A gene is a hereditary unit and part of a chromosome which carries a single instruction for characteristic of living cells; therefore, chromosomes carry the inherited information and control cell functions. Genes essentially consist of DNA.

DNA is a genetic material and is located within chromosomes, which are in the nucleus of every cell. Every DNA consists of :
A phosphate group
A sugar, deoxyribose
A base - adenine, guanine, thymine, cytosine

Replication of a DNA is when genetic material makes exact copies of itself; it occurs between cell divisions. It is said to be semi-conservative because when the 2 strands of the double helix separate, the strands are ‘zipped up’ by an enzyme, resulting in 2 new DNA molecules, each consisting of one ‘old’ strand and one ‘new’ strand. Replication of DNA requires proteins.

Proteins are vital substances because every organic chemical in a cell is either a protein or made by an enzyme, and enzymes can be proteins. The building blocks of proteins are amino acids.

Body cells are called somatic cells; which include the skin, liver, muscle, stomach and other body cells.

A mutation is a transmissible permanent change in DNA sequence. It can be an insertion or deletion of genetic information, or an alteration of the original genetic material.

Alleles are alternative genes; it can either be dominant or recessive.

Homologous - pair of chromosomes that are the same shape and size; one from each parent

Mitosis - part of growth and is concerned with the number of genetically identical cells; it results in no change in chromosome number. Mitosis occurs in:
Early human development (embryo): occurs throughout body by eventually get restricted by places e.g. bone marrow, skin, base of hair and nails
Multicellular organisms: repair and growth
Single celled organisms: sexual reproduction

Meiosis - only occurs in sex organs and results in change from diploid to haploid no. of chromosomes:-
Only occur in mature organisms
Produces gametes

Genotype - genetic composition of an individual

Phenotype - appearance/characteristic of an individual

Incomplete dominance
Homozygous blue bird mates with homozygous yellow bird (not dominant or recessive to each other)
Results in a mixture/blend of characteristics

Co - dominance
Gene A from one parent and gene B from the other (resulting blood type is AB)
Blood has features of both A type blood and B type blood and not a blend of the 2

Biotechnology - using technological facts and principles to create products and perform tasks for human beings

Cloning is the replication of an organism that is an exact genetic replica of another; for example, Dolly the Sheep was cloned from the breast cell of an ewe