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DNA and genetics

Deoxyribonucleic acid (DNA)
-Watson and Crick described the structure of DNA molecules.

Watson and Crick model
-The DNA is made up of nucleotides.
-DNA has the same structure in all organisms.
- Each nucleotide is consisted of ---> phosphate group
--->Deoxyribose sugar
--->one of the 4 nitrogenous bases
4 nitrogenous bases : Adenine
Guanine
Cytosine
Thymine




-Nucleotides are organized in a way that makes a double helix.




-The nitrogenous bases pair up in one way where complementary bases are paired.
Adenine pairs up with Thymine ---> A-T rungs
Guanine pairs up with Cytosine ---> G-C rungs

, -Uprights of the ladder like structure(the double helix structure) are made up of
alternating phosphate and sugar groups.

Chromosomes
-Long, thin, thread like structures found in the nuclei of all cells in the human body
that contain a nucleus.
-Each chromosome is one very long DNA molecule wrapped around proteins(histone
proteins)




-In humans the chromosome number is 46.
-Half of 46 chromosomes come from father and the other half from mother.
-Gametes ( sperm , egg) contain 23 chromosomes.