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    Mutations in DNA/RNA, Cystic Fibrosis, and Meiosis

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    Transcription: During the process of transcription, the information in the DNA codons of a gene is transcribed into RNA.

    Suppose that gene X has the DNA base sequence 3'-TACCCTTTAGTAGCCACT-5'.

    Question: What would be the base sequence of RNA after transcription occurs?

    Translation: During protein synthesis at the ribosome, the base sequence of the mRNA codons is translated to the amino acid sequence of a protein.

    Question: Using the mRNA that you transcribed above, use the genetic code table to determine the resulting amino acid sequence? Turn this in.

    What is the significance of the first and last codons? What meaning do these codons have for protein synthesis?

    C) Mutations: A mutation is defined as a change in the base sequence of DNA. This may occur as a "mistake" in DNA replication, for example.

    Suppose that during DNA replication, two mutant DNA sequences are produced as shown below.

    For the 2 mutated DNA sequences, you will investigate how these changes might affect the sequence of amino acids in a protein.

    Question: For each of the two, you will need to first transcribe the mRNA, and then use the genetic code table to determine the amino acid sequence.

    Question: Then, explain why a change in amino acid sequence might affect protein function. Turn in your answer.

    Here is the original sequence, followed by two mutated sequences, 1 and 2:

    Original sequence 3'- TACCCTTTAGTAGCCACT-5'

    Mutated sequence 1) 3'-TACGCTTTAGTAGCCATT-5'

    Mutated sequence 2) 3'-TAACCTTTACTAGGCACT-5'.

    Punnett Square on Cystic Fibrosis

    A couple who are both carriers of the gene for cystic fibrosis. What is the probability that they will have a child without cystic fibrosis (not a carrier), a child who is a carrier for cystic fibrosis, and a child with cystic fibrosis?

    Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for growth and repair; meiosis produces sex cells (gametes) called sperm and eggs.

    Although mutations are the ultimate source of genetic variability, both meiosis and sexual reproduction also can contribute to new genetic combinations in offspring.

    Question: How do both meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents? Be sure to talk about steps in meiosis that increase variability as well as the process of fertilization.

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    Solution Preview

    In protein synthesis, remember, that A=U; T=A; C=G; and G=C. A= Adenine; U= Uracil; T= Thymine; C= Cytosine; and G= Guanine. So for your first problem you have TACCCTTTAGTAGCCACT= AUGGGAAAUCAUCGGUGA. Each of the three sets of codons represents an amino acid. The amino acid sequence is used to create a protein and the first and last sets are the start and stop codes for protein synthesis.
    Original translation:
    AUG=Methionine or Start
    GGA= Glycine
    AAU= Asparagine
    CAU= Histidine
    CGG= Arginine
    UGA= Stop
    RNA amino acid sequence= Met-Gly-Asp-His-Arg-Stop; You can just take the first three letters of the amino acid name to create the amino acid sequence.
    AUG= Methionine or Start
    CGA= Arginine
    AAU= Asparagine
    CGG= Arginine
    UAA= Stop
    Mutation 2: TAACCTTTACTAGGCACT= ...

    Solution Summary

    This solution includes sequences and how to determine the sequences after transcription occurs. It discusses complications that can occur when mutations occur in DNA. It goes over setting up a Punnett Square for a couple who are carriers for cystic fibrosis and how to determine the probability that their children will be normal, carriers, or have cystic fibrosis. It also discusses mutations that can occur in meiosis.

    There are links included to further help your understanding.