Genetics and Biometrics

1
Genetics and Biometrics
2
Genetic 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.

3
Genetic Definitions (Contd)

• 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

4
Genetic Definitions (Contd)

• 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

5
The Differences

• Between individuals of the same sex
• lt0.5
• Between humans and chimpanzes
• lt2

6
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)

7
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

8
Detection of Genomic RFLP

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

9
Detection of RFLP by PCR
10
Length Polymorphisms

• Minisatellites and Microsatellites
• Sequences repeated in tandem
• Highly variable number of repetitions between
  individuals thus several alleles
• Length polymorphisms
• Molecular phenotypeGenotype  
• Minisatellites
• Low distribution throughout the genome Mostly
  found within telomeres
• Microsatellites
• High distribution throughout the genome
• VNTR

11
VNTRs

• The number of repetitions
• different lengths
• different alleles
• different genotypes
• different molecular phénotypes

12
Length Polymorphisms of Microsatellites

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

13
VNTR (Contd)

• Highly variable number of repetitions individuals
• Thus several alleles within a population
• Ex.

Different fragment lengths would be generated by
a digestion at the indicated positions
14
Detection of VNTR by PCR
15
Biometrics
16
VNTR Profile of Nuclear Genome
From whom does the blood come from?
17
VNTR Profile of Nuclear Genome
Who is Bobs father?