Genetics and Biometrics

DefinitionsDefinitions

LocusLocus The position of a coding or non coding The position of a coding or non coding

genetic element genetic element GeneGene

All the nucleotide elements required for All the nucleotide elements required for the expression of a transcriptthe expression of a transcript

Promoter, ORF, introns, exons, etc.Promoter, ORF, introns, exons, etc.

Genetic Definitions Genetic Definitions (Cont’d)(Cont’d)

AlleleAllele Version of a genetic element at a given Version of a genetic element at a given

locuslocus Everyone necessarily has two alleles for each Everyone necessarily has two alleles for each

genomic locusgenomic locus– The two alleles may be the sameThe two alleles may be the same

HomozygotesHomozygotes– The two alleles may be differentThe two alleles may be different

HeterozygoteHeterozygote A population of individuals may have multiple A population of individuals may have multiple

alleles of a genomic locusalleles of a genomic locus

Genetic Definitions Genetic Definitions (Cont’d)(Cont’d)

Genotype:Genotype: Nucleic acid sequence responsable for the Nucleic acid sequence responsable for the

phenotypephenotype Physical detection by molecular techniquesPhysical detection by molecular techniques

Phenotype:Phenotype: Trait that can be distinguished resulting Trait that can be distinguished resulting

from a genotypefrom a genotype Several different genotypes may have the Several different genotypes may have the

same phenotypesame phenotype

The DifferencesThe Differences

Between individuals of the same Between individuals of the same sexsex <0.5%<0.5%

Between humans and chimpanzesBetween humans and chimpanzes <2%<2%

Molecular MarkersMolecular Markers

Characteristics of the nucleotide Characteristics of the nucleotide sequencesequence

The phenotype often corressponds The phenotype often corressponds to a specific genotypeto a specific genotype Restriction polymorphisms (RFLP)Restriction polymorphisms (RFLP) Length polymorphisms (VNTR)Length polymorphisms (VNTR)

Variable number of tandem repeatsVariable number of tandem repeats Single nucleotide polymorphisms (SNP)Single nucleotide polymorphisms (SNP)

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Length Polymorphisms - RFLPLength Polymorphisms - RFLP

Based on the presence or absence of Based on the presence or absence of a restriction site at a given poistiona restriction site at a given poistion Ex. The enzyme EcoR1 recognizes and Ex. The enzyme EcoR1 recognizes and

cleaves the sequence:cleaves the sequence: GAATTCGAATTC A single base mutation abolishes the siteA single base mutation abolishes the site GAGAGGTTCTTC

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Detection of Genomic RFLPDetection of Genomic RFLP

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11 22

Genome 1 Genome 2

Polymorphism

2 possible phenotypes– 2 alleles can be distinguished– Several possible genotypes

A BE E E A+B*E E

Detection of RFLP by PCRDetection of RFLP by PCR

Length PolymorphismsLength Polymorphisms

Minisatellites and Microsatellites: Minisatellites and Microsatellites: Sequences repeated in tandemSequences repeated in tandem

Highly variable number of repetitions between individuals; Highly variable number of repetitions between individuals; thus several allelesthus several alleles

Length polymorphismsLength polymorphisms Molecular phenotype=Genotype  Molecular phenotype=Genotype  

MinisatellitesMinisatellites Low distribution throughout the genome Mostly Low distribution throughout the genome Mostly

found within telomeresfound within telomeres Microsatellites:Microsatellites:

High distribution throughout the genomeHigh distribution throughout the genome VNTRVNTR

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VNTRsVNTRs

The number of repetitionsThe number of repetitions = different lengths = different lengths = different alleles= different alleles = different genotypes= different genotypes = different molecular phénotypes= different molecular phénotypes

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Length Polymorphisms - VNTRLength Polymorphisms - VNTR

DNA Region where tandem copies DNA Region where tandem copies of di-, tri- or tetra repeated units of di-, tri- or tetra repeated units are locatedare located

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Exemples:

Dinucleotide repeat GTGTGTGTGTGT……

Trinucléotide repeat ACGACGACGACG……

Tetranucléotide repeat TATCTATCTATC……

VNTR VNTR (Cont’d)(Cont’d)

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Highly variable number of repetitions Highly variable number of repetitions individualsindividuals Thus several alleles within a populationThus several alleles within a population

Different fragment lengths would be generated by a digestion at the indicated positions

CA CA CA CA CA

CA CA CA CA CA CA CA CA

CA CA CA CA CA CA CA CA CA CA CA CA

Allele 1

Allele 2

Allele 3

Detection of VNTR by PCRDetection of VNTR by PCR

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AGCGGCTTAATGCTGCTGCATAACATTGCIndividual 2

AGCTGCTTAATGCTGCTGCTGCTGCTGCTGCATAACATTGC

Individual 1

Amplification & gelseparation

1 2

Biometrics

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VNTR Profile of Nuclear VNTR Profile of Nuclear GenomeGenome

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From whom does the blood come from?

VNTR Profile of Nuclear VNTR Profile of Nuclear GenomeGenome

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Who is Bob’s father?

Bob Luc Paul TomMarc