Unit 1 Topic 2C Gene expression and Genetics Flashcards
Define mutations
permanent change in the base sequence of DNA
Process of mutation in protein
- The mutation caused a permanent change in the base sequence of DNA
- This caused the mRNA transcribed from the gene to change,
- Causing amino acid sequence transcribed by ribosomes to change
- The relative side chains of the amino acid are different, leading to different types and positons of bonding.
- Therefore there is a change in the shape of the protein produced.
a. This may cause… ie. a change in the active site of the enzyme produced.
What is a normal condition of someone without cystic fibrosis
- CFTR channel opens to let chloride ions out of the epithelial cells
- CFTR channel inhibits the opening of sodium channels, reducing the number of sodium ions that can get into the epithelial cells
- Water moves out of the cell by osmosis, as the solute concentration outside the cell is higher than inside the cell
- Mucus is kept runny and cilia beat to move mucus
What is the condition of someone with cystic fibrosis
- CFTR channel is absent/ doesn’t function properly. No chloride ions can be transported out of the epithelial cells
- No CFTR channels inhibit the opening and closing of sodium channels, so many sodium ions can get into the epithelial cells
- Water from mucus moves into the cell by osmosis, as the solute concentration inside the cell is lower than outside the cell
- Mucus thickens, the cilia are trapped in the thick and sticky mucus and cannot move effectively.
Process of Preimplantation Genetic Diagnosis
- Egg and sperm are fertilised outside of the body by in vitro fertilisation
- After a few rounds of cell division, a single cell is taken out of each embryo 3. The genetic makeup of the cell is tested
- Only embryos without faulty alleles are placed into the mother’s uterus to allow it to implant and grow.
Benefits of Preimplantation Genetic Diagnosis (PGD)
- Does not harm the embryo in any way
- Reduces the chance of having a baby with genetic disorder
- Avoids abortion as the discarding of the embryo is done before implantation into the uterus.
Process of aminocentesis
- Around 20mL of aminotic fluid is taken up using a needle and syringe through the wall of the abdomen
- During the 14-20th week of pregnancy
- Epithelial and blood cells are recovered from the amniotic fluid by centrifugation
- The cells are cultured for 2-3 weeks and then there is karyotyping DNA analysis to
- Determine the number of genetic defects
- Determine the sex of the baby
- Or test for the presence of (recessive allele)
Disadvantages of aminocentesis
- Carried out relatively late in pregnancy -> difficult to terminate pregnancy
- Long time for results to be available (2-3 weeks of cell culture)
- 0.5-1% chance of spontaneous miscarriage
Process of chorionic villus samplings (CVS)
- Some cells within the villi of the chorion are taken using a syringe via the cervix
- Between 8-12th week of pregnancy
- Tissue extracted can be tested immediately, karyotyping DNA analysis is done (i.e. process of pairing and ordering chromosomes of organisms
Disadvantages of chorionic villus sampling
- 0.5-1% of spontaneous miscarriage
- Problems in genes on paternal X chromosome cannot be detected: inactivated in fetal placental cells at the stage of pregnancy
Ethical concerns of genetic screening
Ethical issues:
- Consent: The unborn baby cannot give consent or make decisions about its future
- Abortion issue: belief that embryos are potential human beings from the start of conception, and that abortion would be impossible.
Social concerns of genetic screening
Social issues:
- False positive or false negative results could lead to couples making the wrong decisions, ie. a healthy baby would be aborted if there was a false positive result
- Designer babies: Screening embryos allows embryos to be selected on basis of factors other than health and people are concerned about the future of designer babies
Define gene
- A length of DNA on a chromosome
- that codes for the production of one or more polypeptide chains and functional RNA
Define genotype
The combination of alleles
Define phenotype
- The physical traits and observable characteristics of an organism
- Expressed as a result of the interactions of the genotype and the environment
Define allele
Different forms of a gene on the same gene locus
Define recessive allele
- different forms of gene on the same gene locus
- both allele need to be present to express its phenotype
- expressed only in homozygous condition or when the dominant allele is absent
Define heterozygous
- when an organism has two different versions of the same gene
Define homozygous
- when an organism has two copies of the same allele / both allele are the same
Define codominance
- Occurs when both alleles at a gene locus are fully expressed in the phenotype
- Two dominant alleles both contribute to the phenotype
- By showing a blend of both characteristics or characteristics appearing together
(e.g. blood type AB)
Define autosome
- chromosomes that are not X or Y chromosomes
Define sex chromosome
- a chromosome that determines the sex of an organism
Define monohybrid inheritance
Where one phenotypic characteristic is controlled by a single gene
Define polygenic inheritance
- More than one gene for a single characteristic or trait
- The genes are present on more than one locus
- The genes interact with each other
- When the genes interact with the environment, this results in more variation.
Define sex-linked characteristics
- A characteristic where the gene responsible for it is located on a sex chromosome.
- Traits carried on the X-chromosome in the non-homologous region : humans
Define disorder
A result of defective gene
Explain why doctors are more likely to screen individuals once they develop diabetes that use methods such as prenatal screening (3)
- because (prenatal testing) can cause abortion (1)
- because false negative or false positive results can be avoided (if patient already has diabetes) (1)
- because of issues arising if another genetic condition is found (1)
- because an individual could live a healthy life (as only a genetic predisposition) (1)
- because of the ethics associated with destroying embryos (IVF) (1)
Gene vs allele
Gene = sequence of amino acids
Allele = information coded by gene
(Provide examples if needed! Ref June 2021 Q4)
Genotype vs phenotype
Genotype = combination of alleles (e.g. TT/tt/Tt)
Phenotype = observable features
Explain why a mutation in the CFTR gene results in the production of very thick and sticky mucus (3)
- because the mutated gene results in a faulty (CFTR) protein (1) * so chloride ions do not move out of the cells (1)
- decreasing the water potential / solute potential inside the cell (1)
- therefore water {leaves the mucus / enters the cells} by osmosis (1)
(past paper: spec) The CFTR protein coded for by this mutation has one missing amino acid compared to the functioning protein. Explain how this mutation results in a non-functioning CFTR protein. (4)
- different sequence of the R group
- CFTR protein -> different tertiary structure
- different types of bonds between R groups
- movement of chloride ions through cell membrane is affected
(past paper: spec) Explain why people with cystic fibrosis may develop lung infections (4)
- produces very thick, sticky mucus
- due to reduced water transport from cells
- cilia lining airways are unable to move mucus
- microorganisms get trapped in the mucus
- mucus provides suitable growth conditions for growth of microorganisms
