BIOL 311 Lecture Notes - Lecture 4: Y Chromosome, Dna Profiling, Variable Number Tandem Repeat

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Published on 10 Dec 2017
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Gene tic Varia b ility
NOMENCLATURE
- Locus : location of a s ingle nucle otide or a s tre tch of ma ny nucle otide s a nywhe re on a
chromos ome
- Ge ne: coding locus consis ting of a s pe cific DNA s e quence , producing e ithe r a prote in or
functiona l RNA
- Anonymous locus : DNA locus without any a ppa re nt function
GENETIC VARIABILITY AND LOCI
- A polymorphis m is whe n 2 or more diffe re nt DNA s e quence s e xis t at a DNA locus
- Change s in DNA s e que nce a re known a s DNA polymorphis ms
- 3 type s of DNA polymorphisms :
1. Single Nucle otide P olymorphism (S NP )
Mos t common
Re pla cing one nucleotide with a nothe r
Two types :
- Trans ition (P urine to Purine or Pyrimidine to P yrimidine )
- Trans version (Purine to Pyrimidine a nd vice vers a )
3 ca us e s
- Occur whe n DNA polyme ra s e a dds a n incorre ct ba se , which re s ults in a
misma tche d bas e pa ir
- Bas e ta utomeriza tion which fools DNA polyme ra se into a dding a wrong nucleotide
Bas e s have more tha n one ta utomeric form
Beca use DNA is s e mi-cons e rvative, introducing a ba se cha nge ge ts pa s s ed on to
future ge ne ra tions
Ta utomeric forms of purine s a nd pyrimidine s a llow the m to ba s e pa irs with the
“wrong” partne r
What ca us e s ba s e tautome riza tion? Ele ctronic redistribution (like isome rs)
Bas e s can only get a ta utomeric form of a nothe r bas e of the s ame family (i.e .
purine ca n ta utome rize to a ct only a s a nother purine , not a pyrimidine)
Ta utomeriza tion only ha ppe ns jus t be fore DNA polyme ra s e is a bout to read the
ba s e
- Sponta ne ous and/or induced le sions
Les ions ca n be introduce d 3 ways:
- By repla cing a ba s e in DNA
- By alte ring a bas e so tha t it s pe cifically mis pa irs with a nother bas e
- By dama ging a ba se s o that it can no longe r pa ir with a ny ba s e under a ny
condition
Alte rna tive ways to dete ct S NP s
- One technique to s a ve on time and/or e xpe ns e is known a s Re s tric tio n Fra g m e n t
Len g th Po lymo rp h is m s (RFLP )
RFLP depends on the use of re striction e nzyme s , which a ct a s mole cula r
scis s ors . The y a re things like ba cteria l e nzyme s . The ir job is to cut DNA a t
spe cific DNA s eque nce s known as res triction sites
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