Question

Shown below is a pedigree of an individual X who is suffering from ocular albinism which results in permanent vision loss. Use the pedigree to answer the questions that follow:

(a) Complete the following statement about this disease: The trait for the disease is linked to ___________ (X-chromosome/Ychromosome/autosome) and is __________ (dominant/recessive). 

(b) Give a reason to support your answer to (a). 

(c) Identify the genotypes of individuals P, Q, R and S marked in the pedigree. 

Answer 1

(a) The trait for the disease is linked to X-chromosome and is recessive. 

(b) It is appearing in both males and females but more in males which need only one X chromosome for the trait to be expressed.

The trait is being expressed in only in some children/small fraction and so is likely to be recessive.

(c) P: XY 

Q: X_oX

R: X_oX 

S: XY