genetics: explain why a carrier of a certain disease can be phenotypically normal?

Please explain clearly

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  • 9 years ago
    Favorite Answer

    you need to understand the difference between phenotype and genotype this is where your answer lies.

  • Caitie
    Lv 7
    9 years ago

    The last answer here is the best. It indeed is because a lot of genetic diseases are recessive, so parents can be carriers without having the disease.

    The Punnett square in that answer is correct. If you change the concept of eye color to a genetic disease carried on one allele, it is exactly as stated.

    Cystic fibrosis is a genetic disease which is fatal eventually. Set up the same Punnett square as in the answer given, but perhaps use N=normal and n=cystic fibrosis, which is a recessive trait.

    Two parents can unknowingly carry the disease without ever having it themselves, and have a 25% chance every time they have a child of giving this child a recessive gene from each of them.

    Said another way, most genetic diseases are recessive, and if they are autosomal traits (not sex-linked, which is a bit different), a person can be perfectly normal (which means he/she has a dominant allele) yet can still carry the disease without showing any symptoms, and can pass on this recessive gene to the offspring.

    Source(s): retired AP bio and physiology teacher
  • 9 years ago

    A phenotype is charicteriscs that are physically seen (brown hair, blue eyes, freckles)

    Genotype- the actual genes received from both parents. You receive 2 versions of each gene (1 from each parent) For the majority of genes there is a recessive and dominant trait. If you have a dominant gene if you will have that phenotype. That means you could have a recessive gene but it will not be visible because you also have the dominant ( however, you can still pass the recessive on to offsprings.

    To show a recessive trait both parents must give you recessives genes

    So 2 people reproduce

    Person A has blue eyes, which is recessive ( this means this person has ONLY recessive traits (bb))

    Persone B has brown eyes which is dominant This person could have only dominant genes or both (BBor Bb) We will say they are heterozygous and have both (Bb)

    b b

    B Bb Bb

    b Bb bb

    So to answer your question if a person is heterozygous (has both traits) and the given disease is recessive they person will be phenotypically normal because the dominant trait will show

    Source(s): Biology Major
  • Max
    Lv 7
    9 years ago

    Its in the reading. Didnt you do the reading?

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