How can reduce the number of Statements for this code in c#

Question

Hi, how can I optimize my code? Reduce the number of lines(Statements) 

 

private void button1_Click(object sender, EventArgs e)

{

string[] seq1 = { "A", "C", "G", "T", "A", "C", "A", "G","T","G" };

string[] seq2 = { "T", "A", "C", "A", "C", "G","A","A","G","T" };

string[] res1 = new string[seq1.Length];

string[] res2 = new string[seq1.Length];

for (int i = 0; i <= 4; i++)

{

res1[i] = seq1[i];

res2[i] = seq2[i];

textBox1.Text +=" "+ res1[i];

textBox2.Text +=" "+ res2[i];

}

for(int i = 5; i < seq1.Length; i++)

{

if (seq1[i] == "T" )

{

res1[i] = "A";

}

else

if (seq1[i] == "A" )

{

res1[i] = "T";

}

else

if (seq1[i] == "C" )

{

res1[i] = "G";

}

else

if (seq1[i] == "G" )

{

res1[i] = "C";

}

textBox1.Text += res1[i]+" ";

}

for (int i = 5; i < seq2.Length; i++)

{

if (seq2[i] == "T")

{

res2[i] = "A";

}

else

if (seq2[i] == "A")

{

res2[i] = "T";

}

else

if (seq2[i] == "C")

{

res2[i] = "G";

}

else

if (seq2[i] == "G")

{

res2[i] = "C";

}

textBox2.Text += res2[i] + " ";

}

}