Causes Of Variation
INTERSPECIFIC - differences between species
INTRASPECIFIC - differences within a species
Intraspecific variation is caused by genes and the environment
Characteristics caused by genes (genotype):
- eye colour, blood type etc...
These characteristics come from genes inherited from parents
Characteristics caused by environment (phenotype):
- weight, accent etc....
These are all caused by environmental factors and aren't inherited.
Drawing Conclusions About Cause Of Variation
In any population there is a lot of variation which can be caused by genes, environment, or both.
One thing that was originally thought to be an environmental characteristic, is now seen as a genetic one too.... OVEREATING
-At first people thought overeating was only caused by increased availability of food
- Eating releases dopamine which makes people stop eating, but one allele produces 30% less dopamine than another, so overeating can be caused by genes.
Another example of a mix between genes and environment is HEIGHT. Someone could have the genes to be six feet tall, but if they have the wrong diet, they could only grow to be five feet five inches.
DNA is made of a NUCLEOTIDE, a SUGAR, a BASE and a PHOSPHATE.
Two POLYNUCLEOTIDES (lots of nucleotides together) join to make a double helix. HYDROGEN bonds form between the bases and the SUGAR and PHOSPHATE creates the backbone of the structure.
DNA's structure makes it good at it's job. The molecules are COILED and SMALL so they can fit in smaller spaces such as the nucleus. The double helix also makes it a very stable cell and means it's good at self replication.
- Genes code for proteins (polypeptides)
- Proteins are made from amino acids, different proteins have a different order of amino acids
- The order of the bases in DNA, change what amino acid is made
- Each amino acid is coded for by a sequence of three bases in a gene (triplet)
- Genes exist in different forms such as ALLELES. These are different versions of one gene
- Gene mutations can result in non functioning proteins