Genetic diseases Flashcards
What is a genotype?
The genetic composition of an individual
What is a phenotype?
Appearance of an individual that results from the interaction between the environment and the genotype
What’s a karyotype?
Number and visual appearance of the chromosomes in the cell nuclei
What is meant by an autosomal dominant condition?
Affects autosomal chromosomes (1-22)
Dominant - manifests in heterozygous state
50% chance of child developing disorder is 1 parent is affected
What is meant by an autosomal recessive condition?
Affects autosomal chromosomes (1-22)
Recessive - manifests in homozygous state - two affected alleles
Incidence of carriers
What is a good way to recognise a condition is autosomal and not sex/linked?
Male to male transmission
NOT SURE IF THIS IS RIGHT
What’s an allele?
One or more alternatives of a gene at a given location (locus)
For example:
Gene: eye colour gene
Allele: Blue eye colour
In autosomal recessive and dominant conditions, are males and females affected equally?
Yarp
In what circumstances can autosomal recessive conditions be passed on? What’s the probability of having an affected child?
When both parents are carriers of a defective allele
1/4 chance child has disease
What is an X-linked condition?
A disease that occurs due to a defective allele of a gene carried on the X chromosome
How are males an females affected differently by X-linked diseases?
Males get the disease, as they only have one X chromosome, there isn’t another one to back it up!
Females are carriers of the disease as they have another X chromosome that is likely to be healthy
Give an example of a disease which is: A. dominant, A. recessive, X-linked
A. dominant - Huntington’s
A. recessive - Cystic Fibrosis
X-linked - Haemophilia
Look at some pedigrees!
Or else.
Explain Knudson’s 2 hit hypothesis.
A cell can only initiate a tumour when it contains 2 mutant alleles
A person who inherits a mutant allele must experience a second somatic mutation for a tumour to start developing
What is meant by lyonisation?
When one of the X chromosomes in each cell of a female is inactivated
Normal process that has to happen to prevent females having twice as many gene products as males
Remember the tortoiseshell cat! Mosaic
What is gonadal mosaicism?
When germ cells are a mixture of 2 or more genetically different cell lines
For example: half a man’s sperm cells are healthy and half have an abnormality
How does gonadal mosaicism affect offspring?
The father will be healthy as the mutation likely occurred after birth and only affects his sperm
Genetic abnormality can affect some or all of the children
What is meant by penetrance?
The percentage of people with the mutation that causes the disease that actually have a defective phenotype (show symptoms)
What is meant by variable expression?
Different people with the same genetic mutation showing a range of signs/symptoms - mild or severe form of the disease
What are multifactorial conditions?
Diseases that are due to a combo of genetic and environmental factors
Most of the common diseases are multifactorial
What is meant by the dominant negative effect?
A dominant allele that has a negative effect on the function the allele should perform
Or something along those lines!
What’s the difference between Mendelian and multifactorial inheritance?
Mendelian - diseases inherited by a single gene
Multifactorial - a result of interplay between genetic and environmental factors
