Mitosis and meiosis

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Mitosis and meiosis


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High Yield Notes

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Mitosis and meiosis

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USMLE® Step 1 style questions USMLE

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A researcher is studying gamete production and oogenesis. She decides to cultivate primary oocytes before ovulation and secondary oocytes before fertilization for her experiment. When she examines these gametes, she will find that the primary oocytes and secondary oocytes are arrested in phases of meiosis, respectively?  

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Mitosis p. 44

griseofulvin p. 197


Pretty much everything alive - from a humble bacteria, to a baby blue whale, has two main goals - to grow and to reproduce.

Our cells are no different. They grow and they reproduce.

But the reproduction part can be done in two distinct ways - mitosis, or meiosis.

Mitosis gives rise to daughter cells that are almost identical to the parent cell in terms of their genetic information.

Whereas in meiosis the daughter cells or gametes, sperm in males and eggs in females, get only half of the genetic information of the parent cell.

These gametes can then pair with completely different gametes to form a cell that’s quite different from the parent cell.

This newly formed cell can then do mitosis to form an entirely new organism.

Mitosis is one part of the cell cycle.

Most of the cell cycle is taken by interphase - which is usual cellular day-to-day activities, including growth, protein synthesis, making new organelles, and so on.

Interphase has three phases: G1, S and G2.

The first phase is called G1.

During G1, the cell gets bigger in preparation for cell division.

At this point the 46 chromosomes look like spaghetti and are called chromatin fibers.

Each chromatin fiber is made of a single copy of the genetic material - called a chromatid.

The second phase is the S phase.

During S phase, each chromatid is copied and pasted so there are still 46 chromosomes, but each chromosomes now has two sister chromatids.

The two chromatids are joined together in a region called the centromere - adding up to 92 chromatids total.

The third phase is G2.

During G2, the cell does some more growing before finally entering mitosis.

Some cells, like neurons, enter what’s called the G0 phase - where they basically continue to live but don’t divide.

But most cells do enter mitosis after G2, and mitosis can be divided into four distinct phases: prophase, metaphase, anaphase, and telophase - and you can remember them as PMAT - a mat that you pee on.


Mitosis is the process of cell division that results in two identical daughter cells, each with the same genetic information as the parent cell. Meiosis is a special type of cell division that produces four genetically diverse daughter cells, each with half the number of chromosomes as the parent cell. This occurs during gametogenesis, which is the formation of eggs and sperm.


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