recap

42.5 recap

Controlling fertility is an important aspect of modern human life. Decreasing the probability of pregnancy is achieved through methods that prevent sperm and egg from meeting and from preventing implantation. Pregnancies can be facilitated through technologies that extract eggs from the ovary and fertilize them in vitro before reintroducing them into the female reproductive tract.

learning outcomes

You should be able to:

  • Describe the relative advantages and disadvantages of different contraceptive methods.

  • Compare contraception and contragestational techniques.

  • Explain how procedures that use genetic analysis and in vitro fertilization (IVF) can help carriers of genetic disease avoid producing afflicted children.

Question 1

Which method of contraception is the only one to offer protection against sexually transmitted diseases (STDs)? Explain your answer.

The condom is the only contraceptive technology that can protect against STDs because if used properly it protects each partner from contact with the body fluids of the other.

Question 2

Both the contraceptive pill (“the pill”) and the contragestational pill (RU-486) involve progesterone signaling. How do their mechanisms of action differ?

The pill delivers a high dose of progesterone that exerts negative feedback on the hypothalamic–pituitary axis to inhibit the production and release of LH and FSH, which are essential for the maturation and release of an egg from the ovary. RU-486 is an antiprogestive drug. During the luteal stage of the menstrual cycle, high levels of progesterone from the corpus luteum maintain the endometrium of the uterus in a receptive condition to receive a blastocyst. Blocking that action of progesterone can prevent implantation of the blastocyst or promote sloughing of the endometrium.

Question 3

How can IVF be used to prevent transmission of a genetic disease?

IVF can be used to prevent transmission of a genetic disease because cells can be taken from the early embryo in culture and analyzed for the suspected defective gene. Only embryos that do not carry the defective gene can then be selected for implantation into the uterus of the mother.

The fertilized egg of a sexually reproducing organism is a single cell containing all the genetic information needed to create a new organism. Chapter 19 introduced some of the molecular aspects of the process of development in multicellular animals. Chapter 43 will describe the physiological and anatomical events of animal development.