Genes and Varitaion

The genome is the entire genetic material of an organism

The genetic material is arranged in chromosomes

A gene is a short length of a chromosome as they determine the production of proteins

This controls the development of different characteristics

An organism phenotype changes so the characteristics displayed are different

Continous Variation - Characteristics that can only take a range of different values

Discontinuous Variation - Characteristics that can only take set number of forms 

Environmental Variation - A shift in external conditions caused by human activity

Genetic Variation - The product of meiosis, mutation and sexual reproduction that leas to changes in our genome

A mutation is a random change in an organisms DNA that can be inherited

The sequence of DNA bases in the gene is changed which produces a genetic variant

Most genetic variants have little effect on the protein, and there may not be an effect on the phenotype

Some variants have a small influence for example eye colour, and some have a large influence like cystic fibrosis 

Coding DNA - Mutations in coding DNA affects the proteins and the way they function, for example in enzymes

Non - Coding DNA - Mutations in non- coding DNA affect how genes are expressed. They can stop the transcription of mRNA so the protein is not produced at all

Sexual reproduction is where genetic information from two organisms combine to produce genetically different offspring

Gametes (sex cells) contain half the number of chromosomes of a normal cell - they are a haploid

A diploid is created as a male gamete fertilises a female gamete

The fertilised egg then undergoes mitosis and develops into an embryo

Gametes are created by meiosis and don't produce identical cells

It only happens in the reproductive organs and produces four haploid gametes after two divisions

Gene - controls the characteristic

Phenotype - the gene that is expressed

Allele - different form of a gene

Genotype - the alleles for a gene

Recessive - small letter, both have to be small letter to be expressed

Dominant - capital letter, only one needed to be expressed

Homozygous - the same allele twice

Heterozygous -  two different alleles