Anaphase promoting complex (APC) is a protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in a human cell, which of the following is expected to occur?
(a) Chromosomes will not condense
(b) Chromosomes will be fragmented
(c) Chomosomes will not segregate
(d) Recombinantion of chromosome arms will occur
(c) If anaphase promoting complex is defective in a human cell, the chromosomes will not segregate during anaphase of mitosis. APC triggers the transition from metaphase to anaphase by tagging specific proteins for degradation.
Concept Enhancer Anaphase stage of meiosis is characterised by two events
(a) Splitting of centromeres and segregation of chromosomes
(b) Movement of chromatids towards the opposite poles.
DNA replication in bacteria occurs
(a) during S-phase
(b) within nucleolus
(c) prior to fission
(d) just before transcription
(c) The cell cycle is a series of events that take place in cell leading to its division and duplication of its DNA. Bacteria lack a cell nucleus. Due to their primitive nature they lack a well marked S-phase. In bacteria DNA replication occurs before fission.
Concept Enhancer: Bacteria cell cycle is divide into the B,C and D periods. The B period extends from the end of cell division to the beginning of DNA replication. DNA replication occurs during the C period. The D period refers to the stage between the end of DNA replication and the division of bacterial cell into two daughter cells.
Which of the following options gives the correct sequences of events during mitosis?
(b) During mitosis following events occurs as their is condensation of chromosomal material, which takes place at an early prophase stage. During late prophase nuclear membrance disintegrates. Then chromosome get arranged at equator in the metaphase stage. After that splitting of centromere and segregation of chromosomes occur in the anaphase stage. In telophase stage chromosomes move to opposite poles of the cell. It is last stage of mitosis.
During cell growth, DNA synthesis takes place in
(a) S-phase (b) -phase
(c) -phase (d) M-phase
(a) In the cycle of cell division, interphase is the longest phase consisting of , S, -phases. In this phase cell prepares itself for cell division. In S-or synthesis phase DNA duplication (synthesis) takes place.
When cell has stalled DNA replication fork, which checkpoint should be predominantly activated?
(d) Both G2/M and M
(a) stalled forks activate checkpoint signaling and pause replication. Since, G1/S checkpoint checks DNA damage, cells size prior to S-phase (i.e. DNA replication phase). this checkpoint would be activated by stalled DNA replication fork.
Match the stage of meiosis in column I to their characteristic features in column II and select the correct option using the codes given below
Column l Column ll
A. pachyetne 1. pairing of homologous chromosomes
B. Metaphase-l 2. Terminalisation of chaismata
C. Diakinesis 3. Crossing-over takes place
D. Zygotene 4. Chromosomes align at equatorial plate
The correct option:
A B C D
(a) 3 4 2 1
(b) 1 4 2 3
(c) 2 4 3 1
(d) 4 3 2 1
(a) Various phases of meiosis and their characteristic features are
Pachytene - Crossing over takes place
Metaphase-l - Chromosomes align at equatorial plate
Diakinesis - Terminalisation of chiasmata
Zygotene - Pairing of homlogous chromosomes
Hence, option (a) is correct.
Short Trick The question can be easily solved if some one has the perfect idea about the connectivity between pachytene and crossing-over as only option (a) contains this combination.
A cell at telophase stage is observed by a student in a plant brought from the field. He tells his teacher that his cell is not like other cells at telophase stage. There is no formation of cell plate and thus the cell is containing more number of chromosomes as compared to other dividing cells. This would result in
(b) somaclonal variation
(a) Polyploid cells have a chromosome number that is more than double the haploid number e.g. Triticum aestivum (wheat) is a hexaploid(6n)).
Which of the following is not a characteristic feature during mitosis in somatic cells
(a) Disappearance of nucleolus
(b) Chromosome movement
(d) Spindle fibres
(c) Synapsis is pairing of homologous chromosomes. It occurs during zygotene stage of meiosis. The homologous chromosomes come closer leading to cross over in the next stage called pachytene. These are not observed during mitosis.
Spindle fibres attach on to
(a) Kinetochore of the chromosome
(b) centromere of the chromosome
(c) Kinetosome of the chromosome
(d) telomere of the chormosome
(a) Spindle fibres attach to kinetochores of chromosomes during cell division. They help the chromosomes/chromatids to get separated to the two daughter cells, towards opposite poles.
In meiosis crossing over is initiated at
Leptotene - Condensation of chromatin
Zygotene - Synapsis of homologous chromosomes
Pachytene - Crossing over
Diplotene - Dissolution of synaptonemal complex and appearance of chiasmata
Diakinesis - Terminalisation of chiasmata