Question

Sex Linked Traits 4. Assume you are a genetic counselor and a couple comes to you for counseling They want to know if there is any chance that their first baby might have muscular dystrophy. M.D. is a sex linked recessive trait. Neither of the parents has M.D. but the wife's father has M.D. Prove your answer by showing the genotypes and phenotypes of the parents, grandparents and possible offspring. Parents Fill in the boxes Genotype Phenotype Possible Genotypes or Carrier phenotypes Disease Mother Father Grandmother Grandfather Normal Punnett Square show your cross (Grandparents) Punnett Square show your cross (Parents) Explanation: Would any of the girls born have M.D.? Would any of the boys bom to this couple have a chance of having M.D.? Explain your answer using your data.

Answer 1

Answer: 4

	Genotype	Phenotype
Possible Genotypes or Phenotypes	XM XM XM Y	Normal female Normal male
	XM Xm	Carrier female
	Xm Xm Xm Y	Diseased female Diseased male
Mother	XM Xm	Carrier
Father	XM Y	Normal
Grandmother	XM XM	Normal
Grandfather	Xm Y	Diseased

1) Cross of Grandparents:

XM XM        *        Xm Y

Punnet square

	XM	XM
Xm	XM Xm Carrier female	XM Xm Carrier female
Y	XM Y Normal male	XM Y Normal male

2) Cross of parents:

XM Xm     *    XM Y

Punnet square:

	XM	Xm
XM	XM XM Normal female	XM Xm Carrier female
Y	XM Y Normal male	Xm Y Diseased male

Explaination:

The above cross between parents show that girl child born will be Normal (XM XM). One of them will be Carrier (XM Xm). But she is phenotypically normal

One of the Boy child will be normal (XM Y) ; while other will be diseased (Xm Y)

This is sex linked recessive trait. It expresses in its homozygous recessive state in female, while in male one of recessive allele will lead to disease.

Recessive allele (Xm ) is inherited from grandfather to his daughter (present mother). But as grandmother was normal, so their daughter (present mother) is carrier but phenotypically normal.

Male parent is normal and female parent is carrier (phenotypically both normal), girl will be normal / carrier while boy will be normal / diseased.

Answer: 5.

	Genotype	Phenotype
Possible genotype or phenotypes
Mother	IOIO	Blood group O
Man if the father	IAIO	Blood group A
Man if not the father	IAIA	Blood group A

Since: IA is dominant over IO

1) If the man is the father

	IO	IO
IA	IAIO Blood group A	IAIO Blood group A
IO	IOIO Blood group O	IOIO Blood group O

1) If the man is not the father

	IO	IO
IA	IAIO Blood group A	IAIO Blood group A
IA	IAIO Blood group A	IAIO Blood group A

Explaination:

If child is having blood group O then, its both parents must have at least one IO allele.

Since mother is having blood group O, she is homozygous for blood group O (IO IO )

So the father must be heterozygous for blood group A (IA IO).

Since IA is dominant over IO

If man is not father of child he will be homozygous for blood group A (IA IA).