.com/watch?v=Z6W2dhLRhw0
http://waynesword.palomar.edu/hybrids1.htm
The following information is from
(http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Polyploidy.html)
Polyploidy in plants
Polyploidy is very common in plants, especially in angiosperms. From 30% to 70% of
today's angiosperms are thought to be polyploid. Species of coffee plant with 22, 44, 66,
and 88 chromosomes are known. This suggests that the ancestral condition was a plant
with a haploid (n) number of 11 and a diploid (2n) number of 22, from which evolved the
different polyploid descendants.
In fact, the chromosome content of most plant groups suggests that the basic angiosperm
genome consists of the genes on 7–11 chromosomes. Domestic wheat, with its 42
chromosomes, is probably hexaploid (6n), where n (the ancestral haploid number) was 7.
Some other examples:
Probable
ancestral Chromosome
Plant
haploid
number
number
domestic oat
7
42
Ploidy
level
6n
peanut
10
40
4n
sugar cane
10
80
8n
banana
11
22, 33
2n, 3n
white potato
12
48
4n
tobacco
12
48
4n
cotton
13
52
4n
apple
17
34, 51
2n, 3n
Polyploid plants not only have larger cells but the plants themselves are often larger. This
has led to the deliberate creation of polyploid varieties of such plants as watermelons,
marigolds, and snapdragons.
POLYPLOIDY
Polyploidy and Speciation
When a newly-arisen tetraploid (4n) plant tries to breed with its ancestral species (a
backcross), triploid offspring are formed. These are sterile because they cannot form
gametes with a balanced assortment of chromosomes.
However, the tetraploid plants can breed with each other. So in one generation, a new
species has been formed.
Polyploidy even allows the formation of new species derived from different ancestors.
In 1928, the Russian plant geneticist Karpechenko produced a new species by crossing a
cabbage with a radish. Although belonging to different genera (Brassica and Raphanus
respectively), both parents have a diploid number of 18. Fusion of their respective
gametes (n=9) produced mostly infertile hybrids.
However, a few fertile plants were formed, probably by the spontaneous doubling of the
chromosome number in somatic cells that went on to form gametes (by meiosis). Thus
these contained 18 chromosomes — a complete set of both cabbage (n=9) and radish
(n=9) chromosomes.
Fusion of these gametes produced vigorous, fully-fertile, polyploid plants with 36
chromosomes. (They had the roots of the cabbage and the leaves of the radish.)
These plants could breed with each other but not with either the cabbage or radish
ancestors, so Karpechenko had produced a new species.
The process also occurs in nature. Three species in the mustard family (Brassicaceae)
appear to have arisen by hybridization and polyploidy from three other ancestral species:

B. oleracea (cabbage, broccoli, etc.) hybridized with B. nigra (black mustard)

→ B. carinata (Abyssinian mustard).
B. oleracea x B. campestris (turnips) → B. napus (rutabaga)
B. nigra x B. campestris → B. juncea (leaf mustard)

Modern wheat and perhaps some of the other plants listed in the table above have
probably evolved in a similar way.
Polyploidy in animals
Polyploidy is much rarer in animals. It is found in some insects, fishes, amphibians, and
reptiles. Until recently, no polyploid mammal was known. However, the 23 September
1999 issue of Nature reported that a polyploid (tetraploid; 4n = 102) rat has been found
in Argentina.
Polyploid cells are larger than diploid ones; not surprising in view of the increased
amount of DNA in their nucleus. The liver cells of the Argentinian rat are larger than
those of its diploid relatives, and its sperm are huge in comparison. Normal mammalian
sperm heads contain some 3.3 picograms (10-12 g) of DNA; the sperm of the rat contains
9.2 pg.
Although only one mammal is known to have all its cells polyploid, many mammals have
polyploid cells in certain of their organs, e.g, the liver. [More]