B1- You and Your Genes:

Genes, Chromosomes and DNA...

1. Most of the cells in the human body have a nucleus, this is where the genetic material is. Genetic material is organised into Chromosomes  (humans have 23 pairs of chromosomes in each cell). Each Chromosome is one long chain of DNA, coiled up. A gene is a short length of a chromosome. Genes control the development of different characteristics for example your hair colour.

What do Genes do?

Each gene is a code for making a certain protein, which is what makes up cells.

Some proteins are structural, meaning they make up parts of the human body such as the hair, skin or blood. An example of this is collagen which is found in tendons, bone and cartilage.

Functional Proteins, have a function in the human body. For example amylase is a digestive enzyme that breaks down starch.

Genotype= all the genes an organism has.

Phenotype= the characteristics an organism displays

Some characteristics are only controlled by genes such as dimples. On the other hand some are only controlled by environmental factors such as where you live. Some are controlled by both; such as weight.

Sperm and Egg Cells:

In BODY cells chromosomes come in pairs, one from each parent. However, in Sex cells there are only 23 single chromosomes, this is because when the egg is fertilities by the the sperm the two sets of 23 single chromosomes will join to make the complete 46, like any other body cell has.

Alleles= different versions of the same gene.

Why aren't siblings identical to each other and their parents?

A child gets half of their genes from each parent, meaning they will get half of their alleles from their mum and half from their dad, this is why the child will not look identical to either parent. In addition, there are millions of combinations of alleles, meaning no two children look the same except identical twins.

Combinations of alleles:

If you're homozygous for a trait you have 2 of the same alleles for that particular gene. If you're heterozygous that means you have 2 different alleles for the trait,

Alleles can be dominant or recessive, a dominant allele will overpower a recessive allele. In order to show the recessive characteristic you need both alleles to be recessive, (the capital letter in genetic diagram is dominant and the lower case is recessive.)

Male or Female?

The 23rd pair of chromosomes in human body cell is labelled XY. These are the sex chromosomes and decide whether you will become male or female. Men have both an X and a Y chromosome, it is the Y chromosome which causes male characteristics. All women have two X chromosomes; it is a lack of Y chromosome which causes female characteristics to develop.

The gene that causes male characteristics is specific protein which causes testes to grow instead of ovaries when the embryo's…