genetics

• Mandelian inheritance :

  1. Autosomal recessive
  2. Autosomal dominant
  3. X linked recessive
  4. X linked dominant (rare)
• Non mandelian inheritance :

  1. Mitochondrial
  2. epigenetic imprinting
• Mitochondria reproduce by simple fission .
• Hereditary factor exists in 2 copies called alleles .

  1 locus = 2 alleles
• 1 locus is needed for a phenotype to be expressed.
• Genetic mixing :

  1. Homologous recombination
  2. Fertilisation of sperm and oocyte
• Monogenic disease : a single gene mutation that causes a disease
• Monofactorial genetic disease : disease purely due to genes.

  1. monogenic
  2. polygenic
• Polygenic disease : mutations in several genes cause disease when combined together .
• Human haploid genome = 3.2x10*9 base pairs

  diploid = 6.4x10*9
• Mitochondrial DNA codes for 37 genes .

  • 24 RNA
  • 13 proteins in respiratory chain
• Epigenetic tags :

  • repressor and activator tags
  • transmitted in each cell division
  • reversible
  • 1st ex - X inactivation in females
  • 2nd ex - genomic imprinting
• Intergenic DNA includes 5' and 3' start and stop codons (untranslated elements) .

  Introns are non coding regions of RNA and DNA .
• Epigenetics : set of heritable changes that occur in DNA without modifying its sequence .
• DNA methylation leads to transcription being repressed .
• TAD : self interacting genome

  In heterochromatin -> repressed TAD compartments

  In euchromatin -> active TAD compartments
• Somatic cells : genomic imprint is conserved

  Primordial germ cell : genomic imprint supressed because zygote has both paternal and maternal chromosome that cannot be passed on like that .
• Transversion : purine replaces a pyrimidine or vice versa
• • Microsatellite DNA is a short DNA sequence that is repeated in a particular region of the genome.
  • These DNA sequences are usually non coding.
  • Used in forensic science .
• VNTR (variable number tandem repeat) is used in DNA fingerprinting .
• • SNV ( single nucleotide variant) is a substitution of a single nucleotide at a specific position in genome .
  • When present in at least 1% of population : SNP (single nucleotide polymorphism).
  • SNV are more stable than repeat sequences .
  • Easily identifiable through PCR or sequencing .
• 3 genotypes :

  • 2 homozygotes
  • 1 heterozygote
• De novo mutation :1/2 of gametes carry mutation

  Somatic mutation : none of gametes carry mutation
• NMD - nonsense mediated decay : elimination of mRNA containing premature stop codon
• Centromere : alpha satellite DNA
• telomere repeat sequence : TTAGGG
• 5 steps in prophase 1 :

  1. leptotene(baquet stage)- duplicated chromosome start to condense
  2. zygotene - chromosome pair by longitudinal pairing
  3. pachytene - crossing over
  4. diplotene - chromosomes separate except in chiasma
  5. diakinesis - separation complete