31.   A human cell has about three billion base pairs of DNA.

32.   A new test that can detect several kinds of cancerous human cells was reported yesterday by scientists from the Johns Hopkins School of Medicine in Baltimore.

33.   A vector is the disabled virus used by gene therapists to insert corrective genes into human cells.

34.   ACT officials said last November that they had combined adult human cells with cow eggs that had been stripped of their nucleus.

35.   ACT researchers are currently continuing their efforts to clone human cells to create embryos from which primitive stem cells can be harvested.

36.   Both reports assert that in laboratory tissue cultures of human cells, one or more of these natural chemicals stop HIV from replicating.

37.   But ethicists say great care must be taken in work involving human embryonic cells.

38.   But human cells can recognize the genes, and regularly make transcripts of the genes whose information is required to make proteins.

39.   But human cells have a gene whose product, called telomerase, can lengthen telomeres.

40.   But inserting genes into human cells in full working order has proved to be exasperatingly difficult.