1. 3.1 Genes Understanding: -A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic -A gene occupies a specific position on one type of chromosome -The various specific forms of a gene are alleles -Alleles differ from each other by one or a few bases only -New alleles are formed by mutation -The genome is the whole of the genetic information of an organism -The entire base sequence of human genes was sequenced in the Human Genome Project Applications: -The causes of sickle cell anemia, including a base substitution mutation, a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin -Comparison of the number of genes in humans with other species Skills: -Use of a database to determine differences in the base sequence of a gene in two species Nature of science: -Developments in scientific research follow improvements in technology: gene sequencers, essentially lasers and optical detectors, are used for the sequencing of genes

2. Genes Heritable factor that consists of a length of DNA and influences a specific characteristic Occupies a specific position on one type of chromosome (locus)

3. Alleles Various forms of genes Dominant allele shown (in this case brown hair) Slight variations in base sequences

4. Mutations New alleles formed from other alleles (random) Most common: base substitution Usually neutral or harmful

5. Mutations New alleles formed from other alleles (random) Most common: base substitution Usually neutral or harmful

6. Mutations New alleles formed from other alleles (random) Most common: base substitution Usually neutral or harmful

7. Mutations New alleles formed from other alleles (random) Most common: base substitution Usually neutral or harmful

8. Mutations New alleles formed from other alleles (random) Most common: base substitution Usually neutral or harmful

9. Sickle cell anaemia Mutations can cause genetic disease Most common genetic disease in the world Inherited if mutation occurs in a cell of the ovary or testis that develops into an egg or sperm

10. Sickle cell anaemia Mutation of Hb gene that codes for a polypeptide in haemoglobin Most humans have HbA. Base substitution mutation converts SIXTH CODON of the gene from GAG to GTG it forms Hbs

11. Produces valine instead of glutamic acid Causes haemoglobin to stick together in low oxygen levels

12. Lungs High oxygen levels = normal RBC Tissues/muscles Low oxygen levels = sickle cell shape The result: Block blood flow RBCs die quickly – cannot be reproduced quick enough = anemia

13. Sickle cell anaemia Cause:Symptoms:Normal RBC: Sickle cell RBC: Why is this shape a problem?

14. Genome All of the genetic information of an organism Humans: -46 molecules that form chromosomes -DNA in mitochondria Plants: -DNA in chromosomes -DNA in mitochondria and chloroplasts

15. Human Genome Project Entire base sequence of human genes sequenced Started: 1990 Complete sequence: 2003 A human genome not THE human genome Majority of base sequences all shared – very small differences cause diversity How many genes does a human have? Is it more or less than a water flea? A tree?

16. Numbers of genes Larger or more complex organism doesn’t necessarily mean it has more genes: Gut bacteria: 1,700 genes Large tree: 46,000 genes Human: 23,000 genes Water flea: 31,000 genes Rice: 41,000 genes

17. Comparing genes Use the database to determine differences in base sequences of two species Follow the instructions on page 144 to compare different species