Question

Is Down syndrome an error in DNA replication in S phase?

Answer 1

Down syndrome or trisomy 21 occurs when an individual has a third copy of chromosome 21.

It would have to be a stunningly catastrophic error in DNA rep to prevent replication of an entire chromosome - not a simple indel or a point substitution. More likely it results from a failure of chromosome mechanics during mitosis itself resulting in one progeny cell getting an extra copy and the other progeny cell not getting a copy of the entire chromosome.

Answer 2

During the Synthesis Phase (S-Phase), two exactly identical Chromosomes are created. The cell then prevents multiple replications from occurring by loading pre-replication complexes to the DNA at replication origins during the G1-phase, which are dismantled in S-phase as replication begins.

(As I'm typing this, there's already a good answer above)

Down syndrome occurs when there is an extra copy of Chromosome 21, or rather, when multiple replications occur on the genes of Chromosome 21.

Though the S-Phase is also the process where DNA Damage is detected, an error in Replication might be caused if somewhere in the Synthesis phase an abnormal process occurs.

Therefore, It's very likely to be an error in the S-Phase.

Answer 3

To Vernard
I think it shouldnt be an error in S phase, just as what blues said
I get it now, that DNA replication error is usually juz a few errors, but wont be the whole chromosome
so more likely that error does not occur in the S phase but mitosis when the spiltting takes place

Answer 4

good

Answer 5

You're right cmkc109. a huge amount of error has to happen in the S-Phase if it's the case, so later on I thought it would be somewhere in the beginning of the interphase (G1).