If you read any of the many blogs or news sources that deals with bioethics, then you will have heard of the story from the BBC that a British fertility doctor has successfully performed eugenics via in vitro fertilization. He tested embryos for a gene that is associated with an increased risk of breast cancer, and implanted only those embryos that were pure enough to meet his standards; the rest were killed (euphemistically, "discarded"). What was really remarkable about the story was the ridiculous attempt to redefine standard medical terminology to make the act more palatable. Conception is synonymous with fertilization, but the BBC parroted the doctor in incorrectly claiming that conception is actually synonymous with implantation. This allows the doctors to pretend that the genetic test took place before any human individuals were created by saying it was "pre-conception." For more information, see this post on the blog Mary Meets Dolly.

For the benefit of readers who may encounter mendacious doctors and scientists who deal with beginning-of-life issues, here is a glossary of related terms:

abortifacient

A drug or other substance that induces an abortion. Abortifacients may cause expulsion of the embryo or fetus, killing it, or they may prevent the implantation of an embryo. In the narrowest clinical sense, the latter is not technically the termination of a pregnancy, but it does result in the killing of the embryo.

abortion

The termination of a pregnancy; usually used for terminations before about 20 weeks gestation. Abortions may be spontaneous and natural (in which case they are also called miscarriages) or intentional (in which case they are also called induced abortions). An abortion always results in the death of the embryo or fetus.

adult stem cell

Any stem cell derived from an individual after the embryonic stage of development. Despite the name, they can be obtained from fetuses, umbilical cords, and children as well as from adults. Adult stem cells vary widely in potency. They can be obtained without injuring the donor.

baby

A non-scientific, non-specific term referring to a young human individual. Depending on context, it can refer to a zygote, embryo, fetus, newborn, or older child. Obstetricians routinely refer to embryos and fetuses as "babies" when the pregnancy is wanted, but not if the mother intends to abort the pregnancy. See abortion.

chromosome

A unit of genetic material. Every species has a fixed number of chromosomes.

conception

Synonymous with fertilization.

diploid

Having two copies of each chromosome per cell. In mammals, all cells except gametes are diploid.

egg

Also called an ovum, a female gamete. In humans, eggs are very large cells that are usually produced one at a time.

embryo

An organism from the time of the first cell division to a set point such as birth or hatching. In humans, an individual from the first cell division after conception until eight weeks after conception (ten weeks gestation), at which point it is called a fetus.

embryonic stem cell

A stem cell taken from an embryo. Embryonic stem cells are pluripotent, meaning they can differentiate into almost any tissue type. They are obtained by removing the embryo's inner cell mass, killing the embryo.

eugenics

The practice of attempting to improve the human race by either killing individuals perceived as genetically inferior, preventing such individuals from reproducing, or encouraging increased reproduction for individuals perceived as superior.

fertilization

The union of a haploid egg and a haploid sperm, resulting in a new, independent diploid individual. Fertilization naturally takes place in a woman's Fallopian tube after sperm are introduced through sexual intercourse.

fetus

In humans, an individual from eight weeks after fertilization until birth. A fetus that is near term is indistinguishable from a newborn except in certain physiological characteristics that change at birth, such as the closing of a blood vessel called the ductus arteriosus.

gamete

A haploid reproductive cell whose role is to unite with an opposite-sex gamete to create a new individual. Also called sex cells, they consist of eggs and sperm.

haploid

Having one copy of each chromosome per cell. In mammals, only gametes are haploid; all other cells are diploid.

implantation

The point at which an embryo, at the age of a few days in humans, becomes attached to the lining of the uterus.

in vitro fertilization

Fertilization that takes place outside the human body ("in vitro" literally means "in glass"). In vitro fertilization removes the sex act from reproduction. The zygotes are allowed to develop for several days into embryos, at which time one (or more) is placed inside the mother's body in the hope that it (or they) will undergo implantation, resulting in pregnancy. For practical reasons, it involves the fertilization of multiple zygotes, almost always more than can ever be implanted.

miscarriage

Also called spontaneous abortion, the unintentional termination of a pregnancy as a result of natural causes or, less commonly, accident.

newborn

Also called a neonate, an individual who has very recently been born. A newborn is indistinguishable from a late-term fetus except in certain physiological characteristics related to the loss of the placenta.

pregnancy

In mammals, including humans, the carrying of one or more embryos or fetuses in the uterus. In clinical terms, pregnancy begins at implantation, though the embryo exists as a separate individual in the mother's body before implantation. Thus pregnancy begins after the beginning of an individual human life.

sperm

A male gamete. In humans, sperm are small, motile cells that are produced daily in very large numbers by men's bodies.

stem cell

A cell capable of reproducing indefinitely, and usually capable of developing into one of several types of tissue. Stem cells are classified by "potency," that is, how many different types of tissue they can become. Stem cells are found in developing embryos, in umbilical cords, and in various other tissues such as bone marrow.

zygote

A brand-new, single-celled individual from fertilization until the first cell division, at which point it is called an embryo. The zygote stage in humans is very brief; it experiences the first cell division and becomes an embryo even before implantation.