How are viruses used in gene therapy?
a. to attack the immune system
b. to carry new genes into cells
c. to infect disease-causing bacteria
d. to kill cancer cells that have "suic*de genes"

B. certain viruses are used as vectors because they can deliver the new gene by infecting the cell. the viruses are modified so they can't cause diseases when used in people.

Karyotype refers to the visual appearance and number of the chromosomes in the cell nuclei of a species or an organism. It is known that there are 46 chromosomes in a usual nucleus of a human that comprises 23 pairs of chromosomes. Of these, one pair is considered as sex chromosomes.  

In females, the sex chromosomes are XX, while in males, the sex chromosomes are XY. So, the karyotype of a human male would comprise 22 pairs of autosomal chromosomes, an X chromosome, and a Y chromosome.