InThinking Revision Sites

INTHINKING REVISION SITES

Own your learning

Why not also try our independent learning self-study & revision websites for students?

We currenly offer the following DP Sites: Biology, Chemistry, English A Lang & Lit, Maths A&A, Maths A&I, Physics, Spanish B

"The site is great for revising the basic understandings of each topic quickly. Especially since you are able to test yourself at the end of each page and easily see where yo need to improve."

"It is life saving... I am passing IB because of this site!"

Basic (limited access) subscriptions are FREE. Check them out at:

www.StudyIB.net

Polyploidy

  • /
  • Additional HL/
  • HL Genetics Activities for Learning/
  • Polyploidy

Polyploidy in Allium and in other Crop plants

Using the examples of agricultural crop plants students learn what polyploidy is and how it helps solve the problems of hybrid infertility in plants often leading to new species and hybrid vigour. There are data analysis style questions about an interesting research paper looking at mechanisms of polyploidy in a species of Allium called "Japanese bunching onion"

Lesson Description

Guiding Question

How can polyploidy produce better crops?

How does polyploidy lead to a new species of plant?

Activity 1 - What is polyploidy?

Watch this short video from the Florida museum of natural history

Answer the following questions about polyploidy after watching the video.

Questions

  1. What is polyploidy?

  2. Why does polyploidy lead to fertile organisms, unlike the infertility we see in hybrid animals like mules?
    (where chromosomes don't pair properly in the gametes of mules)

  3. Name three examples of polyploid crop plants mentioned in the video.
  4. What advantage has polyploidy been thought to give to crop plants?
  5. What other species are mentioned in which polyploidy has played a role in genome evolution?

Click the eye icon to display some 'model answers'

Model answers

  1. Polyploid is "an organism with more than two sets of chromosomes"
  2. A polyploid plant can have, for example, four sets of chromosmes = tetraploid.
    Therefore the cells have pairs of chromosomes (in the two whole diploid sets) so gametes can be produced normally in meiosis. The homologous chromosomes pair up normally in metaphase I of meiosis.
    After meiosis, each gamete has one copy of every chromosome. 
    This is unlike mules (with 63 chromosomes)  that can't corectly form homologous pairs. So many gametes are missing chromosomes.
  3. Wheat, Corn / Maize, and Brocoli are examples of polyploid crop plants
  4. Advantages of polyploid crops are increased size, or increased yield.
  5. Vertebrates, Sunflowers and many other species.

Activity 2 - Data analysis of polyploidy in Allium fistulosum

Once the basic principals of polyploidy are understood consider the research results in the polyploidy and speciation data analysis questions worksheet

There are Data analysis & polyploidy model answers on this separate page.

Activity 3 - Plenary - speciation by polyploidy. (Stepping stones)

This is a class activity to help everyone to learn the details of the stages and to give students an opportunity to ask about things they don't understand in a discrete way.

Instructions

  1. Print the A4 stepping stones:  Explaining speciation by polyploidy
  2. Lay them on the floor of the lab .
  3. Students have to step onto the first stone and explain which part of the process the word on the stone represents.
  4. Only when the answer is correct can they step onto the next stone.
  5. The challenge is to step across all the stones, explaining each of the words one step at a time until the student crosses all the stones.

Variations

This could be a class challenge, the whole class could help a volunteer to explain each of the steps and cross the stepping stones.

For more excitement there could be a pot of sweets for the volunteer to collect at the end of the stepping stones.

The volunteer could (should) retrace their steps with the sweets and describe the steps backwards of course!

At the end of the lesson the stepping stones could lead students towards the door of the room - they could be obliged to explain the steps individually before leaving the lesson.

Teachers notes

These activities will take about 1 hour.

The first activity is a simple introduction to polyploidy.

The data analysis questions have been written from data taken from quite a complex biological paper and they have been simplified so that they fit the IB biology guide more closely.  One or two of the questions refer to earlier genetics topics, eg. karyograms, and meiosis.

The final activity focuses on the way that polyploidy can lead to rapid speciation through reproductive isolation, as plants with very different chromosome numbers are likely to produce infertile hybrids.  This may require some teaching before students are confident to explain the steps on their own. There are also other ways to describe this process.

Polyploidy does occur in some animal species but it is much more common in plant species, and plant breeders have promoted polyploidy in the development of new agricultural crops over many years.