C2 - Genetic expression Flashcards
How are inheritance patterns analyzed?
Using genetic and familial pedigree diagrams.
What factors contribute to variation in populations
some variation is due to genetics, some is environmental, and some is down to both.
What do pedigrees show
The presence or absence of genetic traits in family lines.
How many genetic disorders are known to occur in humans?
Several thousand.
Name two common genetic disorders
Cystic fibrosis and sickle cell anemia
What can cause genetic disorders?
Single gene defects or chromosome abnormalities.
What are the inheritance patterns of gene defects?
Dominant or recessive patterns.
What is the incidence of CF in the UK?
1 in 1600 people born.
What is the carrier frequency of CF in the UK
1 in 20 people are symptomless carriers.
What does the CFTR gene code for
Chloride ion channel protein in cell surface membranes.
which tissues is the CFTR protein located
Lungs, gut, and reproductive tracts.
What mutation causes 70% of CF cases
Deletion of a codon leading to loss of phenylalanine at position 508 in the CFTR protein
What is the effect of the mutation on the CFTR protein?
Impairs the function of the ion channel.
What is the genetic makeup of symptomless carriers?
One mutated allele and one normal allele of the CFTR gene.
what age do symptoms of Huntington’s disease usually appear?
After the age of 35 years.
What gene mutation is responsible for Huntington’s disease?
Mutation in the HTT gene.
What is the function of the HTT gene
Codes for the huntingtin protein important for normal brain neuron function.
What are the early symptoms of Huntington’s disease
Low mood, poor coordination, and involuntary twitching movements (chorea).
How does Huntington’s disease progress?
Involuntary movements worsen, along with difficulties in walking, swallowing, talking, personality changes, and dementia
What is the risk of inheriting Huntington’s disease
individuals with 27-35 CAG repeats do not develop the disease but are at risk of having children with the disease due to expansion of the repeat sequence during meiosis.
People who have 36–40 or more CAG repeats may develop the disease later in life.
What type of mutation is within the HTT gene when Huntington’s disease is present
The mutation is an expanding triple nucleotide repeat and is sometimes called a ‘stutter’
What is the chance of a child inheriting Huntington’s disease when one parent is affected?
50% (1 in 2) at each pregnancy
What is the inheritance pattern of Huntington’s disease?
Autosomal dominant-only one mutated allele needs to be inherited for the disease to develop.
Dominant Allele
Dominant alleles will show their affect even if the individual only has one copy of this
allele
Recessive Allele
Recessive alleles will only show their effect if the individual inherits two copies of the
allele, one from the mother and one from the father
Genotype
The set of genes in DNA responsible for a particular trait
Phenotype
The physical expression of those genes, e.g., eye colour
Heterozygous
Possessing two different alleles for a particular gene (e.g.,one dominant and one recessive)
Homozygous
Possessing the same alleles for a particular gene (e.g., two recessive)
Allele
Different versions of the same gene
What do the XY chromosomes determine in humans
Our sex.
females have XX
males have XY
How many genes are on the human X chromosome
Over 1000 genes.
What happens if a female has one abnormal allele on one X chromosome
She will likely have a functioning allele of the same gene on her other X chromosome
What happens if a male has one abnormal allele on one X chromosome
He will likely to be affected by the condition as he doesn’t have another copy of X chromosome
Which gene on the X chromosome is involved in Haemophilia A
The gene that codes for factor 8, a blood clotting protein.
What happens if the allele for factor 8 is faulty
It produces a non-functioning factor 8, leading to impaired blood clotting
If a female passes the faulty allele for factor 8 to her son, what will he suffer from
Haemophilia A, as he lacks a functioning allele on his Y chromosome.
Why may internal hemorrhage in Haemophilia A not be immediately apparent
injuries without external wounds may not show immediate symptoms, unlike injuries with visible cuts.
What does aneuploidy refer to
A condition where the number of chromosomes in the cells is abnormal.
How does aneuploidy occur?
Failure of homologous (same) chromosomes to separate during meiosis.
What happens if a gamete with an extra chromosome is fertilized?
The embryo will have three copies of a particular chromosome.
Which chromosome abnormality is associated with Down syndrome?
An extra copy of chromosome 21.
Is Down syndrome inherited from parents
No, it arises spontaneously and is not inherited.
Are there symptomless carriers for Down syndrome?
No, individuals with an extra chromosome 21 will have Down syndrome.
What do proto-oncogenes regulate
Cell division, growth, and differentiation.
What happens when mutations occur in proto-oncogenes?
They become oncogenes, causing uncontrolled cell division
What is the role of the p53 gene
Regulating cell division and preventing uncontrolled cell growth
What can happen if there is a mutation in the p53 gene
Uncontrolled cell division, tumor formation, and potential development of cancer.
How do benign and malignant tumors differ?
Benign tumors are non-cancerous, grow slower, do not metastasize, and have more normal features, while malignant tumors are cancerous, grow rapidly, and can spread to other parts of the body
Why is it necessary to obtain DNA samples
Reasons include serious crimes, paternity tests, and genetic disease screening.
What is a common technique used for obtaining DNA samples
Swabbing with buccal (cheek) swabs.
How is a buccal swab collected
The inside of the inner cheek is scraped with a moist swab for up to 1 minute, then allowed to dry and placed in a sterile container
Importance of avoiding certain activities before buccal swab collection
is it important to avoid eating, drinking, smoking, before a buccal swab To prevent potential contamination and ensure better results.
What are some limitations of buccal swab collection
Over-saturation of swabs, insufficient scraping, and difficulty in determining if enough cells are collected.
How is a blood sample collected
A needle is inserted into a vein to draw blood, which is collected in sterile medical tubes.
What is an advantage of blood sample collection over buccal swabs
The sample is visible.
What are some limitations of blood sample collection
Pain for some individuals, discomfort for children, difficulty with small veins, and the need for a trained medical specialist.
Reliability of DNA test results from both methods
Yes, both methods provide highly reliable DNA test results
What tests are offered to pregnant women to test for genetic and chromosomal conditions?
Antenatal tests
What is the name of the test carried out between the 11th and 14th weeks of pregnancy?
Chronic Villus Sampling (CVS).
Methods of CVS
two methods used for Chronic Villus Sampling (CVS)? - Transabdominal CVS and Transcervical CVS.
How is Transabdominal CVS performed
A needle is inserted through the abdomen into the uterus and placenta guided by ultrasound scanning
How is Transcervical CVS performed
A small tube or forceps are inserted through the vagina and cervix to reach the placenta guided by ultrasound scanning.
What can be done with the cells collected through CVS
The number of chromosomes can be counted and the chromosome structure can be checked.
What are some limitations of Chronic Villus Sampling (CVS)?
It cannot test for every condition, and sometimes results can be inconclusive due to insufficient cell collection.
What is the name of the test carried out between the 15th and 20th weeks of pregnancy?
Amniocentesis.
How is amniocentesis performed
- A long, thin needle is inserted through the abdomen wall using an ultrasound image to guide it, and a small sample of amniotic fluid is collected.
Implications of positive test results in amniocentesis
Implications will be discussed in counseling sessions, and couples will have to decide the next steps
