Question

Hemophilia is Xlinked recessive trait .Consider a cross between a women who is carrier and man who suffers from hemophilia,Which of the folling statements ia true

Answer 1

Answer:

II and III

Explanation:

I. All sons of these parents will be a hemophiliac.

II. A son who suffers from hemophilia received the hemophilia allele from his mother.

III. Half of the daughters of this cross are predicted to be hemophiliacs.

Assuming the haemophilia allele is represented by h, the alternate form being H.

A woman that is a carrier will have the genotype $X^H X^h$.

A man who suffers from haemophilia will have the genotype $X^h Y$

Crossing both of them:

$X^H X^h$   x   $X^h Y$  =  $X^H X^h, X^H Y, X^hX^h and X^hY$

From the result of the cross, the following can be deduced:

• Half or 50% of the sons from the couple will be haemophiliacs.
• Any son that suffers from haemophilia received the allele from the mother.
• Half or 50% of the daughters from this cross will be hemophiliacs.

Hence, statements II and III are true.

Answer 2

I. All sons of these parents will be a hemophiliac.

II. A son who suffers from hemophilia received the hemophilia allele from his mother.

III. Half of the daughters of this cross are predicted to be hemophiliacs

Answer:

II and III are correct

Explanation:

II. A son who suffers from hemophilia received the hemophilia allele from his mother.  

The male sex chromosomes is XY. Since the Y -chromosome  of the father does not bear the haemophilia allele,its inheritance to determine the sex of the child  is not associated  with the haemophilia. Y-chromosomes does not bear any allele.Only one of the X-chromosomes of the  carrier mother should possess the haemophiliac  gene. Therefore a son who is haemophiliac definitely inherited heamophilic - X-chromosomes from the mother(r(,assuming  he picked the defective X-allele of the carrier mother ) and heamophilic  Y-chromosomes fro.m the father. XcY.

III. Half of the daughters of this cross are predicted to be hemophiliacs.

No doubt the daughter chromosomes are XX. The father is haemophiliac, thus his X-Chromosomes carries the allele for heamophlia  The mother carrier  XX chromosomes shows that at least one of the X-chromosomes has  haemophiliac gene. Therefore the probability is that half  of the daughters will be haemophiliac  assuming  one of this daughters inherited the  defective allele on one of  the X-chromosomes   of the carrier mother, the haemophiliac X-chromosomes from the father.

The other daughter may be a carrier assuming,  she inherited haemophiliac  X- gene from the father, and the heamophilia free X-chromosomes from the carrier mother. XcX

let  C- rep. heamophila.

let the haemophiliac father be-XcY

let the haemophiliac mother be XcX

based on mono-hybrid  cross.

                     XcY    x  XcX  

                XcXc     XcY    XXc    XY

→haemophiliac  girl XcXc

→ haemophiliac boy XcY

→carrier girl    XXc

→Normal boy   -XY.

Evidently from the cross I  is WRONG