Chromosome Numerical Abnormalities Flashcards
Term for number of homologous chromosome sets present in a cell or organism
Ploidy (n)
Define human haploidy, diploidy and polyploidy
Haploid = n = 23
Diploid = 2n = 46
Triploidy = 3n = 69
etc.
Define aneuploidy and euploidy
Euploidy - exact multiple of haploid set of chromosomes
Aneuploidy - incomplete haploid set - abnormal chromosome numbers (45, 47 etc)
Most common parent and phase of meiosis for aneuploidy?
Maternal meiosis I
Incidence of ALL chromosome abnormalities in newborns?
1 in 150
Incidence of ALL aneuploidy in newborns?
1 in 250
Incidence of X and Y aneuploidy in newborns?
1 in 475
Incidence of autosome aneuploidy in newborns?
1 in 700
Incidence of balanced structural abnormalities in newborns?
1 in 500
Incidence of ALL structural abnormalities in newborns?
1 in 375
Incidence of unbalanced structural abnormalities in newborns?
1 in 1600
Incidence of trisomy 21 in newborns?
1 in 700 (to 1,000) livebirths
Incidence of trisomy 18 in newborns?
1 in 6000 (to 10,000)
Incidence of trisomy 13 in newborns?
1 in 10,000 (to 16,000)
Most common trisomy in miscarriage?
Trisomy 16 - 80%
___% of sperm and ___% of oocytes show chromosome abnormalities
10% of sperm
20-25% of oocytes - aneuploidy > polyploidy > structural abnormalities
Four tolerated aneuploidies in conceptus?
45,X and trisomies 16, 21 and 22
Three tolerated autosomal trisomies?
13, 18, 21 (also most common cause of stillbirths)
Cause of 95-99% of SABs?
Turner syndrome 45, X
Crossing over occurs in what phase of Meiosis?
Prophase I
4c, 2n
At the end of male meiosis I what is the ploidy?
2c, 1n
haploid with 2 copies
At the end of male meiosis II what is the ploidy?
1c, 1n
haploid with 1 copy
5 phases of prophase I?
leptotene - beginning of chromosome condensation , telomeres touch nuclear membrane
zygotene - homologs pair and synapsis
pachytene - crossing over
diplotene - homologs separate, tethered by chiasma
diakenesis - separation of homologs
Eggs are suspended in which meiosis phase until fertilization?
Prophase I