Cytogenetics

cytogenetics

the study of chromosomes and genomic structure, function, and variation and their role in human disease and heredity

meiosis start in females

before birth, arrests, then puberty

meiosis start in males

at puberty

maternal age aneuploidy risk

proteins are not as strong as age increases due to meiotic arrest between birth and puberty; proteins cannot separate chromosomes as well

euploid

normal chromosome number

aneuploid

abnormal number of chromosomes

polyploid

abnormal number of chromosome sets

common aneuploidies

XXY

45,X

+21

+18

+13

+16

Klinefelter syndrome

47, XXY

Turner syndrome

45,X

Edwards syndrome

47,XY,+18

Patau syndrome

47,XY,+13

polyploidy causes

dispermy

failed polar body extrusion

failure of first cell division

karyotype nomenclature

chromosome number, sex chromosome constitution, abnormalities present, multiple cell lines

reciprocal translocation

mutual exchange after breaks (balanced)

most have no phenotype

can lead to gene fusions

alternate segregation

leads to balanced gametes

adjacent segregation

leads to unbalanced gametes with partial trisomy/monosomy zygotes

acrocentric chromosomes

13, 14, 15, 21, 22

robertsonian translocation

translocation between acrocentric chromosomes, short arms are lost while long arms fuse

quadrivalent

forms during meiosis I for balanced translocation carriers

trivalent

forms during meiosis I for Robertsonian translocations

offspring empiric risk for homologous robertsonian carriers

100%

pericentric inversion

inversion that includes the centromere

paracentric inversion

inversion within the same chromosome arm

add

indicates material of unknown origin

regions of homozygosity

long runs of DNA very similar to each other