Term
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Definition
| - alterations to chromosome structure or changes in the number of copies of chromosomes in a cell – changes in a chromosome region encompassing multiple genes |
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Term
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Definition
individuals that have more than two chromosome sets
i.e. triploids - gene balance within their own genome but are sterile (plants can survive), tetraploids, hexaploids |
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Term
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Definition
| individuals of a normally diploid species that have only one chromosome set (n) – these individuals are sterile (germ cells cannot proceed through meiosis normally because the chromosomes have no pairing partners) |
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Term
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Definition
| failure of the normal segregation of homologous chromosomes or chromatids to opposite poles at meiotic or mitotic divisions – two chromosomes or chromatids incorrectly go to one pole and none to the other (more common as meiotic) |
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Term
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Definition
changes in parts of chromosome sets (abnormal chromosome number); an individual organism whose chromosome number differs from wild type by part of a chromosome set (generally only one chromosome or a small number of chromosomes) ; result mainly from nondisjunction in a parental meiosis
-occur spontaneously at all levels
-almost all aneuploidy progeny will die
-In a diploid, failure of the chromosomes to separate properly at meiosis (meiotic nondisjunction) generates aneuploidy progeny |
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Term
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Definition
(2n–1) – missing one copy of a chromosome – die in utero if for the autosomes but some X-chromosome monosomics are viable
i.e. X-chromosome monosomics: XO - Turner Syndrome
- Much worse than having too many chromosomes because any deleterious recessive alleles present on a monosomic autosome will be automatically expressed |
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Definition
(2n+1) – contain an extra copy of one chromosome – can result in abnormality or death, but can also be viable and even fertile - every time you get a trisomic you also get a monosomic
i.e. XYY, XXX, XXY, Down Syndrome |
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Term
| gene-dosage effect (gene balance) |
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Definition
-the relationship between the number of copies of a gene and the amount of the gene’s product
-aneuploidy genes are out of balance where as euploid genes are not – this difference interferes with the normal function of the genome
-in general the rate of transcription is directly related to the number of DNA templates available
-normal physiology in a cell depends on the proper ratio of gene products in the euploid cell |
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Term
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Definition
| -changes in chromosome structure (DNA breakage is a major cause of these events) |
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Term
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Definition
| -change the gene dosage of a chromosome segment |
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Definition
| a chromosome segment is doubled |
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Definition
| loss of chromosome segment |
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Definition
| reversal in the orientation of a segment within the chromosome |
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Term
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Definition
| a segment of chromosome can be moved to a different chromosome |
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Term
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Definition
| a chromosome that lacks a centromere due to rearrangement - will not be incorporated into either progeny nucleus after mitosis or meiosis – these chromosomes are never inherited |
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Term
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Definition
| - a chromosome with two centromeres due to rearrangement → will often be pulled simultaneously to opposite poles at anaphase forming an anaphase bridge → typically won’t be incorporated into either progeny cell |
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Term
| nonallelic homologous recombination (NAHR) |
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Definition
| crossing over between repetitive (duplicated) DNA segments |
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Term
| Reciprocal translocations |
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Definition
– to form these, two chromosomes trade a centric fragments created by two simultaneous chromosome breaks
•Genetically, genes on translocated chromosomes act as though they are linked if their loci are close to the translocation break point
•These are diagnosed genetically by semisterility and by the apparent linkage of genes whose normal loci are on separate chromosomes |
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Term
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Definition
| change the chromosomal gene order but do not remove or duplicate any DNA |
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Term
| Why can't mammals be triploid? |
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Definition
| gene balance -> not only sex chromosomes but with autosomal genes its unbalanced because of barr bodies for sex chromosome: has to be 1:2 ratio - triploid totally with XXX - 2 barr bodies so 1:3 ratio - not ok |
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