Genetics COPY from Principles Collated Flashcards
2 factors of a disease?
Environment + genes
What processes occur in a 5’ -3’ direction?
Replication and reading of DNA structure
What is the DNA backbone composed of?
Sugar-phosphate
4 bases in DNA?
Thymine
Adenine
Cytosine
Guanine
What happens when DNA strand associates with proteins (name example of type of proteins)?
Histones
It is wound into a chromosome structure
Explain what can happen to DNA in replication and what it’s defect can result in?
Damaged during replication
-Repair mechanisms exist but when these have defects disease occurs
The stages of cell cycle?
G1, S, G2, M, G1
What stage of cell cycle does DNA synthesis take place in?
S phase
What unzips DNA molecule?
DNA Helicase
Which enzyme copies the 5’-3’ strand?
DNA polymerase
Interphase?
Cell is not dividing the stages of cell cycle included in this is S, G0, G1 & G2
Cell grows and is metabolically active
G2?
After DNA replication the cell continues to grow and produce proteins
M phase?
Mitosis checkpoint
Are chromosomes aligned on the spindle
G1?
Cell may increase in size, produce RNA and synthesize protein
S phase?
Period of DNA replication
Going from 2n- 4n in preparation for mitosis
How does DNA polymerase work with Okazaki fragments?
Copies the 3’-5’ strand which DNA ligase joins
Mitosis outcome?
One diploid cell becomes two identical daughter diploid cells
Meiosis outcome?
One diploid parent cell becomes 4 haploid daughter cells
-crossing over occurs to produce variation
-Gamete formation
Describe an RNA strand?
-Single stranded
-Ribose sugar
-Uracil replaces thymine
Brief description of DNA-> protein?
DNA
| Transcribing and splicing
RNA
| Translation
Protein
In detail transcription and translation?
-DNA transcribed to pre-mRNA
-Pre-mRNA pliced (removal of introns) to form mRNA
-mRNA translated to protein (3 bases= 1 amino acid/stop codon)
-Protein is modified and moved around cell
Types of sequence variations within a gene?
Changes in promoter sequence
Changes in exon sequence
Types of sequence changes in DNA between genes?
SNP’s
Larger deletions/duplications
What is a polymorphism?
Any variation in the human genome which has a population frequency of >1%
Genetic variation that is prevalent in the population but is not in itself disease causing
it can be exist as SNP or CNV
A polymorphism will cause disease. True or false?
FALSE
It can cause a disease but not in it’s own right, may predispose to a common disease
it identify as Definitely benign (harmless)
What is a mutation?
Gene changes that cause a genetic disorder
-any heritable change in the human genome
How many mutations required in a classical genetic disease?
One mutation sufficient to cause disease
Describe multifactorial disease and it’s relation to polymorphisms?
Multiple polymorphisms cause a risk of disease
Chromosome make up of a normal female?
46XX
What consists of an unbalanced chromosome rearrangement?
-Extra or missing chromosomal material
-Usually 1 or 3 copies of some of the genome
-Concerning for development
Aneuploidy?
Whole extra or missing chromosome
Down Syndrome is probably the most well-known example
Translocation?
Rearrangement of chromosomes
Describe genome defect of Down syndrome in a boy?
Trisomy 21
47XY + 21
What would happen if a genome was 47XY + 14? and what is the formula to describe this?
MIscarraige
Trisomy (three copies of one chromosome) 14
What is the genome for Edward’s syndrome?
Trisomy 18
47 XY + 18
Which genetic condition is 45X?
Turner’s syndrome
What is 47 XXY?
Klinefelter syndrome
is where boys and men are born with an extra X chromosom
What is translocation?
2 acrocentric chromosomes stuck end to end
Most common ones are 13 &14, 14&21 and 14&15
What does robertsonian translocation increase the risk of?
Trisomy in pregnancy (Down’s or miscarraige)
mothers with robertsonian translocations associate with chromosome 21 are at high risk of having offspring down syndrome
Acrocentric?
A chromosome in which the centromere is very close to p end.
in other words
Chromosome with short p arms and long q arms
What is a first line chromosome test?
Microarray CGH
What does a microarray CGH detect?
Any missing or duplicated piece of chromosome, finds polymorphisms.
It detects size of imbalances chromosome rearrangements NOT BALANCED
It has higher resolution
Gonadal mosaicism other term for it and explanation?
Germline mosaicism
-mutation present in the eggs or sperm and not somatic cells thus increase risk of autosomal dominant conditions even if parent unaffected
Somatic mosaicism?
New genetic variations occurs during every somatic cell division and parents can be unaffected or affected
All cells suffer mutations as they divide
-Repair mechanisms exist for this.
Somatic mosaicism is a postzygotic
mutation that occurs in the soma, and it may occur at any developmental stage or in adult tissues.
What is mosaicism?
the presence of two or more cell lineages with different genotypes arising from a single zygote in a single individual
How genes are analysed and how mutations are detected?
PCR
Sequencing
Filtering
Types of mutation?
