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Cell division and reproduction process explained.
Typology: Schemes and Mind Maps
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Specialized diploid cell splits in half twice and produces four separate cells
Cells are able to reproduce themselves Reproduction allows organisms to develop, grow, heal, and stay alive
DNA is organized into chromosomes
Mitosis allows one cell with 46 chromosomes to split into two genetically identical cells
Cells with 46 chromosomes are called diploid cells (two sets)
Cells with 23 chromosomes are called haploid cells
Somatic cells have 46 chromosomes grouped into 23 pairs
Mitosis stages:
Metaphase
Anaphase
Prophase
Telophase
Interphase During interphase, the "strings" of DNA are messy and are called chromatin
Cells in between episodes of mitosis (mostly growing)
During mitosis, a set of protein cylinders next to the nucleus (called centrosome) duplicates itself
Centrosomes regulate everything moved around during mitosis
As mitosis occurs, the DNA begins to multiply itself and the cell ends up with two copies of every strand of DNA
After all that, the cell enters the prophase as the "mess" of chromatin coils upon itself to produce thick strands of DNA wrapped around proteins
These are called chromosomes
The duplicates stay attached to the original in a shape that resembles an "X"
These are called the chromatids and they are made up of a left and arm and a right leg and arm
The meetup in the middle is called the centromere
As the chromosomes form, the nuclear envelope disintegrates and the centrosomes go to the opposite ends of the cell and leave behind a trail of protein ropes called microtubules
Microtubules help provide a structure to the cell
Longest phase of mitosis (up to 20 minutes)
Chromosomes attach themselves to the ropey microtubules at their centromeres
Chromosomes are moved around by molecules called motor proteins (two of these proteins on each side of the centromere → centromere- associated protein E)
At the same time, a protein called dynein is pulling the other ends of the ropes near the cell membranes
After being moved around, the chromosomes line up in the middle of the cell (down)
Motor proteins start pulling really hard on the ropes so the X-shaped chromosomes split into their individual chromosomes
As they are detached from one another, they are dragged toward each end of the cell
Each of the new cell's structures is reconstructed
Nuclear membrane reforms and nucleoli form within them + chromosomes go back into chromatin
Crease forms between the new cells and signals the final split
The division between the cells is called cleavage
Cytokinesis
Two new nuclei move apart and the cells separate
Daughter cells
Clones/genetic copies of the original cell
These cells are genetically different from each other
Meiosis goes through the four stages of mitosis but does it twice
Second round includes diploid cells called primary oocytes or primary spermatocytes (depending on the kind of gamete they make)
Variations of the same genes
Pairs of chromosomes
Only have 23 chromosomes
Need each other to combine and complete the 46 chromosomes
Haploid cells
Same as mitosis
Each double chromosome has two chromatids
Prophase I includes two additional steps
Crossover (^) Each double chromosome lines up next to its homolog (mother's version lined up next to father's)
One chromatid from each X gets tangled up with the other X in a process called crossover
Homologous recombination
During crossover, the chromosomes trade sections of DNA
Genetic information being traded is equivalent (both hair color or both eye color - but never eye color WITH hair color, for example)
All four chromatids are now different
Each chromatid will end up in a different sex cell later on
There is one pair of chromosomes that doesn’t always go through the crossover or recombination
That's the 23rd pair and the sex chromosomes
Female: two X chromosomes (which can do the crossover and recombination since they are the same)
X and Y chromosomes are not homologous (don't match up!)
In meiosis, each chromosome lines up next to its homologous pair-partner (that it's already swapped genes with)
Homologous pairs get pulled apart and migrate to either end of the cell
Pretty much the same as mitosis
End of telophase I marks the end of round one
Leaves us with two haploid cells, each with 23 double chromosomes with new, unique combinations
Centromeres still look like X's
The next round begins and the process is the exact same as mitosis except the aim is different
Not to duplicate the double chromosomes but to pull them apart and separate them into single-strand chromosomes
No DNA replication involved in Prophase II
Instead, the DNA just clumps up again into chromosomes and the infrastructure for moving them, the microtubules are put back into place In metaphase II, the chromosomes are moved into alignment into the middle of the cell
In anaphase II, the chromatids are pulled apart into single chromosomes
Chromosomes uncoil into chromatin and the crease- forming cleavage in the final separation of cytokinesis mark the end of Telophase II