private void btn_Submit_Click(object sender, EventArgs e)
        {
            this.OutputSequences = "";
            if (string.IsNullOrEmpty(this.InputSequences))
            {
                MessageBox.Show("Please do not submit empty content. ");
                return;
            }
            FastaParser       parser       = new FastaParser(this.InputSequences);
            List <FastaEntry> fastaEntries = parser.ParseFasta();

            if (fastaEntries == null)
            {
                switch (this.Countpart)
                {
                case CountpartType.ReverseComplement:
                    this.OutputSequences = SequenceGenerator.ReverseComplementSequence(this.InputSequences);
                    break;

                case CountpartType.Reverse:
                    this.OutputSequences = SequenceGenerator.ReverseSequence(this.InputSequences);
                    break;

                case CountpartType.Complement:
                    this.OutputSequences = SequenceGenerator.ComplementSequence(this.InputSequences);
                    break;

                default:
                    MessageBox.Show("Please choose a counterpart. ");
                    break;
                }
                this.rtx_OutputSequences.Text = this.OutputSequences;
                return;
            }
            foreach (FastaEntry f in fastaEntries)
            {
                switch (this.Countpart)
                {
                case CountpartType.ReverseComplement:
                    f.Sequence = new StringBuilder(SequenceGenerator.ReverseComplementSequence(f.Sequence.ToString()));
                    break;

                case CountpartType.Reverse:
                    f.Sequence = new StringBuilder(SequenceGenerator.ReverseSequence(f.Sequence.ToString()));
                    break;

                case CountpartType.Complement:
                    f.Sequence = new StringBuilder(SequenceGenerator.ComplementSequence(f.Sequence.ToString()));
                    break;

                default:
                    MessageBox.Show("Please choose a counterpart. ");
                    break;
                }
            }
            foreach (FastaEntry entry in fastaEntries)
            {
                this.OutputSequences += entry.ToString();
            }
            this.rtx_OutputSequences.Text = this.OutputSequences;
        }