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A nullisomic is missing both hromosomes of a homologous pair; so a nullisomic of species II for chromosome N would be 2N-2. (MMOO). Having no copies of a chromosome.
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A monsomic is missing a single chromosome; so a monosomic for species I would be 2n-1 (ABB or AAB). Having only one copy of a chromosome.
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A trisomy requires an extra chromosome; so a trisomic of species II for chromosome M would be 2N+1 (MMMNNOO).
Having three copies of a chromosome.
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A tetrasomic has two extra homolohous chromosomes; so a tetrasomic of species I for chromosome A would be 2N + 2 (AAAABB). Having four copies of a chromosome
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An autotriploid is 3n, with all the chromosomes coming from a single species; so an autriploid of species I would have chromosomes AAABBB. All sets of chromosomes are from the same species. Autopolyploids typically arise from mitotic nondisjunction of all the chromosomes in an early 2n embryo, reslting in an autoterraploid, or from meiotic nondisjunction that results in a 2n gemete fusing with a 1n gamete to form an autotriplod.
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An allotetraploid is 4n, with chromosomes coming from more than one species. An allotetraploid could consist of 2 \n from species I and 2n from species II or any other ratio equalling 4n. |
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| Loss of a portion of a chromosome. Decreases the amount of genetic material on a particular chromosome. |
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| Addition of an extra copy of a portion of a chromosome. Increases the amount of genetic material on a particular chromosome. |
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| A portion of the chromosome is reversed in orientation. Changes the position of DNA sequences on a single chromosome without changing the amount of genetic material. |
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| A portion of the chromosome becomes incorporated into a different (nonhomologous) chromosome. Moves DNA from one chromosome to a nonhomologous chromosome. |
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| Loss or gain of one or more chromosomes so that the chromosome number deviates from 2n or the normal euplod complement. |
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| Gain of entire sets of chromosomes so the chromosome number changes from 2n to 3n (triploid), 4n (tetraploid), and so on. Increase the amount og genetic material for all chromosomes. |
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| The term for a condition where having only one copy of a wild-type gene does not produce a wild-type phenotype in an otherwise diploid organism. For haploinsufficient genes, the relative amounts of gene product is important. |
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Does not include the centromere |
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Robertsonian translocation |
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| The long arms of two acrocentric chromosomes are joined to a common centromere through translocation, resulting in a large metacentric chromosome and a very small chromosome with two very short arms. The very small chromosome may be lost. |
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| caused by spontaneous, random nondisjunction of chromosome 21, leading to trisomy 21. |
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| most frequently arises as a result of Robertsonian translocation of chromosome 21 with another chromosome, usually chromosome 14. Translocation carriers do not have Down syndrome, but their children have an increased incidence of Down syndrom. If the translocated chromosome segregates with the normal chromosome 21, the gamete will have two copies of chromosome 21 and result in a child with familial Down syndrome. |
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| The inheritance of both copies of a chromosome from the same parent. This may arise originally from a trisomy condition in which the early embryo loses one of the three chromosomes, and the two remaining copies are from the same parent. |
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| A condition in which an individual has patches of cells that are generically different from other cells. Mosaicism may arise from mitotic nondisjunction during early embryonic divisions, X-inactivation in a heterozygous female, fusion of two zygotes into a single embryo, and other mechanisms. |
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| The chromosomes of two different species are contained in one individual through the hybridization of two related species followed by mitotic nondisjuntion. Fusion of gametes from two different )but usually related) species results in a hybrid with a haplod set of chromosomes from each parent. If an early embryonic cell then undergoes mitotic nondisjunction and doubles each chromosome, then a fertile 4n allotetraploid individual having two copies of each chromosome from each species may result. |
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