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Sunday, January 06, 2008

Widely spaced eyes, increased facial hair and deafness

008. In a family, the father has widely spaced eyes, increased facial hair and deafness. One of the three children has deafness with similar facial features. The mother is normal. Which one of the following is most likely pattern of inheritance in this case ?

1. Autosomal dominant.

2. Autosomal recessive.

3. X-linked dominant.

4. X-linked recessive.

Answer

???

Reference:

Harrison 16th Edition Page 374

Robbins 7th Edition Page 150

Quality

Confusa

Status

Repeat, but with different choices and a trap

QTDF

All books

Discussion

We have few details

  1. The father is affected
  2. Mother is not affected
  3. one among three Children are affected (2 not affected)

Now let us consider the following possibilities

  1. The disease is transmitted in an Autosomal dominant fashion
  2. The disease is transmitted in an Autosomal Recessive forms
  3. The disease is transmitted in a X-linked dominant form
  4. The disease is transmitted in a X-linked recessive form

We proceed to work out the possibility of an affected father and a normal mother in each of the four instances and look what we get

Autosomal Dominant

If the disease is transmitted in an Autosomal Dominant form (A-diseased and a-not diseased) then the Father will be of either AA or Aa (not aa) and the mother aa

If father is AA and mother aa, the offsprings will be

  1. Aa – 100 % - affected

If father is Aa and mother aa, the offsprings will be

  1. Aa – 50 % affected
  2. aa – 50 % not affected

Autosomal recessive

If the disease is transmitted in an Autosomal recessive form (A-not diseased and a-diseased), then the affected father will be of aa and the mother can be AA or Aa (not aa).

If father is aa and mother AA, the offsprings will be

  1. aA – 100 % not affected, (but carriers)

If father is aa and mother Aa, the offsprings will be

  1. aA – 50% not affected, carrier
  2. aa – 50% affected

X-linked Dominant

If the disease is transmitted in a X-linked Dominant form(X-diseased and x-not diseased), then the affected father will be of XY (and not xY) and the mother will be xx (and not XX or Xx).

If father is XY and mother xx, the offsprings will be

  1. Xx – 50 % affected Girl
  2. Yx – 50 % a normal boy

X-linked Recessive

If the disease is transmitted in a X-linked Recessive form (X-not diseased and x-diseased), then the father has to be xY and the mother XX or Xx.

If father is xY and mother XX, the offsprings can be

  1. xX – 50 % - girl - not affected
  2. YX – 50 % - boy -not affected

If father is xY and mother Xx, the offsprings can be

  1. xX – 25 % - girl – not affected
  2. xx– 25 % -girl - affected
  3. YX– 25 % - boy – not affected
  4. Yx– 25 % - boy – not affected

So, in all four conditions, we have a scenario where few children are affected and few children are not affected.

Explanation

Thus we are not able to come to a conclusion with the given data

Comments

If the girl children are affected and the boy children are normal, then we can go for x-Linked Dominant

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