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I am tasked with analyzing the transmission of a genetic disease through several...

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dgault11 | (Level 1) Honors

Posted July 19, 2013 at 4:24 PM via web

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I am tasked with analyzing the transmission of a genetic disease through several generations. Males are indicated by square, females by circles. Individuals with the disease are colored solid black. Speculate on the genetic basis by which this disease is inherited. If any known carriers (those carrying the gene, but not manifesting symptoms of the disease) can be identified, list the individuals.

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trophyhunter1 | College Teacher | (Level 3) Senior Educator

Posted July 19, 2013 at 10:16 PM (Answer #1)

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This pedigree chart indicates a disorder that is inherited as a sex-linked trait along the X chromosome. Let X represent the normal allele on the X chromosome and X- represent the sex-linked allele. In the P generation(parental generation), the mother is a carrier and her chromosomes are X X- and the father is normal XY. In the F1 generation, there are four children. We will read it from left to right--a normal male(the unshaded square) who is XY, a male with the disorder(shaded square)who is X-Y, a female who doesn't have the disorder--she is the unshaded circle, and another female who has to be a carrier X-X. She is represented by the last unshaded circle. The first son in the F1 generation(on the left side of the chart) marries a female and has two children, a male with the disorder and a female who doesn't have the disease. In order for the son to inherit the disease, his mother had to be a female carrier-- X-X. He inherited the sex-linked gene from his mother and a Y chromosome from his dad, who was normal. The daughter in the F2 generation on the second row, last unshaded circle, marries an unaffected male. She must be a female carrier X-X.  They have three children, a daughter who is a female carrier, a son with the disorder X-Y and a normal son XY. The only way for the affected male to get the gene is from his mother, who had to be a female carrier. Finally, if observe the F3 generation, the couple in the center, near the bottom of the chart, have one female child who has the disease. The only way for a girl to inherit a sex-linked disease is for both parents to pass down the gene to her. Therefore, her father is an affected male (X-Y) and her mother had to be a female carrier (X-X). Her genotype is X-X-. Some examples of sex-linked traits are red-green colorblindness and hemophilia.

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