1. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk X-Linked Recessive Inheritance This PowerPoint file contains a number of slides that may be useful for teaching of genetics concepts. You may use these slides and their contents for non-commercial educational purposes. This presentation includes: Pedigrees showing inheritance pattern and features of X-linked recessive inheritance Examples of X-linked recessive conditions.

2. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk X-linked Recessive Inheritance One copy of an altered gene on the X chromosome causes the disease in a male. = Hemizygote Male An altered copy on one of the X chromosome pair causes carrier status in a female. = Heterozygote XX XY Female

3. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk X-Linked Recessive Inheritance l All men who inherit the mutation are affected l Carrier females are usually unaffected l Appears to skip individuals. Carrier female Affected male Normal male

4. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk X-linked Recessive Inheritance Pattern: Males are affected in more than one generation, no affected females. Affected males are linked through unaffected females. Males do not transmit to males. X-linked: The altered gene is on the X chromosome. Males have only one X chromosome and if this is altered, will be affected. Females have two X chromosomes - one normal copy is usually sufficient for adequate cell function. Examples: include haemophilia and Duchenne muscular dystrophy.

5. © 2009 NHS National Genetics Education and Development CentreGenetics and Genomics for Healthcare www.geneticseducation.nhs.uk Examples of X-Linked Recessive Conditions Fragile X syndrome Haemophilia Duchenne muscular dystrophy (DMD) Becker muscular dystrophy (BMD) Fabry disease Retinitis pigmentosa Alport syndrome Hunter syndrome Ocular albinismOcular albinism Adrenoleucodystrophy.Adrenoleucodystrophy.