Missense
Premature stop
In frame
Out of frame
Splicing or promoters mutation
Mutations that inactivate or activate a gene
Missense?
alteration in DNA that result in different amino acid being incorporated into the structure of the protein
eg Instead of
The cat sat on the mat
it would be
The caR sat on the mat
Premature stop?
Base change causing this **
What causes an in frame or out of frame mutation?
Insertion or deletion of base
What do we use to analyse deletions and duplications?
aCGH - for balanced rearrangements
PCR is used for analysing?
For changes in small number of BP
How does PCR work?
Allows us to select one small piece of human genome from a patient (100-10000 bases) and amplify it to make lots of copies
Example of an insertion mutation in the sentence the cat sat on the mat?
The cat sPa to nth ema t
Example of deletion out of frame and then in frame fro the cat sat on the mat?
Out= The cas ato nt hem at
In= The cat on the mat
What are tumour suppresors?
Genes that stop cells dividing if switched on
Oncogenes?
Genes that start cells dividing when switched on
Penetrance?
Penetrance of a mutation is the likelihood that the mutation will cause a disease phenotype in an individual.
The likelihood of having a disease if you have a genetic mutation
Expression?
Variation in disease severity if you have a mutation
Promoter and splice site sequence changes?
Stop transcription or cause abnormal splicing
What effect does a base change causing amino acid change have?
Change in protein sequence. May or may not reduce protein function
What are mendelian disorders?
A disease that is caused by a change in a single gene
Describe characteristic of an autosomal dominant disorder?
only one copy is needed to cause the disease, therefore it is easily passed on through the generations
- Offspring have a 50% chance of inheriting the disease
Describe characteristics of an autosomal recessive disease?
two copies are required to get the disease
- Their offspring has a 25% of inheriting a disease (50% will be carriers)
Fancy term for incestuous?
Consanguineous
Describe characteristics of an X-linked recessive disease?
the fault is on the X chromosome. Since males only have one, they show signs of the disease.
Females are carriers and will not show major features of the disease
If a female is a carrier:
- Half of her male children will be affected (i.e. 1 out of 2 in the diagram above)
- Half of her female children will be carriers
If a male is affected:
- All of his male children will be unaffected (NO MALE-TO-MALE TRANSMISSION) 🡪 males only pass on an Y to their male children!
- All of his female children will be carriers
If a mother is a carrier of an x-linked recessive disease what is the chance her son or daughter is affected?
50% chance of daughter carrier
50% chance male is affected
Describe characteristics of Mitochondrial disease?
Inherited almost exclusively maternally
-point mutations and deletions occur
If mother effected all childern affected
if father effected no childern effected
Symptoms of mitochondrial inherited disease?
-Myopathy
-Diabetes
-Deafness
-Optic atrophy
-Stroke like episodes
-Encephalitis
Which disease is autosomal dominant?
Huntington’s disease
Non-mendelian inheritence?
Methylation/imprinting
Mitochondrial inheritance
Mosaicism
Which inheritance is common in incestuous families?
Autosomal recessive
Why would a female carrier show mild features of an X-linked disease?
X-inactivation
in female cells only one X chromosome is active
What is a CNV?
Copy number variation
They are extra or missing stretches of DNA
How mendelian inheritence works with factors like environment?
High penetrance
Small environmental contribution
Factors involved in multifactorial disease?
Genetic change is just another risk factor
penetrance for an one mutation is low
Individual genetic factors are treated the same as environmental risk factors
What happens in DNA methylation?
Leads to modification of histones which represses transcription.
this cause genes to be silence in cancer
What is imprinting?
The differences in gene expression depending on whether a gene is maternally or paternally inherited
What is angelman syndrome?
Neuro-genetic disorder caused by imprinting on chromosome 15
Symptoms of angelman disorder?
Developmental delay
Intellectual disability
Ataxia
Epilepsy
Happy demeanour
Frequent laughing and smiling
Heteroplasmy?
Different daughter cells contain different proportions of mutant mitochondria
-severity of phenotype depends on proportion and level of mitochondria/type of mutation
Characteristics gained by cells on progression to cancer?
Proliferation
Evasion of immune response
Acquire a vascular supply
Avoid apoptosis
Metastasis
Genes involved in cancer?
Oncogenes
Tumour suppressors
DNA repair genes
Drug metabolism
What are drug metabolism cells?
Genes that metabolise carcinogens
Mechanisms of gene activation? 3
Duplication of the gene
Activation of the gene promoter
Change into amino acid sequence
What does FISH stand for?
Fluorescence in situ hybrid
What can FISH do?
Light up specific bits of chromosome
What type of mutation causes a small proportion of familial breast cancer?
BRCA 1
What is BRCA 1 gene involved in ?
DNA strand repair
What is multifactorial predisposition?
Everyone is at some risk
Anyone with family history is at increased risk.
Common disease
identify the process in the diagram below
Reciprocal translocation
- Two broken off chromosome pieces of non-homologous chromosomes are exchanged
What is an example of a consequence of unbalanced reciprocal translocation
miscarriage
why is array CGH is first line chromsome test
- its cheap
- for unbalance give you quick results
what is a nonsense mutation ? and what its will result in ?
it happen in the DNA when a sequence changes gives rise to a stop codon rather than a codon specifying an amino acid.
