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| [Infertility] | the state of being unable to produce offspring; in a woman it is an inability to conceive; in a man it is an inability to impregnate. |
| [azoospermia] | absence of motile (and hence viable) sperm in the semen. |
| [Zygote] | a fertilized egg. through cell division the zygote develops into a multicellular embryo and then into a fetus.
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| [Y chromosome] | a sex chromosome; typical males carry one y and one x chromosome.
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| [X chromosome] | a sex chromosome; typical females carry two x chromosomes.
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| [XYY syndrome] | a genetic condition in males with extra y chromosome (in 1 in 1000 male births). these individuals are tall in stature (over 6') and may experience problems with fertility, developmental delay, learning problems.
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| [X-inactivation] | early in the development of a normal female, one of the x-chromosomes in each cell is randomly inactivated. all descendent cells of that cell will have the same x-chromosome inactivated. thus, all females are mosaic for some cells which express the paternal x-chromosome and others with express the maternal x-chromosome.
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| [Villus stroma] | one of two cell types in the inner layer of the chorionic villi of the placenta (the layer closer to the amniotic sac and developing fetus). trophoblast cells make up the outer later of the chorionic villi.
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| [Uterus] | the female organ in which the fetus develops into a baby; also known as the womb.
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| [Uniparental disomy] | when both members of a chromosome pair are inherited from one parent rather than one from each parent. uniparental disomy may be maternal or paternal.
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