sex-linked inheritance. certain traits are carried on the ‘x’ chromosome. certain traits are...

Sex-Linked InheritanceSex-Linked Inheritance

Sex-Linked Inheritance

• Certain traits are carried on the ‘X’ Certain traits are carried on the ‘X’ chromosome.chromosome.

• These traits are recessive.These traits are recessive.• Examples include; baldness, colour-Examples include; baldness, colour-

blindness, and haemophiliablindness, and haemophilia..


• For a For a femalefemale to express the phenotype to express the phenotype she must have the allele on she must have the allele on bothboth her X her X chromosomes.chromosomes.


• For a For a femalefemale to express the phenotype to express the phenotype she must have the allele on she must have the allele on bothboth her X her X chromosomeschromosomes..

Normal Normal X XX X


• For a For a femalefemale to express the phenotype to express the phenotype she must have the allele on she must have the allele on bothboth her X her X chromosomes.chromosomes.

Normal Colorblind Normal Colorblind X X XX X XccXXcc


• For a For a femalefemale to express the phenotype to express the phenotype she must have the allele on she must have the allele on bothboth her X her X chromosomeschromosomes..

Normal Colorblind Carrier Normal Colorblind Carrier

X X XX X XccXXc c X XccXX


• However, a However, a male male will express the will express the phenotype if the allele is on his single X phenotype if the allele is on his single X chromosome.chromosome.

NormalNormal X YX Y


• However, a However, a male male will express the will express the phenotype if the allele is on his single X phenotype if the allele is on his single X chromosomechromosome..

Normal Colourblind Normal Colourblind X Y XX Y XccYY


• However, a However, a male male will express the will express the phenotype if the allele is on his single X phenotype if the allele is on his single X chromosome.chromosome.

Normal Colourblind Carrier Normal Colourblind Carrier X Y XX Y XccY n.s.t.Y n.s.t.


• It is It is muchmuch less likely for females to have sex- less likely for females to have sex-linked diseases than males because they need linked diseases than males because they need to inherit the allele from to inherit the allele from bothboth of their parents of their parents in order to have the disease.in order to have the disease.


• It is It is muchmuch less likely for females to have sex- less likely for females to have sex-linked diseases than males because they need linked diseases than males because they need to inherit the allele from to inherit the allele from bothboth of their parents of their parents in order to have the disease.in order to have the disease.

• Males only need to acquire Males only need to acquire one affected X one affected X chromosome to chromosome to have have the disease because the the disease because the Y chromosome does not have a healthy allele Y chromosome does not have a healthy allele to compensate.to compensate.

The End

sex-linked inheritance. certain traits are carried on the ‘x’ chromosome. certain traits are...

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