Dr. Ebraheim’s educational animated video explains X-linked recessive inheritance and provides you with examples and simple pedigree to help comprehend all you need to know about this inheritance type.
The mother is a carrier and it affects the males only.
50% of the males will be affected by the carrier mother.
Think of hemophilia, the mother is carrying the gene, the boys will be affected but the mother is not affected. 50% of the boys will be affected.
In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. XX is a female and XY is a male. The sex-linked traits are usually on the X chromosome because it is larger and has more genes than the Y chromosomes.
If both male and female carry the gene. The female will not be affected because she has a dominant normal gene. The male will be affected because he lacks a dominant normal gene.
When there is no dominant present, the recessive gene will show up and cause the problem.
X-linked recessive inheritance usually occurs in males. Males have one X chromosome and one Y chromosome. If the male has a single recessive gene on the X chromosome, then the disease will occur.
Condition transmitted by X-linked recessive:
1-Haemophilia A: genetic deficiency in clotting factor VIII, which causes increased bleeding and usually affects males. One out of five thousand males is affected.
2-Colored blindness: deficiency in the way you see color. Usually involves inability to distinguish between shades of red and green.
3- Hunter’s syndrome: one of the mucopolysaccharidosis, the defect in the enzyme will affect the body’s ability to break down the glycosaminoglycans.
4- Duchene muscular dystrophy (DMD): it is a nerve demyelination, dystrophin gene is involved, gower sign where hip extensors are usually affected first. It usually affects males.
In Duchene muscular dystrophy, the dystrophin gene is absent, however in Becker muscular dystrophy, the dystrophin gene is decreased or reduced.
5-Spondyloepiphyseal dysplasia tarda (SEDT): type II collagen is involved. It is a random mutation in 50% of the cases. The condition is less severe and does not have lower extremity angular deformity.
What is the difference between autosomal recessive and X-linked recessive inheritance?
Autosomal recessive usually appears in both sexes with equal frequency. It tends to skip generations. The affected offspring are usually born to unaffected parents.
Note: if it is dominant it will not skip a generation.
The X-linked recessive the son will be affected if the mother is a carrier.
Become a friend on facebook:
/ drebraheim
Follow me on twitter:
#!/DrEbraheim_UTMC
Donate to the University of Toledo Foundation Department of Orthopaedic Surgery Endowed Chair Fund:
www.utfoundation.org/foundati...
30 мар 2016
