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SEX LINKAGE

SEX LINKAGE. Characters which are associate more with one gender. © 2007 Paul Billiet ODWS. Characters associated with gender. Anhiorotic ectodermal dysplasia Small teeth, no sweat glands, sparse body hair Occurs primarily in men Never transmitted from father to son

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SEX LINKAGE

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  1. SEX LINKAGE Characters which are associate more with one gender © 2007 Paul Billiet ODWS

  2. Characters associated with gender Anhiorotic ectodermal dysplasia • Small teeth, no sweat glands, sparse body hair • Occurs primarily in men • Never transmitted from father to son • Unaffected daughters may pass the condition onto their sons (the grandsons) © 2007 Paul Billiet ODWS

  3. Sex linkage explained http://nobelprize.org/nobel_prizes/medicine/articles/lewis/index.html • Thomas Hunt Morgan in The Fly Room!(Columbia University 1910) • Fruit Flies (Drosophila melanogaster) © 2007 Paul Billiet ODWS

  4. Character Traits Eye colour Red eye (wild type) White eye (mutant) P PhenotypesWild type (red-eyed) female x White-eyed male F1 Phenotypes All red-eyed Red eye is dominant to white eye The case of the white-eyed mutant © 2007 Paul Billiet ODWS

  5. Hypothesis A cross between the F1 flies should give us: 3 red eye : 1 white eye So far so good © 2007 Paul Billiet ODWS

  6. An interesting observation © 2007 Paul Billiet ODWS

  7. A reciprocal cross Morgan tried the cross the other way round white-eyed female x red-eyed male ResultAll red-eyed females and all white-eyed males This confirmed what Morgan suspected The gene for eye colour is linked to the X chromosome © 2007 Paul Billiet ODWS

  8. A test cross Phenotypes F1 Red-eyed female x White-eyed male Expected result 50% red-eyed offspring: 50% white-eyed offspring Regardless of the sex Observed Results © 2007 Paul Billiet ODWS

  9. Genetic diagram for sex linked genes © 2007 Paul Billiet ODWS

  10. Genetic diagrams for sex linked genes © 2007 Paul Billiet ODWS

  11. © 2007 Paul Billiet ODWS

  12. © 2007 Paul Billiet ODWS

  13. This gene has its LOCUS on the X-chromosome It is said to be SEX-LINKED © 2007 Paul Billiet ODWS

  14. X-linked genes • In sex linked characteristics the reciprocal crosses do not give the same results • For X-linked genes fathers do not pass the mutant allele onto their sons • For X-linked genes fathers pass the mutant allele onto their daughters who are carriers • Carrier mothers may pass the allele onto their sons (50% chance) • Females showing the trait for an X-linked mutant allele can exist but they are rare • Female carriers may show patches of cells with either trait due to X chromosome inactivation © 2007 Paul Billiet ODWS

  15. Tortioseshell Cats are Female © 2007 Paul Billiet ODWS

  16. Daltonism = Red-Green Colourblindness Normal vision Colour blind simulation http://www.onset.unsw.edu.au/issue1/colourblindness/colourblindness_print.htm © 2007 Paul Billiet ODWS

  17. LIGHT Optic nerve fibres Ganglion layer Bipolar cells (neurones) Synapse layer Rod cell Nuclear layer Inner segments packed with mitochondria Cone cell Rod and cone outer segments The retina © 2007 Paul Billiet ODWS

  18. PHOTORECEPTION © 2007 Paul Billiet ODWS

  19. Damaged blood vessels Thrombin Active enzyme Prothrombin Inactive enzyme Fibrinogen Globular protein Fibrin = Clot Fibrous protein Blood Clotting and Haemophilia A simplified scheme of the important steps © 2007 Paul Billiet ODWS

  20. Contact with collagen fibres in blood vessels Factor III Thromboplastin released from blood vessel walls Factor XII (inactive)  Factor XII (active) Factor XI (inactive)  Factor XI (active) Factor IX (inactive)  Factor IX (active) Antihaemophilic factor B Factor VIII Antihaemophilic factor A Factor X (inactive)  Factor X (active) Ca2+ ions and blood platelets Factor II (inactive)  Factor II (active) Prothrombin Thrombin Factor I (inactive)  Factor I (active) Fibrinogen Fibrin Vitamin K precursor © 2007 Paul Billiet ODWS

  21. The antihaemophilic factors • The blood clotting reaction is an enzyme cascade involving Factors XII, XI, IX, X and II • Each of these enzymes are proteases that cut the next protein in line • Other factors including proteins like Factor VIII are essential as coenzymes © 2007 Paul Billiet ODWS

  22. Heamophilia • About 85% of haemophiliacs suffer from classic haemophilia (1 male in 10 000) • They cannot produce factor VIII • The rest show Christmas disease where they cannot make factor IX • The genes for both forms of haemophilia are sex linked • Haemophiliacs do clot their blood slowly because there is an alternative pathway via thromboplastin © 2007 Paul Billiet ODWS

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