GENETICS

Recap & Basics

DNA

• Structure

• Function

• Replication

Structure of DNA

•Deoxyribose sugars joined by Phosphate bonds

•Bases – A, T, C, G bonded to sugars

•Two corresponding strands are joined together by weak bonds between bases

(A & T; C & G)

•Twisted into a double helix

Function of DNA

• Carries the genetic code for functioning of an organism

• The sequence of bases on one strand contains the genetic code for all proteins needed by an organism

• Three bases = a triplet; one triplet codes for one amino acid (protein is made up of chains of amino acids).

• Groups of triplets code for a protein = a gene.(gene is section of DNA that codes for a protein)

Packaging of DNA

• There is a lot of DNA in cells, especially in eukaryotes.

• It has to be wound around proteins to make it fit into the cell.

• Usually DNA occurs as chromatin fibres within cells.

• Before replication, chromatin fibres condense to form chromosomes.

Replication of DNA

• DNA in cells replicates itself before cell division.

• Mitosis: cell division for growth and repair

• Meiosis: cell division for sexual reproduction

• Cell division

Chromosomes

• In somatic cells, chromosomes exist in homologous pairs (one from father and one from mother).

• Humans have 23 pairs – so 46 chromosomes.

• One half of the pairs is a set called the haploid number, n. Two sets are diploid, 2n.

• In gametes (egg & sperm) there is only a haploid number of chromosomes.

Genes• Genome is the total amount of genetic material

an individual has.

• One gene codes for one protein.

• It is possible to have variations of the same protein. These arise from variation of the same gene.

• Different varieties of the same gene are called alleles.