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Question
In humans, which meiotic phase has the longest duration?
In humans, which meiotic phase has the longest duration?
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Solution
The correct option is C Prophase - I in females
A cell cycle is a series of events that take place in the cells as it grows and divides. A cell cycle has two phases; interphase and M-phase or dividing phase.
Interphase comprises of G1, S and G2 phases.
- G1 phase (Gap 1 phase)- It is the interval between mitosis and mitosis, where the cell is metabolically and continuously grows.
- S phase (Synthesis phase )- In this phase, DNA synthesis and replication take place.
- G2 phase (Gap 2 phase)- The cell prepares for mitosis in this stage of interphase.
Interphase is followed by the M-phase.
M-phase is where the cell divides. M-phase starts with nuclear division, corresponding to the separation of daughter chromosomes (karyokinesis) and usually ends with division of cytoplasm (cytokinesis).
Karyokinesis involves four stages- prophase, metaphase, anaphase and telophase.
Prophase- This is the first stage of karyokinesis of M- phase, where condensation of the chromosomes, disintegration of the nuclear envelope occurs. Centrosomes begin to move towards opposite poles of the cell.
Metaphase- This is the second stage of karyokinesis. Complete disintegration of the nuclear envelope marks the start of this phase. Spindle fibre attaches to the kinetochores of a chromosome. The chromosomes are moved to the spindle equator and align in the metaphase plate.
Anaphase - This is the third stage of karyokinesis. Where centromeres split and chromatids separate and move to the opposite poles.
Telophase -This is the final stage of karyokinesis. In this stage decondensation of chromosomes occurs. The nuclear envelope develops around the chromosome cluster. Cell organelles like nucleus, golgi complex etc. reform.
Meiosis involves two sequential cycles of nuclear and cell division called meiosis I and meiosis II but with only a single round of DNA replication. Both the division follows these stages of prophase, metaphase, anaphase and telophase.
The interphase is divided into three further phase
Meiosis IMeiosis IIProphase IProphase IIMetaphase IMetaphase IIAnaphase IAnaphase IITelophase ITelophase II
For a typical human cell with a total cycle time of 24 hours, the G1 phase might last for11 hours, the S phase about 8 hours, the G2 phase about 4 hours and the M phase about one hour.
Oogenesis is the process by which mature female gametes develop from germ mother cells. Oogenesis starts with a germ cell called oogonium( plural oogonia), these cells start mitosis and increase the number.
The oogonial cells start meiotic division, enter into prophase-I and get temporarily arrested at the stage called primary oocytes. Each primary oocyte then gets surrounded by a layer of granulosa cells called as primary follicle. The primary follicles get surrounded by more layers of granulosa cells and a new theca called as secondary follicles. The secondary follicle becomes more organised and surrounded by more follicles called tertiary follicles. At this stage, the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. At the time of birth, all the future eggs are in the prophase stage.
At adolescence,(i.e almost after 10-13 years ) anterior pituitary hormones cause the development of a number of follicles in an ovary, this results in the primary oocyte finishing the first meiotic division. The first meiotic division is unequal. The cell divides with most of the cellular material and organelles going to one cell forming a secondary oocyte; a small cytoplasm with one set of chromosomes going to the other tiny cell called the first polar body, which usually dies. Secondary oocyte further goes into the second round of meiotic division and arrests, but this time at the metaphase-II stage. At ovulation, this secondary oocyte is released and travels toward the uterus through the oviduct. If this cell gets fertilized then the second round of meiosis completes producing a second polar body and a fertilized egg.
So among all the phases of the cell cycle, the cell remains longest in prophase - I of meiosis in females.
A cell cycle is a series of events that take place in the cells as it grows and divides. A cell cycle has two phases; interphase and M-phase or dividing phase.
Interphase comprises of G1, S and G2 phases.
- G1 phase (Gap 1 phase)- It is the interval between mitosis and mitosis, where the cell is metabolically and continuously grows.
- S phase (Synthesis phase )- In this phase, DNA synthesis and replication take place.
- G2 phase (Gap 2 phase)- The cell prepares for mitosis in this stage of interphase.
Interphase is followed by the M-phase.
M-phase is where the cell divides. M-phase starts with nuclear division, corresponding to the separation of daughter chromosomes (karyokinesis) and usually ends with division of cytoplasm (cytokinesis).
Karyokinesis involves four stages- prophase, metaphase, anaphase and telophase.
Prophase- This is the first stage of karyokinesis of M- phase, where condensation of the chromosomes, disintegration of the nuclear envelope occurs. Centrosomes begin to move towards opposite poles of the cell.
Metaphase- This is the second stage of karyokinesis. Complete disintegration of the nuclear envelope marks the start of this phase. Spindle fibre attaches to the kinetochores of a chromosome. The chromosomes are moved to the spindle equator and align in the metaphase plate.
Anaphase - This is the third stage of karyokinesis. Where centromeres split and chromatids separate and move to the opposite poles.
Telophase -This is the final stage of karyokinesis. In this stage decondensation of chromosomes occurs. The nuclear envelope develops around the chromosome cluster. Cell organelles like nucleus, golgi complex etc. reform.
Meiosis involves two sequential cycles of nuclear and cell division called meiosis I and meiosis II but with only a single round of DNA replication. Both the division follows these stages of prophase, metaphase, anaphase and telophase.
The interphase is divided into three further phase
Meiosis IMeiosis IIProphase IProphase IIMetaphase IMetaphase IIAnaphase IAnaphase IITelophase ITelophase II
For a typical human cell with a total cycle time of 24 hours, the G1 phase might last for11 hours, the S phase about 8 hours, the G2 phase about 4 hours and the M phase about one hour.Oogenesis is the process by which mature female gametes develop from germ mother cells. Oogenesis starts with a germ cell called oogonium( plural oogonia), these cells start mitosis and increase the number.
The oogonial cells start meiotic division, enter into prophase-I and get temporarily arrested at the stage called primary oocytes. Each primary oocyte then gets surrounded by a layer of granulosa cells called as primary follicle. The primary follicles get surrounded by more layers of granulosa cells and a new theca called as secondary follicles. The secondary follicle becomes more organised and surrounded by more follicles called tertiary follicles. At this stage, the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. At the time of birth, all the future eggs are in the prophase stage.
At adolescence,(i.e almost after 10-13 years ) anterior pituitary hormones cause the development of a number of follicles in an ovary, this results in the primary oocyte finishing the first meiotic division. The first meiotic division is unequal. The cell divides with most of the cellular material and organelles going to one cell forming a secondary oocyte; a small cytoplasm with one set of chromosomes going to the other tiny cell called the first polar body, which usually dies. Secondary oocyte further goes into the second round of meiotic division and arrests, but this time at the metaphase-II stage. At ovulation, this secondary oocyte is released and travels toward the uterus through the oviduct. If this cell gets fertilized then the second round of meiosis completes producing a second polar body and a fertilized egg.
So among all the phases of the cell cycle, the cell remains longest in prophase - I of meiosis in females.
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