Genetic Principles Flashcards
Give examples of typical mendelian inheritance mechanisms
Autosomal dominant
Autosomal Recessive
X linked
What patterns would you be able to see on a pedigree for a genetic condition with autosomal dominant inheritance?
Vertical pattern of inheritance
Both males and females affected
Possible for it to be passed from father to son
By looking at the patterns on a pedigree, how can an autosomal dominant condition be differentiated from an x linked condition?
In AD it is possibe for the condition to be passed from father to son
Autosomal dominant conditions can have variable expressivity. What does this mean?
That within a family people may have the same genetic alteration buy can have the disease to different extents
Some autosomal dominant conditions exhibit complete penetrance. What does this mean?
That if the mutation is inherited then the individual will definitely develop the disease
Some autosomal dominant conditions exhibit incomplete penetrance. What does this mean?
That if if the mutation is inherited then the individual may not go on to develop the disease at all
Give an example of an autosomal condition which has complete penetrance?
Huntington’s disease
In addition to to the mutated genes of the autosomal dominant condition itself, what other genes can affect the severity and/or penetrance of the condition?
Modifier genes
Give examples of autosomal dominant conditions
Inherited breast or colon cancer
Polycystic kidney disease
Huntington’s disease
Neurofibromatosis type 1
What is meant by the term ‘compound heterozygote’?
The individual has two different mutations in the same gene resulting in the disease
What is meant by the term ‘double heterozygote’?
The same fault or mutation is present in more than one gene within an individual
In autosomal recessive inheritance, if you see an affected child then you should assume that the parents are carriers. T/F?
True
What is the term for an individual who has inherited only one faulty copy of a gene for an autosomal recessive condition?
Carrier
What is meant by the term ‘consanguinity’?
The parents are related e.g. the parents are cousins
Give examples of autosomal recessive conditions.
Cystic fibrosis
Phenylketonuria
Spinal muscular atrophy
Congenital adrenal hyperplasia
There is often variable expressivity of autosomal dominant conditions. Is this also true for autosomal recessive conditions?
No - expressivity is more constant within a family for AR conditions
What type of inheritance mechanism exhibits a horizontal pedigree pattern?
Autosomal recessive
What patterns would you be able to see on a pedigree for a genetic condition with x linked recessive inheritance?
Knight’s move pattern
No male to male transmission
Mostly or only males are affected
Explain the mechanism of skewed X inactivation by which females can be mildly affected by X linked recessive conditions.
In the early embryo, within each cell, one of the X chromosomes in inactivated or switched off. Therefore, in female carriers of an X linked recessive condition, if in the majority of cells the damaged allele is randomly selected to remain switched on then the individual can be mildly affected by the disease
What is the term for females in a family who are mildly affected by X linked recessive conditions due to skewed x inactivation?
Manifesting carrier
Give an example of an X linked recessive condition
Duchenne’s muscular dystrophy
Give examples of X linked dominant conditions
Vitamin D resistant rickets
Incontentia Pigmentia
Rett syndrome
Incontentia pigmentia and rett syndrome are X linked dominant conditions which are lethal in males. T/F?
True
There is a vertical pattern of inheritance for X linked dominant conditions. T/F?
True
If a male with an X linked recessive condition has a daughter, then this daughter will be affected by the disease. T/F?
False - this would be true of an X linked dominant condition but in an x linked recessive condition the daughter of an affected male would be an obligate carrier
More men than women in a family are likely to be affected by an x-linked dominant condition. T/F?
False - there is usually a 2:1 ratio of women:men affected by an x-linked dominant condition in a family
What term describes the increasing severity and earlier age of onset in successive generations exhibited in some genetic conditions?
Genetic anticipation
Give examples of conditions which exhibit genetic anticipation.
Huntington’s disease
Fragile x syndrome
Myotonic dystrophy
Which genetic condition is caused by a CAG repeat which expands in subsequent generations?
Huntington’s disease
What is pseudo-dominant inheritance?
A type of autosomal recessive inheritance where, because of the condition’s high carrier frequency or because o consanguinity, it appears as autosomal dominant inheritance
Give an example of a pseudo-dominant condition?
Gilbert’s syndrome
How does mitochondrial DNA differ from nuclear DNA?
Mitochondrial genome is much smaller
Circular DNA
No introns
Mitochondrial DNA is only inherited from which parent?
The mother
Mutations affected the mitochondria DNA of the mother have what percentage chance of being passed on to the children?
100%
Mutations affected the mitochondria DNA of the father have what percentage chance of being passed on to the children?
0%
Since mutations affecting the mitochondria DNA of the mother have a 100% chance of being passed on to the children, will all the children be affected by the disease?
Not necessarily since the severity of the resulting condition is variable
What tissues do mitochondrial genetic conditions typically affect?
Brain
Muscles
Eyes
What is meant by the term ‘heteroplasmy’ and what gives rise to this?
The presence of more than one type of organellar genome because of the fact that not every mitochondria within a cell might be affected by a mutation
