Chromosomes are made up of DNA
The chromosomes carry genes along them
Genes code for proteins
DNA is a triplet code; 3 bases = one amino acid
Some bases are stop/start, otherwise nonsense (don't code for anything we know)
Sequence of bases determines the protein produced - which gives the characteristic/trait
Small differences in the DNA sequence of a gene = alleles result by mutation

DNA is a complex chemical that carries genetic information. DNA Is contained in chromosomes, which are found in the nucleus of most cells. The gene is the unit of inheritance and different forms of the same genes are called alleles.

Chromosomes

Chromosomes are x-shaped objects found in the nucleus of most cells. They consist of long strands of deoxyribonucleic acid, or DNA for short. A section of DNA that has the genetic code for making a particular protein is called a gene.

The gene is the unit of inheritance, and each chromosome has several thousand genes. We inherit particular chromosomes through the egg of our mother and sperm from our father. The genes on those chromosomes carry the code that determines our physical characteristics, which are a combination of our two parents.

The bases in the DNA molecule carry the different codes needed for different amino acids. The code for a particular amino acid is made from three bases in a particular order.

The backbone of the DNA molecule consists of two strands of alternating chemical strands of alternating sugar molecules and phosphate groups, the two strands twisted to form a double helix. Each sugar molecule is attached to one of the 4 bases called adenine, guanine, thymine and cytosine (A, G, T, C for short) The bases are paired up on opposite strands. A is always paired with T, and G is always paired up with C. This is called complementary base pairing - the order of bases in one strand determine the order of bases in another. A nucleotide is a basic building block for DNA made up of phosphate, sugar and base. The two strands are held together by weak hydrogen bonds. A gene consists of hundreds or thousands of bases. A gene codes for a particular protein by its particular base sequence.

DNA must copy or replicate itself before any cell division can take place. The DNA Double Helix is perfectly suited for replication because each strand can serve as a template to produce a strand opposite to itself.

First it is "unzipped" - the two strands are separated. New nucleotides in the cell line up alongside the unpaired bases, A pairing with T and G pairing with C. The new nucleotides are joined together using an enzyme called DNA polymerase.

DNA replication is semi conservative i.e. each strand in the original DNA molecule is used as a template o make a new strand of DNA. Each new DNA molecule contains an original strand and a newly made strand.

	Created by Ambionne Wilson over 10 years ago

1 Science (Genetics) Note on 1.9 Genetic variation 2, created by Ambionne Wilson on 09/08/2014.

1.9 Genetic variation 2