phelanphys3e

KNOWLEDGE YOU CAN USE

Can You Select the Sex of Your Baby? (Would You Want To?)

Question 6.11

Q: Given our knowledge of the behavior of the X and the Y chromosomes, is it more likely that these sex-selection techniques involve manipulations of sperm or of eggs? Why? Because all eggs have X chromosomes, the X chromosome doesn’t play a role in determining the sex of a baby. Instead, the fertility clinics must somehow sort and separate sperm cells based on whether they carry an X or a Y chromosome (men produce approximately equal numbers of each).

Question 6.12

Q: What feature of sperm must be used in separating them? This process must be based on a way of distinguishing between sperm carrying an X chromosome and sperm carrying a Y chromosome. After the two types of sperm are distinguished, they must then be separated. Sperm with the desired sex chromosome are then used to fertilize the woman’s egg (which may be done within her body, using artificial insemination, or in a Petri dish, after which a fertilized embryo is transferred into the woman’s reproductive tract).

Question 6.13

Q: What techniques might make it possible to separate sperm with an X chromosome from those with a Y chromosome? One method involves determining, by weighing sperm, which cells have more DNA. The heavier sperm must be carrying the X rather than the Y chromosome because the X is so much larger. Another method is to add a fluorescent dye to sperm that temporarily attaches to DNA. Because sperm with an X chromosome have more DNA, more of the dye attaches to them and they are more fluorescent. A machine then sorts the sperm one by one, and at ovulation, insemination is performed using the sperm with the desired sex chromosome.

Question 6.14

Q: Does it work? The technique is still fairly new, but initial results suggest that the procedures have a success rate of 70% to 90%.

Question 6.15

Q: Concerns for you to ponder. What are the ethical concerns raised by selecting the sex of one’s baby? Are there some circumstances in which such a selection would be more acceptable than in others? Would it be acceptable to select for a baby with one eye color versus another? Why would that process be more difficult than selecting for sex?