asexual reproduction occurs by mitosis, it is a careful copying mechanism-meaning all offspring are...
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Sexual vs. asexual reproduction
Asexual reproduction occurs by mitosis, it is a careful copying mechanism-meaning all offspring are always genetically identical to the parent
Sexual reproduction occurs by meiosis and brings enormous potential for genetic variability (but the variability will only occur before fertilization
In humans, there are 8,388,608 distinct distributions per gene
DNA Replication
DNA plays an important role in protein synthesis, but also in cell division
Cells must be able to divide in order the for organisms to grow, reproduce and repair itself
DNA is stored in the form of chromatin-long strands of DNA, jumbled up with proteins, that form a disorganized mess of genetic material
When the cell is ready to divide, the chromatin condenses to form chromosomes
Chromosomes
Chromosomes are the genetic information that is passed from one generation to the next
Made up of coiled DNA Each organisms has its own specific
number of chromosomes (humans have 46)
Chromosomes are not usually visible except during cell division
Chromosomes
A chromosomes’ identical copy of itself is called a chromatid
Each chromatid is attached at an area called a centromere (usually located at the center of the chromatid)
Chromosomes
Cell Types
Multicellular organisms are made up of two kinds of cells: reproductive (sex cells) and somatic (body cells)
Reproductive cells have a single set, termed haploid (n)
Somatic cells have two sets, termed diploid (2n)
When the cell divides the chromosomes must be distributed between the new cells
Cell Cycle
The cell cycle is the sequence of stages through which a cell passes between one cell division and the next
There are two main stages: Interphase and Mitosis
Cell Cycle
Interphase
Interphase is the phase where the cell is performing normal cell functions such as protein synthesis and preparing for cellular division
During this phase a series of events (stages) must occur in order for the cell to grow and divide
The stages are G1, S1, G2 (cell growth, DNA replication, and preparation for mitosis via replication of organelles and increasing the amount of cytoplasm)
Interphase
Cells remain in interphase for long spans of their life
Once interphase is complete, then the cell will start to divide
First the cell will increase its size and produce new proteins and organelles
Then each chromosome is replicated After the cell has completed interphase,
cellular division will occur
Cellular Division
Organisms grow and divide because the cells divide and more cells are present-not because individual cells grow larger, this is called cellular division
Cellular division relies on DNA because it stores and transmit’s the hereditary (genetic) information from one generation to the next
Cells will only grow to a certain size because if they get too big, they will lose their ability to regulate their energy uses and waste production, also the cell’s DNA will not be able to keep up with the workload to keep the cell functioning
Cell Division
Before the cell gets too large, the cell will divide into two daughter cells
All of the cell’s organelles and genetic information will be duplicated before the cell divides
Each of the new daughter cells will have a complete set of genetic information
Cell division reduces the cell’s volume but not its size
It occurs in two stages: Mitosis and Cytokinesis
Mitosis
A type of cell division that generates two daughter cells with identical components of the mother cell
Associated with asexual reproduction-it only requires one parent cell
The division of the nucleus and thus the first stage It is a continuous cycle that most cells will undergo Occurs in most multi-cellular organisms (its called
binary fission in unicellular organisms) It is divided into four phases: Prophase,
Metaphase, Anaphase, and Telophase (PMAT)
Mitosis
Prophase-Prepare
It is the longest stage of mitosis Chromosomes thicken and become
visible with a microscope Nuclear membrane disintegrates Centrioles (small cylindrical bodies) move
to opposite ends of the cell Spindle fibers (microtubules) grow from
the centrioles to the chromosomes to help separate them
Prophase-Whitefish
Prophase-Onion
Metaphase-Middle
Chromosomes form pairs attached by centromeres and will align along the middle of the cell
Metaphase-Whitefish
Metaphase-Onion
Anaphase-Apart
The centromeres split which causes the chromosomes to separate back into individual chromatids
The chromatids will move to opposite poles being pulled apart by the spindle fibers
Anaphase-Whitefish
Anaphase-Onion
Telophase-Two
A nuclear envelope appears around each new set of chromosomes
The nucleolus reappears
Telophase-Whitefish
Telephase-Onion
Cytokinesis
Cyto-cell, kinesis-split Material outside of the nucleus must also
divide Generally beings during telophase This is when the actual cell divides to
form two new cells
Cytokinesis
In animals, cytokinesis occurs when the cell membrane pinches in and divides
In plants, a cell plate forms across the middle of the cell which is then followed by the formation of cell walls on each side
Following cytokinesis, the cell returns to the period of interphase
Cell Growth
Cell growth is usually well controlled Most of the time, cells are at different
stages of cellular division throughout the body and divide at different rates
For example, blood cells grow and divide very rapidly whereas brain cells (neurons) do not
There are some instances of uncontrolled cell growth-Cancer
Cancer
It is a condition in which cells grow and reproduce at a rapid rate and do not respond to the usual controls (cyclins) that limit cellular growth
These large masses of cells are called tumors
When tumors form in the body, they can damage the surrounding tissues
If parts of the tumor breaks off into the body, the cancer can spread