Genetics Student Response Original DNA Strand: 3\'-T

Genetics

Student Response

Original DNA Strand:

3'-T ACCCTTTAGCCACT-5'

Transcription (base sequence of RNA):

3'-A UGGGAAAUCGGUGA-5'

Translation (amino acid sequence):

Met -- Gly -- Asn -- His -- Arg -- STOP

Mutated gene sequence one:

3'-T ACGCTTTAGCCATT-5'

Transcription (base sequence of RNA):

3'-A UGCGAAAUCGGUAA-5'

Translation (amino acid sequence):

Met -- Arg -- Asn -- His -- Arg -- STOP

Mutated gene sequence two:

3'-T AACCTTTACTAGGCACT-5'

Transcription (base sequence of RNA):

3'-A UUGGAAAUGAUCCGUGA-5'

Translation (amino acid sequence):

Ile -- Gly -- Asn -- Asp -- Pro-STOP

What is the significance of the first and last codons of an mRNA transcript?

The first codon ("Met") indicates the beginning of the transcription sequence. The last codon indicates the end of a protein sequence, which stops transcription.

Explanation:

Each protein sequence is coded with a starting and ending point, to indicate the length and type of the protein according to the sequence transcribed from the DNA template to the mRNA.

What meaning do these mRNA codons have for protein synthesis?

Each codon consists of three bases, which stand for a particular amino acid. A string of mRNA with groups of amino acids become grouped together and the combination thereof leads to the creation of a protein.

Explanation:

Proteins are synthesized through the translation of mRNA. tRNA recognizes the codons and duly provides the appropriate amino acid (for example, GGA stands for amino acid "Gly." rRNA then creates the protein out of the combination of amino acids.

Did the two mutations result in a change in the final proteins? If so, describe the change.

Both mutations have altered the final proteins. The first mutation changed the protein itself, while the second mutation disabled the protein entirely.

Response / explanation:

One letter change can completely alter an amino acid sequence. The first mutation changed a codon, which altered the second amino acid, thereby changing the protein to be made. Because the second mutation does not have the starting codon (AUG for "Met"), then the tRNA does not start translating the respective sequence.

In general, why might a change in amino acid sequence affect protein function?

The synthesis of proteins is determined by the string of amino acids found in each sequence. By changing a specific amino acid in a protein, there is the chance that the protein itself is altered, perhaps in such a way that it no longer performs the functions that it is labeled to do.

Explanation:

The body relies on proteins to bind, cut, and maintain the activities that keep the body going. A breakdown in a particular protein might spell negative effects. For example, somebody who is lactose intolerant owes it to the fact that there is a mutated DNA sequence that inhibits his body from making the lactase protein.

Part II

Punnett Square

a. Chances (%) for healthy child, not a carrier

b. Chances (%) for child that is carrier for cystic fibrosis trait

c. Chances (%) for child with cystic fibrosis

Sally (Cc), Bob (Cc) both heterozygous

Fill out/adapt Punnett Square:

CC

Cc

Cc

cc

a. Chances (%) for healthy child, not a carrier: 25%

b. % for child that is carrier for cystic fibrosis trait: 50%

c. % for child with cystic fibrosis: 25%

Part III: Essay

How do both meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents?

Include steps in meiosis that increase variability

Include the process of fertilization.

(1) Meiosis has a unique way of dividing its chromosomes onto the offspring. Where mitosis replicates and produces diploid gametes as a finished product, meiosis does not. The process of meiosis results in the production of haploid gametes -- that is, "two consecutive nuclear divisions to halve the number of chromosomes" (Ding, 2010).