Campbell and Reece 8th edition

[Stephen1993]

thank you for that

very quickly
in meiosis
is there crossing over between the sex chromosomes? XX chromosomes in females and XY chromosomes in males?

pg 242
Loss of cell cycle controls in cancer cells

"They may make a required growth factors themselves, or they may have an abnormality in the signalling pathway that conveys the growth factor's signal to the cell cycle control system even in the absence of that factor."
What does the last part of the sentence mean?

thank you