Hi Miss Teong! :) Sorry for bothering you but, Ive been reading through the meosis lecture notes and im confused at the prophase stage. Like, how come only meosis has crossing over and does this always happen? and also, why are there suddenly non-sister chromatids ? thanks :D
Let me answer your second question first as its linked to the first question. Sister chromatids are formed after DNA replication, where the two DNA molecules are joined together at the centromere. Sister chromatids are genetically identical since they are duplicated. Hence sister chromatids originate from EITHER the father OR the mother.
On the other hand, non-sister chromatids are chromatids of a pair of homologous chromosomes. Meaning that one chromatid originate from the father and one chromatid originate from the mother. Hence they are not genetically identical. Refer to the diagram in the lecture notes.
Now for your first question on crossing over, you are absolutely right. Crossing over (exchange of corresponding section of DNA) occurs between non-sister chromatids only during prophase I of meiosis (and not mitosis). Before I give you the answer, you should probably think through this yourself. Compare the difference of prophase during mitosis and the prophase I of meiosis. Is there a difference at how the chromosomes are arranged? This difference in arrangement would then allow crossing over to occur.
yes i believe we didn't have time to copy this on Tues. But please understand guys (i've had requests from other students as well) that I won't be putting ALL the tutorial answers up on the blog as it would defeat the purpose of listening in class. For example, not all teachers show the suggested solutions in class as well. So i'll be using some form of discretion here. :)
The answer to structured Q2d is the description of the phagocytosis process to bring large insoluble particles into the cell. Make sure you understand what the terms in capital letters mean, otherwise you are not doing your SDL well.
- The plasma membrane INVAGINATES to form a flask-like depression, forming PSEUDOPODIA which engulf the insoluble particles through PHAGOCYTOSIS, with the expenditure of ATP. - The neck of the flask closes forming a PHAGOCYTIC VACUOLE which moves into the cell, leaving the cell membrane to REJOIN.
Hi Miss Teong! :)
ReplyDeleteSorry for bothering you but, Ive been reading through the meosis lecture notes and im confused at the prophase stage. Like, how come only meosis has crossing over and does this always happen? and also, why are there suddenly non-sister chromatids ? thanks :D
Hi Zahidah, no worries. Great question.
DeleteLet me answer your second question first as its linked to the first question. Sister chromatids are formed after DNA replication, where the two DNA molecules are joined together at the centromere. Sister chromatids are genetically identical since they are duplicated. Hence sister chromatids originate from EITHER the father OR the mother.
On the other hand, non-sister chromatids are chromatids of a pair of homologous chromosomes. Meaning that one chromatid originate from the father and one chromatid originate from the mother. Hence they are not genetically identical. Refer to the diagram in the lecture notes.
Now for your first question on crossing over, you are absolutely right. Crossing over (exchange of corresponding section of DNA) occurs between non-sister chromatids only during prophase I of meiosis (and not mitosis). Before I give you the answer, you should probably think through this yourself. Compare the difference of prophase during mitosis and the prophase I of meiosis. Is there a difference at how the chromosomes are arranged? This difference in arrangement would then allow crossing over to occur.
Let me know if you still have any problems. :)
Oh, I get it now. Thanks a tonne!! XD
DeleteMs Teong,
ReplyDeleteCould you upload the last part of the last question of transport across cell membrane tutorial? I didn't finish copying in class yesterday
Hi Celestine,
Deleteyes i believe we didn't have time to copy this on Tues. But please understand guys (i've had requests from other students as well) that I won't be putting ALL the tutorial answers up on the blog as it would defeat the purpose of listening in class. For example, not all teachers show the suggested solutions in class as well. So i'll be using some form of discretion here. :)
The answer to structured Q2d is the description of the phagocytosis process to bring large insoluble particles into the cell. Make sure you understand what the terms in capital letters mean, otherwise you are not doing your SDL well.
- The plasma membrane INVAGINATES to form a flask-like depression, forming PSEUDOPODIA which engulf the insoluble particles through PHAGOCYTOSIS, with the expenditure of ATP.
- The neck of the flask closes forming a PHAGOCYTIC VACUOLE which moves into the cell, leaving the cell membrane to REJOIN.
Hope that is clear!