Biology » Modern Understandings of Inheritance » Chromosomal Basis of Inherited Disorders

Summarizing Chromosomal Basis of Inherited Disorders


The number, size, shape, and banding pattern of chromosomes make them easily identifiable in a karyogram and allows for the assessment of many chromosomal abnormalities. Disorders in chromosome number, or aneuploidies, are typically lethal to the embryo, although a few trisomic genotypes are viable. Because of X inactivation, aberrations in sex chromosomes typically have milder phenotypic effects. Aneuploidies also include instances in which segments of a chromosome are duplicated or deleted. Chromosome structures may also be rearranged, for example by inversion or translocation. Both of these aberrations can result in problematic phenotypic effects. Because they force chromosomes to assume unnatural topologies during meiosis, inversions and translocations are often associated with reduced fertility because of the likelihood of nondisjunction.



individual with an error in chromosome number; includes deletions and duplications of chromosome segments


any of the non-sex chromosomes

chromosome inversion

detachment, 180° rotation, and reinsertion of a chromosome arm


individual with the appropriate number of chromosomes for their species


photographic image of a karyotype


number and appearance of an individuals chromosomes; includes the size, banding patterns, and centromere position


otherwise diploid genotype in which one chromosome is missing


failure of synapsed homologs to completely separate and migrate to separate poles during the first cell division of meiosis


inversion that occurs outside of the centromere


inversion that involves the centromere


individual with an incorrect number of chromosome sets


process by which one segment of a chromosome dissociates and reattaches to a different, nonhomologous chromosome


otherwise diploid genotype in which one entire chromosome is duplicated

X inactivation

condensation of X chromosomes into Barr bodies during embryonic development in females to compensate for the double genetic dose

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