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Ferns

Ferns brought about the first true leaves; today they inhabit moist, shady habitats.

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A Plant With More Chromosomes Than You

A Plant With More Chromosomes Than You

Credit: Steve Parker
Source: http://commons.wikimedia.org/wiki/File:Tree_Fern_at_Kew_Garden_(Steve_Parker).jpg#mediaviewer/File:Tree_Fern_at_Kew_Garden_(Steve_Parker).jpg
License: CC BY-NC 3.0

You might be surprised to learn that some species of ferns have over 1200 chromosomes. That?s over 26 times more chromosomes than humans? measly 46! In fact, the world record holder for the most chromosomes is the fern Ophioglossum reticulatum with 1260 chromosomes!

Amazing But True!

  • Humans and most other animals are diploid, meaning that they have two sets of chromosomes.
  • Through the course of evolution, some species have generated multiple copies of their chromosomes due to errors in meiosis, when the sex cells or gametes are produced. Gametes normally have half the number of chromosomes as other cells in the body, but errors can occur when the chromosomes don?t separate properly, creating multiple copies. Having more than two copies of each chromosome is called polyploidy.

Credit: Ilmari Karonen
Source: http://commons.wikimedia.org/wiki/File:Polyploidization.svg
License: CC BY-NC 3.0

Polyploidy can occur when a diploid cell (2n) does not halve its chromosomes during meiosis, and instead produces two 2n gametes with the same number of chromosomes as the original cell. When 2n gametes combine, they create a zygote with double the original number of chromosomes (4x, tetraploid). [Figure2]

  • Polyploidy is common in plants, with the fern taking it to the extreme with its thousands of chromosomes. It also occurs in some species of insects, fish, amphibians, crustaceans, and reptiles.
  • Watch this video to learn more about why ferns and some other organisms have so many chromosomes:

https://www.youtube.com/watch?v=5LXEQIyOYto

Show What You Know

Read the links below to learn more about polyploidy in ferns and other organisms. Then answer the following questions.

  1. What organism has the smallest number of chromosomes?
  2. Why does Dr. Paul Wolf think that ferns might have so many chromosomes compared to other organisms?
  3. What usually happens in mammals, including humans, when errors occur that result in polyploidy?
  4. What percentage of flowering plants are polyploid?
  5. Why does Jennifer Frazier speculate that plants may be more tolerant of polyploidy than mammals?

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