Question

Observe the given pedigree chart depicting inheritance of haemophilia.

Blood tests of individuals $P$ and $R$ confirm that they are carriers of haemophilia. What will be the probability of first female child of $P$ and $Q$ to be haemophilic (X) and first male child of $R$ and $S$ to be haemophilic (Y)?

• A. X - $50\%$ Y - $75\%$
• B. X - $75\%$ Y - $25\%$
• C. X - $50\%$ Y - $50\%$
• D. X - $25\%$ Y - $25\%$

Answer 1

The correct option is C X - $50\%$ Y - $50\%$

• Haemophilia is a sex-linked recessive disease.
  
• P and R are carriers of Hemophilia so the genotype will be X${}_c$X.
  
• Q is an infected male who will have a genotype X${}_c$Y.
  
• The first female child of P and Q can be a carrier (XX${}_c$) or infected daughter X${}_c$X${}_c$.
  
• So, the probability of an affected hemophilic child will be 50%.
  
• S is an unaffected male. The genotype is XY.
  
• The first male child of R and S can have genotypes X${}_c$Y or XY.
  
• So, the probability is 50%.
  

So, the correct option is 'X - 50% Y-50%'