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Hemophilia is an X-linked recessive genetic disorder. A baby girl is found to have inherited the trait from her parents. What are the phenotypes of the parents?

Sagot :

marianaegarciaperedo

X-linked genes are inherited. The affected girl's father is hemophilic (X-Y), and the mother might be either hemophilic (X-X-) or carrier normal (X+X-).

What are the X-linked genes?

These are the genes located in the X séx chromosome and not in the somatic ones.

Traits coded by these genes are inherited. This is, X-linked genes are transmitted from parents to children through generations.

According to this, X-linked genetic disorder will be inherited as well.

  • Men have a high probability of being affected since they only have one copy of the X chromosome.  
  • In women, the effect of the mutation might be musk in heter0zyg0us state.

Hemophilia is a X-linked recessive genetic disorder.

Let us represent the recessive allele with the symbol -, and the dominant allele with the symbol +.

  • X- is the chromosome carrying the recessive allele
  • X+ is the chromosome carrying the dominant allele

For the affection to be expressed, the person must be either,

  • X-X-  ⇒   woman/girl
  • X-Y  ⇒    man/boy

If the baby girl is found to have inherited the trait from her parents, then her genotype is X-X-. She must have received one X- chromosomes from each parent.

  • Her father provided the X chromosome, so he must be hemophilic (X-Y)
  • Her mother provided the other X chromosome, but she can be either a carrier (heter0zyg0us, X+X-) or hemophilic (h0m0zyg0us recessive, X-X-).

Options,

Cross 1) affected father x carrier mother

Parentals)   X-Y    x    X+X-

Gametes)  X-      Y    X+     X-

Punnett square)       X-       Y

                       X+   X+X-    X+Y

                       X-    X-X-     X-Y  

F1) 1/2 = 50% of the progeny is expected to be healthy (25% X+X- girls + 25% X+Y boys)

    1/2 = 50% of the progeny is expected to be hemophilic (25% X-X- girls + 25% X-Y boys)

Cross 2) affected father x affected mother

Parentals)   X-Y    x    X-X-

Gametes)  X-      Y    X-     X-

Punnett square)       X-       Y

                       X-    X-X-    X-Y

                       X-    X-X-     X-Y  

F1) 100% of the progeny is expected to be hemophilic (50% X-X- girls + 50% X-Y boys)

  • the phenotype of the father ⇒ hemophilic (X-Y)
  • the phenotype of the mother ⇒ normal carrier (X+X-) or hemophilic (X-X-)

You can learn more about séx-linked genes at

https://brainly.com/question/14680914

https://brainly.com/question/15608757

https://brainly.com/question/786413

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