2: Genetics and disease Flashcards
When a gene is transcribed, (exons / introns) are removed.
introns
What are introns?
Non-coding parts of a gene
What are exons?
Coding parts of a gene
Codons correspond to amino acids or ___.
stops
Approximately which percentage of the genome is exons?
2-3%
What do introns insulate genes from?
Promotors
What technique is used to analyse DNA at the genome level?
Array CGH
What techniques are used to analyse DNA at the level of individual base pairs?
PCR
Sanger Sequencing
Next Generation Sequencing (NGS)
What is a mutation?
A genetic variation which causes disease
What is a polymorphism?
A genetic variation which shows up in >1% of the population
not disease causing in and of itself
PCR allows a geneticist to ___ one small piece of genome many times.
copy / amplify
Codons with ___ base pairs will connect with one another.
complementary
What technique is used to analyse DNA after PCR?
Sequencing
What happens to the rate of transcription if there’s a promotor mutation?
No transcription or reduced transcription
What happens to the quantity of protein expressed by a gene with a promotor mutation?
No protein expressed or less protein expressed
A base change may introduce a new ___, cutting off the protein.
stop
If a base change alters the amino acid sequence, what may happen to the protein expressed?
Different protein
or no protein
How many base pairs does a missense mutation affect?
1
In a missense mutation, what happens to the codon associated with the changed base?
What happens to the amino acid associated with the codon?
Different codon
Different amino acid
What type of mutation involves a new base pair being shoved into a DNA sequence?
Insertion mutation
What are the two categories of deletion mutation?
In frame
Out of frame
Rather than Sanger sequencing, which tool is now available to sequence DNA?
Next generation sequencing (NGS)
Finding a disease-causing mutation in a genome is difficult due to the number of ___ which already exist.
polymorphisms
What is penetrance?
The likelihood of having a disease if you have a gene mutation
What does 100% penetrance indicate about a gene mutation?
It will always cause disease
What is a Mendelian Disorder?
How penetrant are these disorders?
A disease which is caused by a change in a single gene
High penetrance
What are the three categories of Mendelian inheritance?
Autosomal dominant
Autosomal recessive
X-linked
In autosomal dominant inheritance, how many copies of a faulty gene are required to cause disease?
Only 1 copy
How many generations tend to be affected by autosomal dominant diseases?
All of them
If one parent has an autosomal dominant gene for a disease, what are the chances of their child inheriting the disease?
50%
How many copies of a faulty gene do you need to inherit an autosomal recessive disease?
2 copies
How many generations tend to be affected by autosomal recessive diseases?
Only one
What risk do you have of inheriting an autosomal recessive disease if both of your parents are carriers?
25%
Which families have an increased risk of inheriting autosomal recessive diseases?
Families in which there is inbreeding (‘cosanguineous pairs’)
Relative to the X chromosome, how many genes does the Y chromosome carry?
Very few
Name a notable X-linked recessive disease.
Haemophilia A & B
Duchenne muscular dystrophy
In X-linked recessive disease, which chromosome carries the faulty gene?
X chromosome
In terms of X-linked recessive disease, what is a carrier?
A female who has the allele on one of her X chromosomes but not the other, so she doesn’t show major features of the disease
How many male children of a female carrier will inherit an X-linked recessive disease?
50%
How many female children of an affected male and female carrier with inherit an X-linked recessive disease?
50%
If a male affected by X-linked recessive disease has male children with an unaffected non-carrier, how many of them will be affected?
None of them
If a male affected with X-linked recessive disease has female children, how many of them will be carriers?
All of them
Why may a female carrier of X-linked recessive disease show mild symptoms of that disease?
Random X inactivation - some of her cells will express the mutated gene
Why does random X inactivation occur in females?
Prevents double dose of X-linked alleles (since the Y chromosome is inert)
Mendelian diseases tend to be related to (several small mutations / one high penetrance mutation).
one high penetrance mutation
What kind of polymorphisms are responsible for variation between people in a population?
Single Nucleotide Polymorphisms (SNPs)
What is a Copy Number Variation (CNV)?
Extra or missing stretch of DNA
How penetrant are mutations in multifactorial disease?
Low
Which lengthy studies can be done to figure out if a disease has a genetic component?
Recurrence risk in siblings
Twin studies
