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Achondroplasia, a form of dwarfism is inherited as an autosomal dominant. Two dwarfs...

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xkat123 | Student, Undergraduate | (Level 1) Honors

Posted March 15, 2013 at 1:18 AM via web

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Achondroplasia, a form of dwarfism is inherited as an autosomal dominant. Two dwarfs both of whom had one parent of normal height, marry and plan to have a child. What is the probability that their first child will be a dwarf?

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trophyhunter1 | College Teacher | (Level 3) Senior Educator

Posted March 15, 2013 at 2:59 AM (Answer #1)

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Both parents would be heterozygous for Achondroplasia. That means they each have one gene for Achondroplasia and one gene for normal height. Let A stand for Achondroplasia and lower case a stand for normal height gene. Following Mendelian genetics principles, Aa x Aa, the genotypes of the offspring are as follows: 25% AA, 50% Aa and 25% aa. This will produce 75% chance of their offspring having Achondroplasia and 25% chance of them having normal height. It is a 3:1 ratio. Remember that since Achondroplasia is a dominant gene, a person only needs to inherit one copy of that gene to be expressed in the phenotype.

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