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Pedigree Analysis of Cystic Fibrosis Inheritance

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            Pedigree analysis can be done in order to determine the probability of an offspring inheriting a specific gene, like that of cystic fibrosis.  In the given activity, since a friend’s cousin has cystic fibrosis, then it can be deduced that their grand parent can only be a heterozygous (Cc) or carrier of the gene. Because of this, it can be said that either one of her parent carries the allele for cystic fibrosis, since none of her siblings have the disease (she and her siblings are either homozygous dominant or heterozygous). When the genes independently assort, there can only be three combination formed; it can either be CC, Cc or cc. Thus, the chance of a friend being a carrier becomes 1/3 or 33.33%.   However, it is not ascertained whether she is a homozygous dominant (CC) or heterozygous (Cc). Then the probability of her being either one of those condition becomes 2/3 or 66.66%.  In the case of her fiancé, who has a sister that have cystic fibrosis, it can be said that he can be either a normal person (homozygous dominant) or a carrier (heterozygous), since both of his parent can only be a carrier of the disease.  And the chance of him being either a carrier or a not is also 2/3 or 66.66%.

In Mendel’s Law of Independent Assortment, segregation of genes can be determined using general rules of probability.  Chance of two independent events can be determined by multiplying the probability (Campbell, 2000, p.246). Thus, the probability of each spouse (2/3) multiplied by the probability of the gene expression (1/4), will yield a 1/9 probability or 11.11%.

Given the probability of passing on the traits to the offspring (1/9 or 11.11%), it would still be better to be extra cautious and seek advice from medical expert when starting up a family.  Extensive researches are being done to combat those lethal genes known, like that of Huntington’s disease. Organizations such as Scottish Huntington’s Association has been supporting in making the breakthrough in finding the cure for such disease (Lamont, 2008).


Campbell, N., Reece, J., & Lawrence, M. (2000). Biology 5th ed. Singapore: Pearson Education

Asia Pte Ltd.

Scottish Huntington’s Association. (2008). Why Effective Therapies are Possible by Don

Lamont. Retrieved March 7, 2008, from http://www.hdscotland.org/Research %20Updates.htm

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