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Flashcards in Genetics (Part III) Deck (139)
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What is euploid?

any exact multiple of the haploid number of chromosomes (23)


What is aneuploidy?

if an error occurs in meiosis or mitosis and a cell acquires a chromosome complement that is not the exact multiple of 23


what are the 2 usual causes of aneuploidy?

nondisjunction and anaphase lag


what happens during nondisjunction?

during gametogenesis, the gametes formed either have an extra chromosome or one less chromosome


what happens during anaphase lag?

one homologous chromosome in meiosis or one chromatid in mitosis lags behind and is left out of the cell nucleus; the result is one normal cell with monosomy


what is mosaicism?

mitotic errors in early development give rise to two or more populations of cells with different chromosomal complement


what are ring chromosomes?

when a break occurs at both ends of a chromosome with fusion of the damaged ends


what is an example of a ring chromosome?

46 XY,r(14)


what is inversion of chromosomes?

rearrangement that involves 2 breaks within a single chromosome with reincorporation of that inverted intervening segment


what are the two different types of inversion of chromosomes can you have?

pericentric and paracentric


what is pericentric inversion?

when the breaks are on opposite sides of the centromere


what is paracentric inversion?

inversion involving only one arm of the chromosome


what are isochromosomes?

when one arm of a chromosome is lost, the remaining arm is duplicated--> results in a chromosome that contains 2 short arms only or 2 long arms only


What is translocation?

when a segment of one chromosome is transferred to another chromosome


What are the two different types of translocations?

balanced reciprocal and robertsonian/centric fusion


what are robertsonian translocations?

translocation between 2 acrocentric chromosomes


where do the breaks in the chromosomes typically occur with robertsonian translocations?

closer to the centromeres of each chromosome


what is the result of a robertsonian translocation?

transfer of segments--> 1 very large chromosome and 1 extremely small one; the small one typically is lost


what is the association with robertsonian translocations and trisomy 21?

approximately 3-4% of trisomy 21 cases are caused by robertsonian translocation, in which the q arm of chromosome 21 is translocated onto another chromosome


what is the result of the robertsonian translocation of chromosome 21?

the fetus has 46 chromosomes but 3 copies of the long arm of chromosome 21


What are the typical features of trisomy 21 patients?

typical facies with epicanthal folds and slanted palpebral fissures; single palmer crease


what is the most common chromosomal disorder?

down syndrome


what is the most common cause of trisomy 21?

meiotic nondisjunction; parents have a normal karyotype


in 4% of cases with down syndrome, robertsonian translocations occurred. What is found with these cells?

the genetic material normally found on long arms of two pairs of chromosomes is distributed among only 3 chromosomes


What is the main associated risk with trisomy 21 patients?

40% of trisomy 21 patients have congenital heart disease


what is the most common congenital heart disease seen with trisomy 21 patients?

atrioventricular septal defects (AVSD)


what follows AVSD in the line of congenital heart disease associated with trisomy 21?

VSD, then ASD, then tetralogy of fallot


What is responsible for the majority of the deaths in infancy and early childhood in patients with trisomy 21?

the cardiac abnormalities


What are trisomy 21 patients at increased risk of developing?

acute leukemia


trisomy 21 patients have a 20x increased risk of developing what leukemia?

acute B lymphoblastic leukemia