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Posted by on Tuesday, June 30, 2009 at 9:25pm.

A child is born witrh cystic fibrosis-a recessive trait. However, both his parents do not exhibit the trait. How is this possible?

  • biology - , Tuesday, June 30, 2009 at 9:30pm

    I suspect his parents are both carriers, carrying the recessive gene, but because neither is homozygous, neither have the disease.

  • biology - , Wednesday, July 1, 2009 at 11:49am

    In case you are not familiar with bobpursley's terms, here is a more detailed explanation.

    With recessive traits, a person must have both genes for the recessive condition (homozygous) to show the physical trait. If one of the gene pair are dominant, it will prevent the recessive gene from being expressed in the physical traits (phenotype). That person will be a carrier for that trait, having the genes in the genotype but not showing the trait in the phenotype. However, there is a 25% chance that both carrier parents will contribute the recessive gene to an offspring, making the offspring homozygous for that trait. This means that the child will show the trait in the phenotype.

    This is true for any recessive trait.

    I hope this helps a little more. Thanks for asking.

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