Chromosomes
<p><b>A chromosome</b> is packaged and organized chromatin, a complex of macromolecules found in cells, consisting of DNA and protein. The main information-carrying macromolecule is a single piece of coiled double-stranded DNA, containing many genes, regulatory elements and other <i><b>noncoding DNA</b></i><b>.</b> The DNA-bound macromolecules are proteins, which serve to package the DNA and control its functions. Chromosomes vary widely between different organisms. Some species also contain <b>plasmids</b>  or other <b>extrachromosomal DNA</b>.
 
Compaction of the duplicated chromosomes during cell division (mitosis or meiosis) results either in a four-arm structure (pictured to the right) if the <b>centromere</b> is located in the middle of the chromosome or a two-arm structure if the <b>centromere</b> is located near one of the ends. Chromosomal recombination during meiosis and subsequent sexual reproduction plays a vital role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe and die, or it may unexpectedly evade <b> (see below) </b>leading to the progression of cancer.
 
In prokaryotes (see <b>nucleoids</b>) and viruses, the DNA is often densely packed and organized. In the case of <b>archaea by homologs to eukaryotic histones,</b> in the case of bacteria by <b>histone-like proteins.</b> Small circular genomes called <b>plasmids</b> are often found in bacteria and also in mitochondria and <b>chloroplasts,</b> reflecting their bacterial origins.
 
 
<img src="/44e15c34-5d97-5813-836f-7616a8fa66c8.png"/>
 
 
 
<img src="/41011f1d-c226-53c7-bad5-ce6a8ce3ba1f.png"/>
 
<b>Chromosome Numbers</b>
Each organism has a distinct number of chromosomes, in humans, every cell contains 46 chromosomes. Other organisms have different numbers, for instance, a dog has 78 chromosomes per cell.
Somatic Cells - body cells, such as muscle, skin, blood ...etc. These cells contain a complete set of chromosomes (46 in humans) and are called <b>DIPLOID.</b>
Sex Cells - also known as gametes. These cells contain half the number of chromosomes as body cells and are called <b>HAPLOID</b>
Chromosomes come in pairs, called Homologous Pairs (or homologs). Imagine homologs as a matching set, but they are not exacly alike, like a pair of shoes.
Diploid cells have 23 homologous pairs = total of 46
Haploid cells have 23 chromosomes (that are not paired) = total of 23
 
<b>Homologous Chromosomes</b>
 
<img src="/08661269-d75e-5822-be4e-5d8fd70c44ff.png"/>
<b>Apoptosis.  </b>Takes place at a high rate e.g. sculpting a mouse paw, it forms it by killing waste cells. e.g. Tadpole to frog.  
 
 <img src="/50140414-f417-5df2-ae30-157a1134b63a.png"/>    <img src="/924e10ef-ff86-54b7-9f1a-351547bcaac1.png"/>   <img src="/2329ba29-ddfa-5ecc-a903-6f8b70b4fa26.png"/>
 
<b>Apoptosis</b>  is a process of programmed cell death that occurs in multicellular organisms.  Biochemical events lead to characteristic cell changes (morphology) and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, chromosomal DNA fragmentation, and global mRNA decay. Between 50 and 70 billion cells die each day due to apoptosis in the average human adult. For an average child between the ages of 8 and 14, approximately 20 billion to 30 billion cells die a day. There are two pathways, intrinsic and extrinsic. 
 
<img src="/71d515cc-e94c-5f9a-b150-e7a65f0fbd33.png"/>
 
 
 
 
 
 
 
 
 
 
 </p>