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X Linked Inheritance
Transmission patterns

2. © 2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
Fig. 1.10 ©Scion Publishing Ltd
Pedigree of Martin Davies’s family.
Assuming this is X-linked muscular dystrophy, the women marked with dots are obligate carriers of the disease
gene – that is, they must be carriers because they have both parents and offspring who are affected or carriers.

3. © 2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
Fig. 1.16 ©Scion Publishing Ltd
Pedigree of an X-linked dominant condition.
Although heterozygous females are affected, such conditions are usually milder and more variable in females
than in males.

4. © 2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
X-chromosomes shown
Therefore, Anne is not a carrier for
Duchenne muscular dystrophy
Tracking the inheritance of the gene causing Duchenne
muscular dystrophy through the family

5. © 2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
X chromosomes only are shown
This pedigree pattern can be explained by deducing the inheritance of the maternal X
chromosomes

6. © 2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcare
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or
X chromosomes only are shown
An equal chance of being a carrier or not

7. © 2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
or
X chromosomes only are shown
An equal chance of being a carrier or not