title: Robertsonian translocation and an extra microchromosome: aetiology and effect on meiotic segregation.
abstract: A familial Robertsonian translocation accompanied by a marker chromosome t(14q;21q), + iso dic (?14?21)(pter----q11.1) is described. The evolution of the marker is considered in relation to a model proposed by ultrastructural studies of acrocentric bivalents for the formation of Robertsonian-type translocations. Previous reports have suggested that a marker chromosome may be of pathogenetic importance for non-disjunction of chromosome 21. The effect of the marker chromosome on meiotic segregation in the family described and its implications upon genetic counselling are considered.
mesh_terms: D000032:Abortion, Therapeutic; D002883:Chromosomes, Human, Pair 14 / Q000648:ultrastructure*; D002891:Chromosomes, Human, Pair 21 / Q000648:ultrastructure*; D004314:Down Syndrome / Q000175:diagnosis / Q000235:genetics*; D005260:Female; D005817:Genetic Counseling; D005819:Genetic Markers; D006801:Humans; D007231:Infant, Newborn; D014178:Translocation, Genetic
chemical_list: D005819:Genetic Markers