This will lead to change in length of protein due to premature stop of translocation.
In G1 of Meiosis 1 what is the ploidy cells
2n (2diploid chromosomes)
sequence of events for protein synthesis?
Pre-mRNA, splicing, mRNA, translation and post translational modifications
the ways through which variation in genome can arise during meiosis
A. Independent assortment
B. Formation of chiasmata
C. DNA replication
D. Non-disjunction
Array comparative genomic hybridization used to detect
for unbalanced rearrangements. its array CGH
Central Dogma
a theory stating that genetic information flows only in one direction, from DNA, to RNA, to protein, or RNA directly to protein.
Redundancy
is where different codons can
encode the same amino acid. So your RNA
sequence can change and cause no effect on
protein sequence of amino acids
Variable penetrance
describes the clinical situation
where a person can have a disease causing
mutation but not show signs of disease.
High penetrance its a rare disease
low penetrance its common disease
what is the advantage and disadvantages of whole gene sequencing than sanger sequence
is much cheap than sanger sequencing However – it is more expensive than doing a singe gene traditionally, and will throw up lots of polymorphisms
only change in single amino acid is not evidence its related to specific disease. But if that change only present in the child and not the healthy parents and causes a disease than its strong evidence that it cause the disease. True /False
True
not only missense disease but also other mutations
and ITS Definitely pathogenic
When coming to have test for an untreatable
Which ethical principle is most important in genetic
counselling for your patient?
Patient autonomy
what is 47XXX ?
TrIple X syndrome
After transcription what is produced?
A
Pre-mRNA
How is mature mRNA obtained?
A
Splicing of introns to leave only exons which contain coding DNA
In terms of the cell cycle, which stage will the cell remain in most of its life?
A
G0
Which enzyme is responsible for unzipping DNA?
A
DNA helicase
How is variation obtained in meiosis?
A
Crossing over
Independent assortment
What is a polymorphism?
A
DNA variant which has a population frequency of greater than 1%
A polymorphism is a type of genetic variation that is common in human populations. One example is a single nucleotide polymorphism (SNP), which is a difference in a single nucleotide at a particular position in the DNA sequence. SNPs can be associated with differences in disease susceptibility or other traits among individuals.
What is a mutation?
A
A DNA variant which causes or predisposes to a specific disease?
How do polymorphisms and mutations differ?
A
Polymorphisms are functioning versions of genes
Mutations can be harmful
What is a missense mutation?
A
A wrong base is used in one of the codons
What is karyotyping?
A
It looks at chromosomes as a whole
Can see deletions of >5 million base pairings
What is a balanced translocation?
A
There is an even exchange of material between chromosomes
There is no missing or extra genetic information
Usually such chromosomes will still function
What is an unbalanced translocation?
A
There is an unequal exchange of genetic material between chromosomes
This results in extra or missing information
Usually these chromsomes do not function correctly
What are acrocentric chromosomes?
A
A chromosome in which the centromere is located very near the end of the chromosome
Two acrocentric chromosomes may stick together is very bad
What is fluorescent in-situ hybridisation?
A
FISH
Chromosomes can be labelled by fluorescent probes
This can aid in identifying aneuploidy (too many chromosomes in a cell) or translocations etc
What is the risk of a carrier mother passing on a sex-linked genetic condition to her son?
A
25%
What does the term penetrance mean?
A
The extent to which a particular gene is expressed in the phenotype of the individual carrying it
In females how is it decided which X chromosome undergoes X inactivation?
A
It is a random process
What is multifactorial disease?
A
Disease in which mutations in multiple genes combine with environmental factors to cause disease
Genes involved in multifactorial disease will have what level of penetrance?
A
Low
What do DNA methylation and acetylation affect about the DNA and histone binding?
A
They increase the strength of binding
This may slow the rate of transcription when excessive and may cause disease
Describe the meaning of imprinting
A
Differences in gene expression depending on whether a gene is maternally or paternally inherited
Mitochondrial DNA is inherited from where?
A
Almost entirely the mother
What is mosaicism?
A
The presence of two or more populations of cells with different genotypes in one individual
What are the two types of mosaicism?
A
Somatic - derived from a post-zygotic mutation
Gonadal - a person has two populations of cells in the gonads, one with a DNA mutation or chrmosome anomaly
BRCA1/2 mutations are associated with what?
A
Increased lifetime risk of breast or ovarian cancer
(BRCA1/2 are associated with DNA repair)
What is the normal function of the CFTR gene?
A
code for cystic fibrosis transmembrane conductance regulator (CFTR) which functions as a channel across the membrane that produces mucus, sweat, saliva, tears and digestive enzymes
It transports cholride ions out of the cell which indirectly controls the water movement allowing for thin free flowing mucus
Mutations in CFTR cause what?
A
Sodium is not pumped out the cell and into the lumen or digestive or respiratory passages so mucus is thick as water does not enter these areas
