IB Genetics 2013: Topic 4 (SL and HL)

1. IB Genetics 2013: Topic 4 (SL and HL)

2. Welcome to genetics!

3. Welcome to genetics! • September 2012

4. Genetics: The science of difference The science of heredity - the ‘genetic properties’ or inherited features of an organism • Molecular genetics: study of structure and function of DNA and RNA • Population genetics: study of genes within populations, including gene frequency, the gene pool and evolution

5. Essential definitions of genetics

6. THE GENOME ‘The entire genetic information of an organism’: the entire set of genetic instructions • The genome • the announcement • What have we got from the genome?

7. The gene • IB: ‘a heritable factor that controls a specific characteristic’ • Heritable – passed on through the generations • Factor – locatable sequence of nucleic acid (DNA) • Characteristic – ‘genetic traits’ • an illustration

8. Some numbers… • How many bases in the human genome? • By how many bases do each of us differ? • How many genes do we have? (less than we thought!) • How much of our DNA consists of protein-coding genes? • What does the rest of the DNA do? • Do all genes code for protein? • Are all of our genes in the nucleus? • What does the rest of the DNA do? • Do all genes code for protein? • Are all of our genes in the nucleus?

9. Genes are located in chromosomes • ‘coloured bodies’ • Eukaryotic chromosomes consist of DNA wound around histone proteins • Constriction point: centromere • When are chromosomes visible in the cell?A fly-over Chromosome 11...

10. Gene Locus • The specific position of a gene on a chromosome • All individuals of a species will have the same gene at the same locus on the same chromosome • In other words, they are homologous

11. Diploid/ haploid

12. Diploid/ haploid Diploid Haploid Gametes (sperm and egg cells) Contain haploid number of chromosomes – only one of each chromosome Human haploid number is 23 • Cells/organisms with paired chromosomes • Sexually reproducing organisms are diploid • All eukaryotic cells with exception of gametes • Contain 2n chromosomes, one of each pair from each parent • Human diploid number is 46, i.e. 23 pairs of ‘homologous’ chromosomes

13. Number of chromosomes Zea Mays Homo Sapiens Musmusculis

17. Homologous chromosomes • ‘similar in shape and size’ • Carry the same genes (not necessarily the same alleles for that gene) • NOT identical

18. Essential definitions: homologous chromosomes • Human somatic cells have 22 homologous chromosome pairs (autosomes) and one non-homologous pair (sex chromosomes) • One maternal/ one paternal • Same size and structure • Same genes at same loci (not necessarily the same alleles for that gene) • NOT identical

19. Identifying chromosomes (karyotyping) Chromosomes are lined up in their homologous pairs according to: • Size (1 largest – 22 smallest) • Shape – position of the centromere • Specific banding (staining) patterns using dyes (Giemsa) More later! • and in more detail here

20. Allele ‘One specific form of a gene, differing from other alleles by only a few bases and occupying the same gene locus as other alleles of the gene’ ‘Alternative’ versions of a gene At the same gene locus

21. Alleles

22. Some ‘celebrity genes’ • BRAC1 and 2

23. Celebrity genes (2) Mutations in the CTFR gene cause cystic fibrosis

24. Celebrity genes (3) APOE4 increases the risk of Alzheimer’s Disease

25. Celebrity genes (4): the oBLeptin gene • Encodes a protein that plays a major role in regulation of body mass and other hormonal functions. • Abnormalities in the Leptin gene are associated with some types of obesity

26. Mutation The basis of all genetics ‘… the fuel for the Darwinian factory’ ‘Rarely pure and never simple’

27. Gene mutation • Definition: A random change in genetic material • ‘COPYING ERRORS’ OF DNA • Various types of mutation – base substitution, insertion, deletion • (point, frameshift – not required by IB) ‘Mutation is the destroyer and creator of life’ ‘Thanks to mutation, we’re not all still in the primordial soup’

28. Not all mutations cause disease • ?silent mutations • We have two copies of each gene – the functional homologous chromosome may take over or ‘compensate’

29. Causes of mutation (1) • Copying error during DNA replication (error made by DNA polymerase and not corrected by the DNA repair enzymes) • Intra-cellular mutagenic chemicals (free radical molecules) • ?Gamma radiation?....

30. Causes of mutation (2) • Radiation • Chemicals • Viruses • Diet • Stress • Lifestyle ‘Hiroshima – the most cynical Biology experiment of all time’

31. Types of mutation here's an animated summary...

35. Sickle Cell Anaemia – inherited base substitution mutation

36. 5% of the world’s population carry the sickle cell gene Sickle cell Hb makes the RBC collapse inwards An introduction to sickle cell disease

38. Life with sickle cell anaemia • Shortened RBC lifespan – 16 days (instead of 35) • Causes high mortality in newborn • Reduces lifespan by average of 30 years if untreated • Low red cell count (anaemia) • Abnormal red blood cells stick in blood vessels – stroke, jaundice, organ failure, lung damage, chronic pain • Even ‘carriers’ with only one copy of the gene have mild sublinical effects

39. Sickle Cell anaemia – Base substitution mutation • Base substitution (point) mutation on chromosome 11 • Inherited during conception (‘germ cell mutation’) • GAG becomes GTG • Valine replaces glutamic acid • HbS (sickle cell Hb) instead of HbA (normal adult Hb) • From the DNA learning centre • chromosome 11 flyover

40. A walk through sickle cell disease

44. ‘Mutation is the fuel for the Darwinian factory’

45. Map of malaria prevalence 1920

46. Map of sickle cell allele prevalence in Africa • Berkeley Uni link • The power of evolution

47. Homework: Deepening your knowledge on sickle cell anaemia • Q. 10 – 15 in your worksheet Links on Sickle-cell anaemia are on the Blog, in the Genetics Section

48. ‘Like begets like’…