1. Chapter 13 Raven & Johnson Chapter 15 Campbell Chromosomes & Inheritance

2. Mendel & Genes 1902 – Chromosomal Theory of Inheritance Genes have specific loci on chromosomes – chromosomes divide and move

4. Thomas Hunt Morgan’s Thomas Hunt Morgan’s work Drosophila melanogaster (fruit fly) Normal phenotype – wild type – red eyes Mutant phenotype – white eyes Discovered through mating that white eyes was sex linked Gene located on sex chromosome

5. Thomas Hunt Morgan’s Work

6. Thomas Hunt Morgan’s work If on X chromosome, females need two copies to express recessive gene Males need only one (they are XY) Females with one – carrier (can pass on)

7. Thomas Hunt Morgan’s work Linkage – genes close to each other tend to be inherited together

8. Genetic Recombination Production of offspring with new combinations of traits inherited from two parentsProduction of offspring with new combinations of traits inherited from two parents If unlinked, there is a 50% frequency of recombinationIf unlinked, there is a 50% frequency of recombination

9. Completely linked have no recombinants – 0% frequency If normally linked, then crossing over could break the linkage and raise the frequency

10. Genetic Mapping Alfred Sturtevant The farther apart two genes are on a chromosome, the more chances that crossing over can occur and the higher the recombinant frequency will be Can use frequency numbers to map the distance and order of genes – linkage map

11. Genetic Mapping Testcross design to map the relative position of three fruit fly genes, body color (b), wing size (vg), and eye color (cn). The recombination frequency between cn and b is 9%. The r.f. between cn and vg is 9.5%. The r.f. between b and vg is 17%.

12. Genetic Mapping The only possible arrangement  eye color gene between the other two Map unit – distance between genes (1 m.u. = 1% recombination frequency) Distances are added

14. Sex Chromosomes XX – female XY – male Determined by sperm (X or Y) Sex linked – usually on X & recessive Fathers pass to all daughters but no sons Mothers can pass to either

15. Sex Chromosomes Ex - colorblindnesscolorblindness

16. Sex-linked Disorders Dechenne muscular dystrophy Progressive muscle weakness Missing protein (dystrophin) Hemophilia Absence of protein for blood clotting

17. X-Inactivation Females have two X chromosomes, but one inactivates during embryo development Condenses into Barr body So only one X functions in males AND females Occurs when –CH 3 groups are added to cytosine Gene on inactive X makes this happen A lot more to figure out

18. Chromosome Errors Nondisjunction – homologous chromosomes or sister chromatids do not split evenly into gametes Result – some have more, some have less Abnormal chromosome # - aneuploidy Extra copy – trisomic 1 copy missing – monosomic Extra full sets – polyploidy (occurs in plants)

19. Chromosome Errors Deletion – missing part Duplication – extra piece

20. Chromosome Errors Inversion – reversal Translocation – out of order

21. Resulting Problems Many result in spontaneous abortion Down syndrome Trisomy 21 Specific symptoms Correlation with maternal age Result of nondisjunction during meiosis I

22. Resulting Problems XXY – Kleinfelter’s syndrome XO – Turner syndrome Deletion at #5 – cri du chat Translocations – some cancers Fragile X – abnormally thin section of DNA on X chromosome Symptoms are different if from sperm or egg (worse if from egg)

23. FYI…Cytoplasmic genes Genes found on DNA of mitochondria and chloroplasts (not nucleus) do not follow all the rules