Genetic 2.3: Non-Mendelian Genetics Flashcards
Hérédité mitochondriale properties
Hérédité « cytoplasmique » (≠ nucléaire!!; dna is in the mitochondria)
Transmission is always MATERNAL
the fathers mitochondria in the sperm is degraded before it makes it
ALL OF THE KIDS WILL HAVE IT!!!! However, Variabilité de l’atteinte selon le nombre de mitochondries ayant la mutation
Not all mitochondria will have the mutation and not all divided cells will have the mutation
Because division of mitochondria is not very well regulation: 2 cellules filles peuvent recevoir des proportions de mitochondries « atteintes » très différentes
What kind of transmission is this and why?
https://photos.google.com/album/AF1QipNG9KUYAJ5KLGtK-7glOYzqmmKc4TZiqBbw
This is Transmission mitochondriale
You can see that the affected fathers never give to their offsprings and that all afftcted mothers will give to children
Could a child of a annormal mitochondrial DNA mother not be affected?
All the children will have damaged mitochondria but in a HETEROPLASMIE way!!!!
SO whether they have a phenotype will depend on how many damaged mitochondria they inhereted from the mother-> HETEROPLASMIE
Variabilty in how many you receive. There is a mitochondrial threshold -> certain seuil
Conditions avec hérédité mitochondriale-> Affectent tous les tissus puisque la production d’énergie des cellules est affecte. Mais touchent plus souvent!!
tissu nerveux, musculaire, hépatique
Variabilité dans les niveaux d’atteinte, l’âge à la présentation, types de symptômes
you might not have that many mutated mitos as a child but they continue to multiply and it can hit as an adult
Myoclonic Epilepsy with Ragged Red Fibers-MERRF
What kind of disease?
Exemple d’hérédité mitochondriale that has a vast variability in expression based on where it is expressed and how many mitochodria are affected
All sorts of disease based on chance:
Épilepsie myoclonique
Myopathie (parfois cardiomyopathie)
Ataxie
Démence
Surdité
Atteinte rénale et diabète possible
Define Mutations dynamiques
Conditions causées par une expansion de triplets de nucléotide instables
lors de la méiose
Gène normal: Segment d’ADN contenant des séquences répétées un
certain nombre de fois (ex: triplet CGG)
- Nombre de répétitions peut s’allonger de génération en génération -> A partir d’un certain seuil, le risque d’une expansion du nombre de triplets augmente
A partir d’un certain seuil -> maladie
Often this mutation oc
Example: 8 CGG is normal but 80 CGG is not normal. Often this mutation occurs in meosis
What is concept de anticipation?
anticipation = increase of disease severity with every generation
A partir de la prémutation, le nombre de répétition augmente d’une génération à l’autre et est
associé à une sévérité plus grande ou un âge d’apparition plus précoce proportionnel à la taille
de l’expansion (nombre de répétitions) = l’anticipation
What is premutaion?
Concept related to Mutations dynamiques
IT is when the next generation will show a phenotype due to the increased number of triplets in the current gen
What is Slipped mispairing?
Concept related to Mutations dynamiques
Due to the many copies of triplets it is harder for the polymerases to find exactly where they left off. As such they might add a few more due to the loops that can form.
Dystrophie myotonique (Steinert) type of disease
Maladie autosomique dominante related to Mutations dynamiques
Syndrome du X Fragile type of disease and what is special
Forme monogénique la plus fréquente de déficience intellectuelle
More frequent in guys (due to X innactivation)
premutation does not give X Fragile but another disease called FXTAS -> ’ataxie/tremblement
Syndrome de Huntington, type and what is special?
Maladie of dynamic mutations Expansion de triplets CAG
Transmission autosomique dominante
Problem:
Maladie neurologique à début adulte en moyenne autour de 40taine
because phenotype shows this late, likely that the person already has had their kids
Dégénératif. Décès environ 15-18 ans après le diagnostic
Explain the problem with trisomy or monosomy rescue related to parental imprinting. Explain how it happens and the issue.
**Parental Imprinting: ** This is a process where a gene from one parent is methylated and thus inhibited. Example, the 15th chromosome from each parent is not identical due to this methylation.
**Trisomy Rescue: ** In an event of an improper split during meiosis, a cell may end up with three copies of chromosome 15. The cell can adapt to maintain the correct chromosome count during division. Example, the cell might eliminate one of the father’s chromosomes, resulting in the offspring having two maternal copies of the chromosome. This leads to Prader-Willi, maternal rescue
Monosomy Rescue: This occurs when a parent fails to contribute a chromosome, prompting the cell to duplicate its own chromosome to compensate. The result is two copies of the chromosome from the same parent, which is a simpler scenario compared to trisomy rescue. However, this leads to the inhibition of certain regions on the duplicated chromosome. This leads to **Angelman Syngrome. Paternal rescue
**
**Uniparental Disomy: ** This condition arises when an offspring inherits two copies of a chromosome from a single parent. Consequently, genes that are typically unmethylated on the father’s chromosome become methylated on the mother’s chromosome, which can lead to disease due to lack of genes.
What is Empreinte parentale?
The concept that for certain specific genes, we express specifically that found on the paternal or maternal chromosome while silencing the other and vice versa. Methylation of the inhibited gene region on one of the chromosomes
Certaines régions du génome diploïde ne sont exprimées qu’à partir de l’allèle paternel ou maternel
L’allèle non exprimé a une empreinte qui l’empêche d’être exprimé en tout temps (méthylation de la région promotrice)
What is Syndrome de Prader-Willi
and what are 3 things that could cause it?
Syndrome de Prader-Willi is a disease of missing the gene for SNRPN.
Gène SNRPN is usually on the paternal copy of the chromosome as the mother one is methylated.
3 Things that can lead to this:
délétion/mutation of paternel allele
anormal methylation of the father’s allele
: disomie maternelle
