Most phenotypic features are the result of multiple genes acting together, and not single genes. For example, as many as 16 genes are thought to be responsible for human eye colour.
Genetic variation
Different characteristics can arise as a result of both random mutation and sexual reproduction. Random mutation occurs in gametes to produce offspring with 'brand new' phenotypic characteristics, whereas sexual reproduction causes the offspring to have a new combination of characteristics from both its mother, and its father.
Environmental variation
Characteristics can also be caused by an organism's environment, but these changes are generally not heritable (there is no change in the DNA of the organism). For example, a child who does not receive adequate nutrition will not grow to their full height, however this has no effect on their potential height as determined by their genetics.
Sexual reproduction
1. Joining of male and female gametes, each containing genetic information from the mother or father
2. Gametes are formed by meiosis, as they are non identical
3. A normal cell has 46 chromosomes, with two sets of 23 chromosomes (one from each parent)
4. Genetic information from each parent is mixed, producing variation in the offspring
Asexual reproduction
1. One parent with no gametes joining
2. Happens using the process of mitosis, where two identical cells are formed from one cell
3. No mixing of genetic information
4. Leads to clones, which are genetically identical to each other and the parent
Organisms that reproduce asexually
Bacteria
Some plants
Some animals
Advantages of sexual reproduction
Produces variation in offspring
Decreases chance of whole species becoming extinct
Allows selective breeding
Advantages of asexual reproduction
Only one parent is needed
Uses less energy and is faster as organisms do not need to find a mate
DNA
Chemical that contains genetic material, made up of nucleotides with a sugar, phosphate and one of four organic bases (A, C, G, T)
Double helix
Structure of DNA, with two strands twisted around each other
Gene
Short section of DNA that codes for many amino acids, which are joined together to make a specific protein
Genome
All the genetic information (DNA) of a single organism
Protein synthesis
DNA contains genetic code, mRNA is made as a template, mRNA moves to ribosomes, amino acids are brought by tRNA and joined to form a polypeptide, which then folds into a 3D protein structure
Genetic variants
Small changes in the order of bases that make up a strand of DNA, can affect the structure of proteins
Genotype
The genes present in the DNA of an individual
Phenotype
The visible effects of those genes (e.g the proteins that they code for)
Mutations
Changes the sequences of bases in DNA, can insert, delete or substitute bases
Most mutations do not alter the protein or only do so slightly, but some can have a serious effect and change the shape of the protein
Monohybrid inheritance
Using a Punnett square to determine the probability of offspring having certain genotypes and phenotypes based on the alleles of the parents