Sex linkage

by hafiz m Waseem university of education Lahore

1. HAFIZ M WASEEM

2. Sex linkage SUBJECT : GENETICS TOPIC: SEX LINKAGE

3. CONTENTS SEX LINKAGE HISTORY TYPES OF SEX LINKAGE SEX LINKAGE IN HUMAN COLOUR BLINDNESS CAUSES OF COLOUR BLINDNESS TYPE OF COLOUR BLINDNESS EXAPLE OD COLOUR BLINDNESS TEST CROSS SYPTOMS DETECTION EFFECTS SEX INFLUENCED TRAIT SEX LIMITED TRAIT CONCLUSION

4. SEX LINKAGE DEFINITION: Sex linkage is the phenotypic expression of an allele that is independent on he gender of the individual and is directly tied to sex chromosome. HISTORY: THOMAS MORGAN: Sex linkage was first discovered by Thomas Morgan in 1910 who observed a disproportionate percentage of white- eye male fruits flies. This experiment involved crossing purebred red-eyed female fruit flies with these mutant white – eyed males. The result was exclusively red – eyed individuals of both sexes.

5. EXAMPLE OF SEX LINKAGE There are some examples of sex linkage. Hemophilia Red- green colour blindness Congenital night blind ness Some high blood pressure genes Fragile X syndrome

6. EXAMPLE OF SEX LINKAGE HEMOPHILIA CONGENITAL NIGHT BLINDNESS

7. Sex linkage in human Twenty genes are sex linked. Red green colour blindness and hemophilia Both these disease are sex linked recessive trait.

8. COLOUR BLINDNESS DEFINITION Colour blindness is a condition in which individuals have difficulty in distinguishing red from green.

9. What animals are colour blind? Cats and Dogs To see in full colour as we know it, humans use three cones red, blue, and green. However cats and dogs have only blue and green cones. This means they have much more muted perception of colour, which akin to colour blindness in humans.

10. Types of colour blindness There are three types of colour blindness. Protanolay: It is a type of o colour blind ness which reduce to red colour. Deuteranomaly Which reduce sensitivity to green color.   Tritanomaly Which reduce sensitivity to blue colour.

11. CAUSES OF COLOUR BLINDNESS E.B Wilson firstly discovered facts about hereditary color blindness It is genetic disease and inherited from mother to child Gene for colour blindness present on X chromosome Colour blindness occurs in about 8% males and only 0.5% in females Some people become colour blind due to other disease like diabetes and medication and multiple sclerosis.

12. TRANSFORMATION OF COLOUR BLINDNESS Why blindness colour is occur more in males instead of females. Father transfer his x chromosomes to all daughter and mother transfer her x chromosome. Son will be colour blind and daughter will be normal if his mother is carrier father is normal Colour blind daughter will be produce only produce only when his father is colour blind and mother is carrier or colour blind. Since such marriages are very rare.

13. TEST CROSS -1 If mother is normal father is colour blind Then son will be normal and daughter will be carrier.

14. TEST CROSS-2 If mother is carrier and father is colour blind. 50 percent chances daughter may be colour blind or carrier. 50 percent chances son will be normal or colour blind.

15. TEST CROSS -3 If mother is colour blind and father is normal. All sons will be colour blind and all daughter will be carriers.

16. SYMPTOMS: Symptoms of colour blindness could range from mild to severe. Example would be difficult distinguishing between colors, or inability to see shades of the same color. Rapid eye movement could occur in rare cases, and sensitivity of bright light. They could also suffer from having trouble seeing the brightness of color in the usual way. Inability to tell the difference between the shades of same or similar colors. Particularly red and green or blue or yellow.

17. DETECTION OF COLOUR BLINDNESS It can be detected by using special charts made up of coloured dots These dots are so arranged that coloured blind person can see a different patterns Sex linked traits in other animals: White eyes in drosophila melanogaster flies – the first sex linked gene discovered. Fur colour in domestic cats : the gene that causes orange pigment is on the X chromosome; thus a calico or tortoiseshell cat, with both black and orange pigment , is nearly always female. The first sex- linked gene ever discovered was the lacticolor X linked recessive gene in the moth.

18. CONTINUE … Sex – influenced traits : Sex influenced or sex conditioned traits are phenotypes affected by whether they appear in a male or female body. Even in a homozygous dominant or recessive female the condition may not be expressed fully. Example : The baldness in humans. Sex limited traits: These are characters only expressed in one sex . They may be caused by gene on either autosomal or sex chromosome

19. EXAMPLE OF SEX INFLUENCED TRAITS BALDNESS IN HUMANS POLYMORPHISM IN HONEY BEES

20. TREATMENT OF COLOUR BLINDNESS There are no treatments for most types of color vision difficulties , unless the colour vision problem is related to the use of certain medicine or eye condition. Discontinuing the medication causing your vision problem or treating the underlying eye disease may result in better color vision .

21. CONCLUSION Morgan’s conclusion was the trait for eye color must be encoded on the X chromosome, and that white eyes must represent the recessive allele.

22. REFRENCES… References: Morgan, Thomas 1919. The physical basis of hereditary Genetics home reference (2006), genetic condition illustration, national library of medicine Don caster L.& Raynor G.H 1906. Breeding experiments with Lepidoptera. Proceeding of the zoological society of London. Ford E.B (1965) Genetics polymorphism . p17 – 25.MIT Press1965. Mallet J. Joron M. (1999) the evolution diversity in warning color and mimicry polymorphisms, shifting balance, and speciation.\ Zirkle, Conway (1946). The discovery of sex influenced , sex limited and sex linked hereditary . Joron M, Papa R, Beltran M, et al (2006). A conserved supergene locus controls colour patterns diversity in Heliconius Butterfly. www.sciencehub .com www.ilamkidunya.com