Question

Dr. stevens is examining the dna sequences of a group of mice. he notices that in one of the mice, one nucleotide pair is substituted with another in the part of the dna sequence that codes for fur color. however, despite the substitution, the mouse still has the same fur color as the other mice with the correct dna sequence.why doesn't the substitution of nucleotides in the mouse change its phenotype, or physical characteristics?

Answer 1

The nucleotide substitution might not alter the mouse's fur color due to a silent mutation, the complete dominance of the wild-type allele, genetic robustness, or epistasis where other genes can compensate for the mutation.

Step-by-step explanation:

The substitution of nucleotides in the mouse's DNA may not change its fur color phenotype due to several possible genetic mechanisms. First, the mutation might be silent, meaning that because of the redundancy in the genetic code, the substitution does not change the amino acid sequence of the protein responsible for fur color. Second, the mutation could be non-consequential because the amount of gene product produced by the wild-type allele is sufficient to determine the fur phenotype, exhibiting a form of complete dominance.

Also, it is possible that the fur color is dependent on multiple genes through epistasis, where one gene can mask the effect of another gene at a different locus. In such a case, the presence of other alleles can compensate for the change in one nucleotide pair, hence maintaining the same phenotype. Lastly, due to genetic robustness, organisms can buffer the effects of mutations and maintain phenotypic stability.

Answer 2

Out of the following given choices;

A. The mouse has a completely different DNA sequence than the other mice.

B. The substituted nucleotide has the same directions as the original nucleotide.

C. Substitutions in the nucleotides of a mouse's DNA never affect their phenotypes.

D. DNA sequences don't determine the color of a mouse's fur.

The answer is B. Most probably, the nucleotide substitution did not translate to a change in the amino acid sequence in the translated protein. As you may be aware, most amino acids are coded by more than one codon. For example, Leucine is coded for by CTT, CTC, CTA, CTG, TTA, TTG. Therefore, a substitution, that causes a change to either one of the sequences will not change the amino acid.