Biology 9700 · AS & A Level · Natural and artificial selection
Natural and artificial selection — practice question
Myostatin is a protein made in mammalian skeletal muscle cells. It travels in the bloodstream and acts on muscle tissue to reduce any further differentiation and growth.
In thoroughbred racehorses, a mutation caused by the substitution of a single nucleotide has been found in the MSTN gene that codes for myostatin. At this mutation site, the DNA nucleotide is either a cytosine (C) base or a thymine (T) base, so race horses have three possible genotypes for this mutation: CC, CT or TT.
(a)[2]
At 2 years old, racehorses with the $MSTN\ CC$ genotype have more muscle mass than those with the $TT$ genotype. Suggest why this difference occurs.
(b)
Racehorses that had won over different distances were examined to find their $MSTN$ genotype. The findings are shown in Fig. 2.1.
(c(i))[2]
Modern thoroughbred racehorses are the outcome of many years of artificial selection. Explain what is meant by artificial selection.
(c(ii))[2]
Explain how genetic tests for the MSTN genotype may aid the selective breeding of racehorses.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “a C base in DNA changes an amino acid in myostatin” …