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Genetics and Biometrics
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Genetic Definitions Locus Gene
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.
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Genetic Definitions (Cont’d)
Allele Version of a genetic element at a given locus Everyone necessarily has two alleles for each genomic locus 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
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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
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The Differences Between individuals of the same sex
<0.5% Between humans and chimpanzes <2%
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Molecular Markers Characteristics of the nucleotide sequence
The phenotype often corressponds to a specific genotype Restriction polymorphisms (RFLP) Length polymorphisms (VNTR) Variable number of tandem repeats Single 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 mutation of a single base abolishes the site GAGTTC
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Detection of Genomic RFLP
Polymorphism 1 2 A B E A+B * E Genome 1 Genome 2 2 possible phenotypes 2 alleles can be distinguished Several possible genotypes
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Detection of RFLP by PCR
A B E A+B * Amplification & Gel Separation Genome 1 Genome 2 1 2 1 2 After digestion Before digestion
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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 of Microsatellites
VNTR DNA Region where tandem copies of di-, tri- or tetra repeated units are located Examples: Dinucleotide repetitions GTGTGTGTGTGT…… Trinucléotide repetitions ACGACGACGACG…… Tetranucleotide repetitions TATCTATCTATC……
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VNTR (Cont’d) Highly variable number of repetitions individuals Ex.
Thus several alleles within a population Ex. CA Allele 1 Allele 2 Allele 3 Different fragment lengths would be generated by a digestion at the indicated positions
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Detection of VNTR by PCR
AGCTGCTTAATGCTGCTGCTGCTGCTGCTGCATAACATTGC Individual 1 AGCGGCTTAATGCTGCTGCATAACATTGC Individual 2 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 Luke Paul Tom Mark Who is Bob’s father?
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