Question

Look at the following pedigree for a sex-linked trait to answer the questions below. a) Is the allele for this trait found on the X or the Y chromosome? __________ b) Is this a dominant or a recessive trait? ___________ c) Give the genotype of all the individuals d) If individual A has children with an unaffected male, what are the chances that her children will have the trait? e) Individual B marries an unaffected woman. What are the chances that they will have affected children?
#7a, b, c, d

Answer 1

Please find the answers below:

Part a) It can be clearly seen from the pedigree that the affected father passes on the diseased allele to some of the male offsprings and all the female offsprings. Since not all the male offsprings are affected, it clearly means that the allele is located on X chromosome of the father.

Part b) It can be clearly seen from the pedigree that the females are affected fromt the disease which means that the disease-allele must be dominant in nature.

Part c) The genotype of affected father will be X^AY, daughter will be X^AX and affected son will be X^AY.

Part d) The genotype of A will be X^AX and that of B will be X^AY. Thus, the Punnett square can be made as below:

	XA	X
XA	XAXA	XAX
Y	XAY	XY

Thus, chances of having an affected offspring will be: 3:1 i.e. 75% of offsprings will be affected.

Part e) If B with genotype X^AY marries an unaffected woman with genotype XX, the Punnett square will be formulated as:

	XA	Y
X	XAX	XY
X	XAX	XY

Thus, the offsprings will be: Affected : Unaffected : : 1:1 i.e. 50% offsprings will be affected.