Crop Circle Genetics

This year's exhibit described on information boards how circular genetic maps help scientists to find their way through the genetics of the cereals.

Information Board 1

Can complicated maps make biology easier?

Rice, wheat and maize have a common ancestor and so contain many similar genes, but 100 million years of evolution has resulted in very different plants.

Rice contains about 40,000 genes and is, genetically, one of the simplest cereals. Wheat and maize are far more complex. They have more genes embedded in a great deal more DNA (the chemical basis of genes) that does not encode genetic information. In fact wheat contains 40 times as much DNA as rice.

When studying the genetics and biology of the cereals it is often easier to use the relatively simple rice plant than the other cereals. The genetic similarities allow information from rice to be used to understand similar aspects of wheat and maize biology.

On our map, genes altering pigment, ligule production and plant height, are in equivalent regions of the different maps.

Information Board 2

How Crop Circle Genetic maps work.

The genetic maps of the cereals are arranged in concentric circles. The map of the simplest cereal (rice) in the centre and that of the most complex (wheat) is on the outside. The rice map is divided into 12 chromosomes (these are naturally occurring blocks of genes).

We have organised the genetic maps of the other cereals so that pieces of the map that carry the same information are in the same sector of the circle and are aligned with the rice chromosome that also carries the same information.

During evolution blocks of genes have moved around and equivalent genes no longer appear in the same place in the genetic maps of the different cereals.

The arrows on our circular maps show where particular blocks of genes have moved to. On the wheat map you can follow the changes that have occurred by connecting the blocks in number order.

The maps on display have triangles, crosses, numbers, and letters on them. To find out what they mean look at the handout entitled "Understanding Crop Circle Genetics".

Information Board 3

Genes in common.

Despite their external differences cereal plants have many genes in common because they share a common ancestor. Our understanding of how evolution has shuffled blocks of genes around means we know where to look for interesting genes in the different cereal species.

This exhibit shows how the same kinds of variation in gene activity can be found in genes common to wheat, rice and maize. These genes are located in similar regions of the maps of all three species.

1. A gene for red pigment production. The activity of the gene causes red/purple stem colour. In plants where the activity of the gene is reduced (or switched off) the stem is a ‘normal’ green colour.

2. A gene that controls the production of the ligule. The ligule is the small protrusion at the base of the leaf, which clasps the stem. A mutation in this gene results in ligueless plants.

3. A gene that controls the plant’s response to a natural plant growth hormone. When the plant produces this growth hormone the cells in the stem respond by elongating. A mutation in this gene prevents the stem cells responding so they do not elongate, the plant stem remains short resulting in dwarf plants. Although the gene is present, the dwarfing mutation has not yet been identified in rice).

Information board 4

Crop Circle Genetic maps and evolution.

Cereal crops are our major food source. Rice alone is the staple food of over 50% of the world’s population, so understanding the biology and genetics of cereal plants is not just of academic interest.

Rice, maize and wheat look rather different from one another, but at the level of their genetics, they, and other cereals, are very similar. Not only do the cereals have many genes in common, these genes are organised in similar ways.

Genes are organised like beads on a string so it is possible to make linear or circular maps that show the location of genes in relation to one another. Our circular genetic maps have helped us to understand how, during evolution of the different cereals, large blocks of genes have been reorganised and moved around.

The arrows on our maps show where particular blocks of genes have moved to. On the wheat map you can see the changes that have occurred by connecting the blocks in number order.

The maps are a useful way for us to visualise the relationships between the cereals and so share biological information across the species.