 4.1.1: State that eukaryotic chromosomes are made of DNA and proteins  4.1.2: Define gene, allele and genome  4.1.3: Define gene mutations  4.1.4: Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle cell anaemia

 Chromosomes are bundles of long strands of DNA › If you could unwind a chromosome, it would be like unraveling a ball of string  In eukaryotes that reproduce sexually, chromosomes always come in pairs › Humans have 46 chromosomes in 23 pairs › The DNA un eukaryotes is associated with proteins which helps to keep the DNA organized

 A gene is a heritable factor that controls a specific characteristic › Heritable means passed on from parent to offspring and characteristic refers to genetic traits such as your hair color or your blood type › The estimated 30,000 genes which you possess are organized into chromosomes

 The genes which determine eye color have more than one form › Variations (like in eye color) of a gene are called alleles  An allele is one specific form of a gene, differing from other alleles by one or a few bases  Alleles of the same gene occupy a corresponding place (locus) on each chromosome of a pair

 In order to find out which gene does what, a list must be made showing the order of all the letters in the DNA code (sequence of bases) › A complete set of an organism’s base sequence is called its genome › The complete genome of a few organisms have been fully written out.

 A mutation is a random, rare change in genetic materials › One type involves a change of the sequence of bases of DNA  If DNA replication works correctly, this should not happen

 Base substitution mutation › The consequence of changing one base could means that a different amino acid is placed in the growing polypeptide chain  This may have little or no effect on the organisms or it may have a major influence on the organisms physical characteristics  hill.com/sites/ /student_view0/chap ter15/mutation_by_base_substitution.html hill.com/sites/ /student_view0/chap ter15/mutation_by_base_substitution.html

 In fruit flies › One base substitution mutation can cause:  Extra pair of wings  Change in eye color  The number of legs  Shape of the wings

 In humans: › one base substitution mutation can cause:  Mutations is sometimes found in the gene which creates hemoglobin for red blood cells  This mutation gives a different shape to the hemoglobin molecule  The mutated red blood cell with the characteristic curved shape made its discoverers think of a sickle (a curved knife used to cut tall plants)  Called sickle cell anaemia

 Sickle cell anemia › One base is substituted for another so that the codon GAG becomes GTG › During translation instead of adding glutamic acid it added valine instead  This results in a different shape of the polypeptide— hemoglobin molecule has a different shape which causes the red blood cell have a different shape

 Symptoms of sickle cell anemia › Weakness, fatigue, and shortness of breath › Oxygen cannot be carried as efficiently by the irregularly-shaped red blood cells › Hemoglobin tends to crystallize within the red blood cells, causing them to be less flexible  The affected red blood cells can get stuck in capillaries so blood flow can be slowed or blocked

 People affected by sickle cell anima have a risk of passing the mutated gene to their offspring › Mutated gene is mostly found in populations originating from West Africa or from the Mediterranean