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Chapter 15: The Eukaryotic Cell Cycle, Mitosis, and Meiosis (Larissa)

Page history last edited by Larissa-Helen Mahaga-Ajala 13 years, 5 months ago

A.  Daily Blog

The subjects of this chapter were the eurkaryotic cell cycle, mitotic cell division, meiosis and sexual reproduction, and variation in chromosome structure and number.  


Cell division is the means by which cell reproduce.  It is a highly regulated process.  There are two types of eukaryotic cell division: mitosis and meiosis.  Mitosis creates two diploid, identical, daughter cells.  Meiosis creates four haploid cells that aren't identical to each other.  


Humans have 23 pairs of chromosomes, 22 of which are autosomes and 1 of which are sex chromosomes.  Humans and their somatic cells are diploid (have 23 pairs of chromosomes).  Human gametes are haploid (have 23 chromosomes).  Homologous chromosomes are part of the same pair of chromosomes.  Usually they are about the same size and contain the same genetic information.  


The cell cycle has four phases: G1, S, G2, and M.  Also, there is G0, which a cell only goes to when it wants to postpone division or never divide again.  Both external and internal factor affect a cell's decision to divide.  Some examples of external factors are environmental conditions and signalling molecules.  Some examples of internal factors are cell cycle control molecules and checkpoints.  


Checkpoints are points in the cell cycle that the cell is checked for any abnormalities.  If a cell's DNA wasn't copied properly for instance, then the cell won't go on to divide.  Cyclin dependent kinases are responsible for a cell's advancement through the cell cycle.  They must bind to a cyclin to be activated.  The formation of a cyclin-cdk complex allows the cell to move through through checkpoints.  There are checkpoints in G1, G2, and M phases.  


B.  Useful Materials



This picture shows crossing over between homologous chromosomes.  This helps create genetic variation.  



Above is an illustration of mitosis.  At the end of this process there are 2 identical, diploid, daughter cells.    Above is an illustration of meiosis.  At the end of this process there are 4 haploid cells.   


A Sri Lankan Child with 49, XXXXY Syndrome 

Pentasomy 49, XXXXY was previously thought of as a Klinefelter variation.  The first thing that doctors look for is ambiguous genitalia.  Then, after karyotyping, a patient is diagnosed with the disorder.  The patient will have mental retardation, facial dysmorphisms, and a combination of cardiac, skeletal, and other malformations.  This doesn't happen very often.  



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