A gene is a length of DNA which codes for a single characteristics or trait we inherit from our parents. Genes control every aspect of our body and how it works. Each characteristic has its own gene.
Genes are found in chromosomes which are found in the nucleus of our cells. Chromosomes are coiled up lengths of DNA each carrying lots of genes.
Remember – chromosomes are made of DNA and genes are short sections of DNA.
How many chromosomes do humans have?
Human cells have 46 chromosomes, these are found in pairs. In each pair one is inherited from each parent. This means offspring have a combination of both parents characteristics. This is called inherited variation.
Dominant and recessive genes
Genes can be dominant or recessive, the dominant gene is the one that is shown in the phenotype of an organism ( observable characteristics ). For example, brown eye colour is dominant over blue, so if a person has one blue eye gene and one brown eye gene they will have brown eyes as it is the dominant gene that is expressed. Different versions of the same gene are called alleles.
What is variation
Variation refers to differences between organisms. Some differences are visibly obvious such as hair and eye colour, others are not obvious such as blood type.
Continuous variation refers to variation of things that can have a range of values, such as height and weight.
Discontinuous variation is where characteristics can only have a certain value. For example blood group and eye colour.
What about the environment?
The environment also plays a role in how a person looks, how healthy they are and other factors. For example, if a person has genes that make them athletic wouldn’t reach their full potential if they were undernourished or lived in an area with high levels of air pollution. Almost all characteristics are affected by both genetic and environmental factors.
Genes are not just for humans
Plants also inherit characteristics from the parent plant via genes. Plants are also affected by environmental factors, for example a plant with genes to grow tall won’t grow well in the dark or in poor soil even with genes that predispose it to height.
Learn more about DNA with my candy DNA model.
I also have a fact sheet where you can learn about Rosalind Franklin and her research into the double helix structure of DNA.
What are base pairs?
DNA is made from nucleotides. There are four different nucleotides:
We call these bases and usually to them by the first letter of their name.
A pairs with T and G with C.
One way to illustrate this is to thread different beads on pipe cleaners to show that the two sets of pairs always pair together.