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In humans, Muscular Dystrophy is an X-linked recessive disorder. Inheritance of the BRCA1 gene that can cause breast cancer in women and is an autosomal dominant disorder. A woman, who has tested positive for one copy of the BRAC1 allele, does not have muscular dystrophy. There is no history of muscular dystrophy in her family, but her mother died of breast cancer. The woman is married to a man who has muscular dystrophy. There is no history of BRAC1 beast cancer in his family. What are the probable genotypic and phenotypic ratios of their male children?

Respuesta :

luisvaschetto

Answer:

Muscular Dystrophy : 50%

Breast cancer: 50%

Explanation:

Muscular Dystrophy (linked to X):

1/2 (mother) x 2/2 (father) = 2/4 (50%) chance of having an affected child with MD

Breast cancer (autosomal dominant disorder):

1/2 (mother) + 0 (father) = 1/2 = 50% chance of having an affected child with breast cancer

marianaegarciaperedo

Male children only inherited the X chromosome with the dominant allele. 50% inherited the recessive gene b, and 50% the dominant allele B. Their ratio is 1:1. 50% Normal carrying the breast cancer allele BbX⁺Y: 50% normal bbX⁺Y.  

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Available data:

Muscular Dystrophy is an X-linked recessive disorder.

  •     X⁺ dominant allele for normal trait
  •     X⁻ recessive allele for dystorphy

Breast cancer is caused by an autosomal gene

  •     B allele is dominant and codes for cancer
  •     b allele is recessive and does not cause cancer

Woman:  Bb X⁺X⁺

Man: bb X⁻Y

Cross: woman  x  man

Parentals) Bb X⁺X⁺    x     bb X⁻Y

Gametes) BX⁺,  BX⁺, bX⁺,  bX⁺

                bX⁻,  bY,  bX⁻,  bY

Punnett square)     BX⁺           BX⁺        bX⁺          bX⁺

                  bX⁻    BbX⁺X⁻    BbX⁺X⁻   bbX⁺X⁻    bbX⁺X⁻

                  bY      BbX⁺Y      BbX⁺Y     bbX⁺Y     bbX⁺Y

                  bX⁻    BbX⁺X⁻    BbX⁺X⁻   bbX⁺X⁻    bbX⁺X⁻

                  bY      BbX⁺Y      BbX⁺Y     bbX⁺Y     bbX⁺Y

F1) Females

  • 4/8 = 1/2 = 50% of the females are expected to express breast cancer and to have normal muscles  ⇒  BbX⁺X⁻

  • 4/8 = 1/2 =50% of the females are expected not to express breast cancer and to have normal muscles ⇒ bbX⁺X⁻

    Males

  • 4/8 = 1/2 = 50% of males are expected to carry breast cancer gene and to have normal muscles  ⇒  BbX⁺Y

  • 4/8 = 1/2 =50% of the males are expected not to carry breast cancer gene and to have normal muscles ⇒ bbX⁺Y

The genotypic and phenotypic ratio of male children is 1:1

50% Normal male carrying the breast cance allele: 50% normal male

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