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Genetics and Biometrics
Definitions
 Locus
 The
position of a coding or non coding genetic
element
 Gene
 All
the nucleotide elements required for the
expression of a transcript
 Promoter,
ORF, introns, exons, etc.
Genetic Definitions
(Cont’d)
 Allele
 Version
of a genetic element at a given locus
 Everyone
locus
necessarily has two alleles for each genomic
– The two alleles may be the same
 Homozygotes
– The two alleles may be different
 Heterozygote
A
population of individuals may have multiple alleles
of a genomic locus
Genetic Definitions
(Cont’d)
 Genotype:
 Nucleic
acid sequence responsable for the
phenotype
 Physical detection by molecular techniques
 Phenotype:
 Trait
that can be distinguished resulting from a
genotype
 Several different genotypes may have the same
phenotype
The Differences
 Between
individuals of the same sex
 <0.5%
 Between
 <2%
humans and chimpanzes
Molecular Markers
 Characteristics
of the nucleotide
sequence
 The phenotype often corressponds to a
specific genotype
 Restriction
polymorphisms (RFLP)
 Length polymorphisms (VNTR)
 Variable
 Single
number of tandem repeats
nucleotide polymorphisms (SNP)
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Length Polymorphisms - RFLP
 Based
on the presence or absence of a
restriction site at a given poistion
 Ex.
The enzyme EcoR1 recognizes and
cleaves the sequence:

GAATTC
 A single base mutation abolishes the site

GAGTTC
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Detection of Genomic RFLP
Polymorphism
E
A
E
B
E
E
1
Genome 1
*
A+B
E
2
Genome 2
2 possible phenotypes
– 2 alleles can be distinguished
– Several possible genotypes
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Detection of RFLP by PCR
Length Polymorphisms
 Minisatellites
and Microsatellites:
 Sequences repeated in tandem
 Highly variable number of repetitions between
individuals; thus several alleles
 Length polymorphisms
 Molecular phenotype=Genotype
 Minisatellites

Low distribution throughout the genome Mostly
found within telomeres
 Microsatellites:

High distribution throughout the genome

VNTR
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VNTRs
 The
=
=
=
=
number of repetitions
different lengths
different alleles
different genotypes
different molecular phénotypes
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Length Polymorphisms - VNTR
 DNA
Region where tandem copies of di-,
tri- or tetra repeated units are located
Examples:
Dinucleotide repeat
GTGTGTGTGTGT……
Trinucléotide repeat
ACGACGACGACG……
Tetranucléotide repeat
TATCTATCTATC……
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VNTR

(Cont’d)
Highly variable number of repetitions
individuals

Thus several alleles within a population
Allele 1
CA
CA
CA
CA
CA CA
Allele 2
CA
CA
CA
CA
CA
CA
CA
Allele 3
CA
CA
CA
CA
CA
CA
CA
CA
CA
CA
CA
CA
Different fragment lengths would be generated by a
digestion at the indicated positions
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Detection of VNTR by PCR
Individual 1
AGCTGCTTAATGCTGCTGCTGCTGCTGCTGCATAACATTGC
Individual 2
AGCGGCTTAATGCTGCTGCATAACATTGC
1
2
Amplification & gel
separation
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Biometrics
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VNTR Profile of Nuclear Genome
From whom does the
blood come from?
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VNTR Profile of Nuclear Genome
Bob
Marc
Luc
Paul
Tom
Who is Bob’s father?
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