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| [Klinefelter syndrome] | a condition caused by a two x chromosomes and one y chromosome (47,xxy); characterized by male development, problems with fertility and some mild learning difficulties.
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| [Karyotype] | a picture of an individual's chromosomes arranged in a standard format. the 23 pairs are organized according to size, location of the centromere and the patterns of the dark and light bands.
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| [Isodisomy] | one of two types of uniparental disomy (the other is heterodisomy, defined above); when both copies of a particular chromosome are inherited from the same parent, but they are copies of the same chromosome (each loci has 2 identical alleles). |
| [Isochromosome] | anabnormal chromosome with a centromere and two identical arms, e.g. two q arms versus a p arm and a p arm.
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| [In vitro fertilization (IVF)] | the process where an egg is fertilized with a sperm outside of the body and then transplanted into a woman's uterus.
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| [Inversion] | when a chromosome breaks in two places, the segment may flip over and rejoin, creating an inverted section.
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| [Insertion] | the additionof a piece of chromosomal material into a place on a chromosome where it is not normally found.
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| [Inner cell mass] | after fertilization, the conceptus begins to divide mitotically (each 2 daughter cells identical to the parent cell). the cells begin to differentiate into trophoblast cells (defined below) and the inner cell mass, creating a blastocyst. the inner cell mass will eventually become the embryo and subsequent fetus. |
| [Imprinting] | when agene or part of a chromosome is "turned off" depending on which parent it was inherited from. during the development of the sperm or egg some genes or parts of chromosomes are "paternally stamped" when inherited from the father and some are "maternally stamped" when inherited from the mother.
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| [Implantation] | approximately 6-8 days after fertilization, the trophoblast cells of the blastocyst attach themselves to the endometrial lining of the uterus, and the placenta begins to form. |
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