Sex linked inheritance

A basic information about sex linkage and its diseases.

1. CharthaGaglani

2. CONTENTS
•What is sex linked inheritance?
•Types
1.X-linked inheritance ( Colour Blindness and
Haemophilia )
2.Y-linked inheritance ( Hyperterichosis, Ichthyosis
hysterix )
3.Completely sex linked inheritance
4.Incompletely sex linked inheritance

3. SEX-LINKED INHERITANCE
•Theinheritanceofatrait(phenotype)thatis
determinedbyagenelocatedononeofthesex
chromosomesiscalledsexlinkedinheritance.
•Thegenescontrolledbygeneslocatedonthesex
chromosomeiscalledsex-linkedinheritance.
•ItwasdiscoveredbyT.H.Morganin1910.

4. •ThegenescontrollingbodycharacterslocatedonX
chromosomesarecalledX-linkedgenes.
•TheinheritanceofX-linkedgenesiscalledX-linked
inheritance.
•ThecharacterscontrolledbyX-linkedgenesare
calledX-linkedcharacters.
•Eg:Haemophilia,colorblindnessetc.

5. •ThegenescontrollingbodycharacterslocatedonY
chromosomearecalledY-linkedgenes.
•TheinheritanceY-linkedgenesiscalledY-linked
inheritance.
•ThecharacterscontrolledbyY-linkedgenesiscalled
Y-linkedcharacters.
•Eg:Hyperterichosis,Ichthyosishysterix.

6. •ThegenescontrollingbodycharactersofbothandX
andYchromosomeiscalledXYlinkedgenes.
•TheinheritanceofXYlinkedgenesiscalledXY
linkedinheritance.
•ThecharacterscontrollingtheXYlinkedgenesare
calledXYlinkedcharacters.
•Eg:Nephritis,Xerodermapigmentosumetc.

7. •Most of the sex linked genes follow the criss-
cross inheritance (zig zag).
•The inheritance of a character from the father
to his grandson through his daughter is called
criss-cross inheritance.

8. X-LINKED INHERITANCE
•CertainsexlinkedgenesarelocatedonlyonX
chromosomesandtheirallelesareabsentfromY
chromosome.
•ThesegenesarecalledXlinkedgenes,thecharacters
controlledbythesegenesarecalledXlinked
charactersandtheirmodeofinheritanceiscalledX
linkedinheritance.
•Eg:Colourblindness,Haemophiliaetc.

9. COLOUR BLINDNESS
•Colourblindnessisasexlinkedcharacter
discoveredbyWilsonin1911.
•Hereditarydiseaseandtheaffectedpersoncannot
distinguishbetweenredandgreencolour.
•Redblindnessiscalledprotonopiaandgreen
blindnessiscalleddeutronopia.
•Colourblindnessisarecessivecharacter.

10. •Causedbyrecessivegenesrepresentedbycc.
•NormalpersoncontaingenesCCorCcorCalone(
inman).
•ThegenesforcolourblindnessarelocatedontheX
chromosome,theirallelesarenotpresentonY
chromosome.
•Somanhasonlyonegene.Thepresenceofonlyone
geneforacharacteriscalledhemizygous.Somanis
hemizygoteforcolourblindness.

11. •Thischaracteriscommoninmantheninwoman.
•Followscriss-crossinheritance.
•Nevertransmittedtosonfromfather.
•Daughtercarryingonerecessivegeneforcolour
blindnessiscalledcarrier.

13. HAEMOPHILIA
•AlsocalledasBleeder`sdisease.
•Characterizedbydelayedbloodclotting.
•Thisisbecauseoftheabsenceofantihaemophilic
globubinwhichplaysanimportantroleinblood
clotting.
•Innormalperson,bloodclotsin2to8minutesbutin
haemophilicpatients,clottingisdelayedfor20
minutesto24hours.Hencetheybleedcontinuously
fromthewound.

14. •QueenVictoriawasalsoaffectedbythisdiseaseand
itwastransmittedtoherdescendants.
•HencethisdiseaseiscommonamongtheRoyal
FamilyOfQueenVictoriaandsoitisalsocalledas
Royaldisease.
•Itisasexlinkedrecessivecharacter.
•Causebyrecessivegenerepresentedashhand
normalconditionisduetodominantgeneH.

15. •ThegenesarelocatedonXchromosome.
•Maleishomozygote.
•Diseaseiscommoninmaletheninfemale.
•Followscriss-crossinheritance.
•GenerallyHaemophilicpatientswilldiebefore
reachingreproductivestage.

17. Y-LINKED INHERITANCE
•ThesexlinkedgeneslocatedonYchromosomesarecalled
Ylinkedgenes.
•TheYlinkedgenesareconfinedtomalesonly.
•HencetheyarecalledHolandricgenes(Holos-whole;
andros-male).
•Thesegenesaretransmitteddirectlyfromfathertotheson.
•TheirmodeofinheritanceiscalledYlinkedinheritance.
•Eg:Hyperterichosis,Ichthyosishysterixetc.

19. XY LINKED INHERITANCE
•CertainsexlinkedgenesarelocatedonbothXandY
chromosomes.
•TheyarecalledXYlinkedgenesandtheirmodeof
inheritanceiscalledXYlinkedinheritance.
•Eg:Xerodermapigmentosum,nephritis,retinitis
pigmentosaetc.

20. COMPLETELY SEX -LINKED INHERITANCE
•TheXandYchromosomesarenotsimilar.
•XchromosomeislargerthenYchromosome.
•Thelowerpartofboththechromosomesaresimilar.
Thesetwopartsarecalledhomologousregions.They
havesametypeofgenes.
•Theremainingpartisnotsimilar.Theyarecalled
non-homologousregions.Donotcontainsimilartype
ofgenes.

21. •The genes located on non-homologous regions inherit
together because crossing over does not occur in
these regions.
•The genes located on non-homologous regions are
called completely sex linked genes and their
inheritance is called completely sex linked
inheritance.
•Eg: Haemophilia, colour blindness etc.

22. INCOMPLETELY SEX LINKED INHERITANCE
•Thegeneslocatedonhomologousregionsofsex
chromosomesdonotinherittogetherbecause
crossingovermayoccurintheseregions.
•Sothesegenesarecalledincompletelysexlinked
genesandtheirmodeofinheritanceiscalled
incompletelysexlinkedinheritance.
•Eg:Retinitispigmentosa,nephritisetc.

23. THANK YOU…