Question

1. Examine each pedigree shown (a-c). The shaded square/circle shows an inherited phenotype. For each (a, b, c), write a sentence or two that indicates whether it is (or is not) consistent with X-linked recessive inheritance. If you decide the pedigree IS consistent, for full credit you must prove this by setting up a Punnett square or a forked line diagram. (6 pts) TO GO 2. Vitamin D-resistant rickets is a genetic condition inherited as X-linked dominant. A husband has this Vitamin D-resistant rickets but his wife does not. What is the probability that their first child will be a: (4 pts) a) normal son? b) normal daughter? c) son with Vitamin D-resistant rickets? d) daughter with Vitamin D-resistant rickets

Answer 1

Answer-

1) a) This pedigree supports X linked recessive inheritance.

b) this supports X linked recessive inheritance.

c) this does not support X linked recessive inheritance.

2) Probability of having first child as son will be 50%. Probabilty of having first child as daughter will also be 50%

a) probability of having normal son is 50% as he gets only normal allele from his mother.

b) probability of having normal daughter will be 0% as she will get one dominant allele from affected father.

c) probability of having affected son will be 0% as he gets Y chromosome from affected father.

d) probability of having affected daughter will be 50% as she gets dominant allele from father.

Explanation for all answers is given below:

In x linked recessive inheritance Affected mate should have genotype all 1 female " " alla all Alla 1 alla 0 o = 1 e Alla Alf Affected father (I-1) has one affected daughter (II - +) and one unaffected daughter (II-2) I-2 gets normal gene from mother. This is consistent with X linked rocosive inheritance Punett square k (1-1) Alla I-2 I-3 I-2 V alla all II - 1 (b) All Alla I-1 punnett - square H all AL A Alr I-3 AIN in Affected son (II-2) has I-2 unaffected parents. He gets only recessive x Alla all chromosome from carier. I-2 I-1 mother. others are normal This is consistent with x lunked recessive enheritance

All alla H I 2 3 4 so o I ( Alla all "Alla It should be all and affected as it receives a from mother Affected mother (I-2) has unaffected son (I-1) This does not fit x linked recessive trait) Punnett square cI-1 als Alla I-2 II-2 To support x linked recessive trait I-1 should have genotype all and affected. I-2 Alla I-4 dominant. vitamin D-resistant ricket x linked Affected father -> genotype oli Normal mother - genotype alld Drzo dild Yolld (Affected daughter) (d) Daughter will be affected die. with vitamin D resistant ricket. oli 20 alld dir ay son will be normal.