Genetrix genetics

What is genetics?

The science of Genetics is basically the study of two things:

1. What controls the appearance and other characteristics of living things.
2. How characteristics are passed down from parents to their offspring.

Genes

Genes are the things inside of organisms that control their characteristics.


Where are they?

All living things are made up of one or more cells.

Each cell has a control centre called the nucleus.

In each nucleus there are a number of long thin threads called chromosomes.

Chromosomes contain DNA and protein molecules.

The DNA core of a chromosome has a structure like a long twisted ladder.

One gene is one relatively short part of a chromosome.

The DNA on one chromosome could have as many as 1000 genes along its length (but there would also be lots of DNA that isn't actually genes).

How do you see these cells and chromosomes?

You may have done this already in school. First you scrape some cells from the inside of your cheek. (To see more, put the cursor arrow on pictures and wait a few seconds)

Then you put them on a slide, stain them,

then gently lower a coverslip onto them

Finally you can look at your cells through a microscope

The darker stained ovals in the cells are the nuclei. The chromosomes are all unwound and tangled together so you can't see them individually.

Did you Know?

You are made up of somewhere between 10,000,000,000,000 (ten trillion) to 100,000,000,000,000 (100 trillion) cells!

There are about 200 different types of cells which have a weird and wonderful range of shapes and sizes.

Each type carries out a different job. For example:

Red blood cells carry oxygen

Nerve cells carry electric signals around the body

Muscle cells help you move.

All human cells (with a few exceptions) have a nucleus with 46 chromosomes.Overall we have about 20,000 to 25,000 different genes but we have two copies of each gene.

Each of our cells has about 2metres of DNA in it! 2m - how does it fit in? DNA molecules are very, very thin and can be coiled up very tightly, coils upon coils.

The DNA in your whole body could stretch to the sun and back about 50 times!

From chromosomes to genes

The diagram which follows is to show you how DNA can tightly coil up so that the two sides of a chromosome (which are exact copies of each other) can be pulled apart during cell division. In this way each new cell gets a full copy of your entire set of genes.

	This is a diagram of a chromosome that is largely coiled up. The lower arm is shown in greater detail to show it is looped.
	This area has been magnified more to show that the chromosome is coiled up. Note that it has coils made of already coiled chromosome. There is a coating of proteins over the DNA. These proteins are involved in controlling genes.
	Greater magnification and more uncoiling shows that the thin strand of DNA is wrapped around units which are a protein called histone.
	Finally, with even greater magnification we see the DNA. Its structure looks like a twisted ladder. The "rungs" of the ladder are made of pairs of "bases". There are only four different bases. Their names are symbolised by the letters A, T, C and G. Note that A is always paired with T, and C pairs with G. It is these bases that carry the genetic code. One gene consists of several base pairs (bp). The shortest genes known are about 60 bp, but most genes have hundreds or even thousands of bp.

(Please note that the diagram above is just a diagram, it does not show the exact appearance of DNA and Chromosomes.)

To learn more about genetics, go to the next page