Molecular genetics

• The DNA double helix is held together by hydrogen bonds between complementary base pairs.
• DNA stands for Deoxyribonucleic Acid
• DNA acts as a recipe for living things, providing a code for making proteins within a cell
• All living organisms have the same DNA structure and function
• In Eukaryotic cells, DNA is found in the Nucleus
• Eukaryotic cells, like plant and animal cells, contain DNA in a nucleus
• The DNA in eukaryotic cells is found as multiple linear chromosomes in the nucleus of the cell
• The nucleus is surrounded by a membrane
• DNA in prokaryotic cells, such as bacteria, is found free-floating in the cytoplasm because prokaryotic cells do not have a nucleus
• The DNA in prokaryotic cells is found as one large circular chromosome which contains the genes necessary for life processes
• Bacteria also have several small extra rings of DNA called plasmids which contain genes that give an advantage, such as antibiotic resistance
• DNA looks like a twisted ladder
• The sides of the ladder are made up of chains of sugar and phosphate units
• The steps of the ladder are made up of special molecules called Nitrogen Bases
• The ladder is called a Double Helix shape
• There are 4 different types of Nitrogen Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
• The chemical structure of each base means that it can only match up with one other base, following the complimentary base pair rule
• Adenine (A) only matches with Thymine (T)
• Cytosine (C) only matches with Guanine (G)
• Nucleotides consist of 1 sugar, 1 phosphate, and 1 base, and each one is called a Nucleotide
• Nucleotides join in any order to make DNA, as long as the bases match with their partner
• Chromosomes are long threadlike structures made up of DNA wrapped around proteins
• Chromosome numbers vary considerably among different organisms
• More complex organisms have a greater number of chromosomes
• A gene is a coding segment of DNA that codes for making a protein
• A single chromosome may contain hundreds of genes
• Human beings are 99.9% genetically identical to each other
• We share 98% of our genes with chimpanzees
• 50% of our genes are the same as cabbages
• Genes come from both your mother and your father
• The mix of genes you end up with is random, explaining why siblings can look different but still be similar
• A karyotype is a representation of the chromosomes present in the somatic (body) cells of an organism, ordered in pairs from largest to smallest
• A karyotype can show:

  • The number of chromosomes in each cell
  • The sex of a person
  • If there is a chromosome abnormality (e.g. an extra chromosome or missing a chromosome)
• The other 22 pairs of chromosomes are called autosomes
• The sex chromosomes in females are XX and in males XY
• A fly has 4 pairs of chromosomes
• The karyotype of a ring-tail possum can determine if it is a male or female
• Human karyotypes can show chromosomal abnormalities
• Identify abnormalities in each karyotype
• DNA is the genetic material inherited from parents