Genetics :( Flashcards
Define congenital
Any abnormality present at birth, whether due to a genetic disease or not.
Define Consanguinity
Reproductive union between two blood relatives
What proteins does DNA wind around?
Nucleosomes (made up of approx 8 histones)
What are Robertsonian chromosomes?
Chromosomes that lack a p arm (pairs 13,14,15,21,22)
Describe a chromosome
p arm (short) and a q arm (long) joined by a centromere
What are the 3 human genomes?
Somatic, germline, mitochondrial
When are changes to the genome heritable?
When the changes are in the germline or mitochondrial genome.
What is a mutagen?
Exposure to a substance damages the DNA base sequence and causes a mutation. Can be in the womb or post-natal. E.g. radiation
What is a teratogen?
Exposure to a substance damages embryo or fetal development, can also be a mutagen if DNA is damaged. E.g. alcohol, viruses
What is a mendelian mutation?
A monogenic mutation, where a single mutation on a gene is causing disease.
What is a somatic mutation?
The mutation causing disease is found only in the affected tissue.
What is a de novo mutation?
The variant occurs first in the germ line/ zygote so is present in offspring but not parents’ somatic genome, so wasn’t heritable.
What is dosage sensitivity?
Many genes are dosage sensitive so that deletion or duplication of genetic material causes an imbalance and results in disease.
Define benign variant
Gene variant known to have no impact on health.
What are the two types of chromosome translocations?
Balanced (no gain or loss of material)
Unbalanced (loss or gain of material, results in genetic conditions)
What causes down syndrome?
Trisomy 21 - an extra copy of all or some of chromosome 21.
What causes Edwards syndrome?
Congenital condition caused by trisomy 18.
What is autosomal dominant inheritance?
Disease occurs in the heterozygous state (variant on only one gene). Tends to cause a gain of (toxic) function.
It has a 50% recurrence risk.
What does an autosomal dominant pedigree look like?
M/F affected in equal proportions
Multiple generations affected
Both genders can pass on to either gender of offspring.
Define penetrance
% of individuals with the variant that develop the medical condition.
Can be age related (used in preventative medicine)
some variants have higher than others
some individuals never develop the condition
Define variable expressivity
Same variant causing different symptoms /signs in different people.
Anticipation
The condition manifests in successive generations earlier or with more severe symptoms.
What is autosomal recessive inheritance?
Occurs in homozygous state, tends to cause loss of function
What does an autosomal recessive pedigree look like?
M/F affected in equal proportions
Affected individuals only in one generation
Parents could be related