Topic 2C- Inheritance Flashcards
(8 cards)
Why does DNA replicate by semi conservative replication?
Describe what occurs in semi conservative replication.
To ensure that there is enough genetic material present within the organism so that cell division can occur successfully. Semi-conservative replication must occur during the synthesis phase of the cell cycle.
DNA helicase breaks the hydrogen bonds between the two antiparallel polynucleotide strands, leaving two separate polynucleotide strands. Free floating complementary base pairs line up against the strands, and DNA polymerase forms peptide bonds during condensation reactions, where hydrogen bonds will reform between the complementary base pairs. The DNA has now been semi conservatively replicated, forming one additional strand from the original strand.
This is the process which occurs within PCR, just slightly different.
Who confirmed conservative replication?
How did they confirm it?
Meselson and Stahl- at the time people were unsure whether DNA was replicated conservatively (if conservatively, the original strand of DNA would stay together, and the new DNA molecule would contain two new strands) or semi-conservatively (where each DNA molecule contains two different strands)
They grew two samples of bacteria with two isotopes of nitrogen 14N (light) and 15N (heavy) . One in a nutrient broth containing the light nitrogen and another containing the heavy nitrogen. The bacteria gradually used these nitrogen as resources for when they reproduced. The bacteria’s DNA were samples, placed in a centrifuge and spun, where the centrifuge showed distinct layers in each tube where the isotopes of nitrogen lay, the heavy nitrogen strands of DNA sitting nearest to the bottom, and the light nitrogen sitting nearest to the top. The bacteria were then transferred to the alternative nutrient broth, and were left to grow for one round of DNA replication. The new bacteria’s DNA was sampled, and was centrifuged. They found that the new strand of DNA sat somewhere between the two isotopes of nitrogen, meaning a mixure of differently weighted nitrogen isotopes lay in the sample. If DNA conservatively replicated, there would be still two distinct layers present, but since one existed which settled somewhere between where the light and heavy nitrogen settled, then semi conservative replication must have occurred.
What are the 5 types of DNA mutations?
Duplication
Insertion
Deletion
Inversion
Substitution
What is incomplete dominance?
Where the trait for the dominant allele isn’t completely shown, and some of the recessive allele is shown in the phenotype.
How can the chi squared test be used?
It is used to see whether the results of an experiment can be used to support the theory.
First a predicted result is calculated- this is the expected result. Then the actual result is recorded- this is the observed result.
The null hypothesis is always that there is no significant difference between the expected result and the observed result. The experimental result is usually a bit different to the expected result, but you need to know whether this is down to chance or whether this is due to your experiment being wrong.
What is the protein associate with cystic fibrosis if it is malfunctional?
How does the CFTR protein work to regulate mucus consistency?
If it is malfunctional, explain how somebody would attain thick sticky mucus.
CFTR Protein
CFTR proteins are responsible for transporting chloride ions out of cells into mucus. Subsequently, sodium ions follow
the chloride ions due to a difference in charge. The increased concentration of sodium ions causes water to diffuse by osmosis into the mucus, making it more watery. If the body detects that mucus is too watery, the CFTR proein will stop transporting so many choride ions, so less water will diffuse into the mucus by osmosis, and it will therefore thicken.
If someone has cystic fibrosis, a recessive condition ff, they will have a malfunctioning CFTR protein which is significantly less efficient at transporting chloride ions. This means that less chloride ions will be transported out of cells into mucus, meaning less sodium ion ions will follow due to a difference in charge, and therefore less water will diffuse by osmosis into the mucus. This means that the mucus will always have a thick and stick consistency.
How does having cystic fibrosis affect the:
Respiratory system
Digestive system
Reproductive system
respiratory-
respiratory system is comprised of cells called cilia, which have function to waft mucus towards the throat, where it is swallowed. This is important because mucus traps microorganisms and these may be infectious, so it crucial that they are swallowed and taken to the stomach to be destroyed. If too thick, the ciclia cannot waft the mucus, it remains within the system and builds up, potentially trapping airways, and limiting the gas exchange which can occur past the areas of blockage. Additionally, the risk of infection increases because the mucus has trapped potentially pathogenic microorganisms, and because the mucus isnt being moved, infections are more prone to occur. People with CF are given antibiotics to kill the bacteria within the microorganisms to prevent infection.
digestive-
The tube which connect the pancreas to the small intestine can become blocked with mucus. This prevents digestive enzymes produced in the pancreas from reaching the small intestine. This prevents someone with CF from being able to digest food as efficiently and therefore reduces the amount of nutrients which they are able to absorb.
Reproductive-
In men, the tubes connecting the testicles with the penis become blocked. This means that the sperm do not reach the penis. In women with CF, the eggs cannot travel as far down the oviduct because their mobility is reduced as they travel in the mucus, which in this case is thicker, so it moves slower. Additionally, if sperm were to enter past the cervix, they would become stuck in the mucus, which would not allow the sperm to reach the egg and therefore no acrosome reaction occurs etc.
describe what the three main types of genetic screening are their advantages and disadvantages respectively:
Identification of carriers
Pre implantation genetic diagnosis
Pre natal testing;
-Amniocentesis
-Chronic villus sampling
Identification of carriers:
This is offered to individuals with a family history of genetic diseases. Its useful as couples would know what the probability of their child having a disease would be. However, it may be distressing for individuals to discover this information, and the potential that the test reveals other diseases may be additionally stressful. However, these tests aren’t fully accurate and could give a false positive. Additionally, if this information was public insurance companies, and employers could not give you the same opportunities as other people- this is genetic discrimination.
Pre implantation genetic diagnosis:
This is carried out by producing embyos by IVF. The embryos are screened for genetic disorders, and this means the ones which have the genetic disorders arent implanted. This raises social and ethical issues because other characteristics can be tested for, such as eye colour, leading to trophy babies, pretty sure this happened in sweden in the 80s. Additionally, the tests can produce false positives.
Prenatal testing: This is testing on unborn babies for genetic disorders
- Amniocentesis is analysis of amniotic fluid, which is drawn with a fine needle through the abdomen, which contains fetal cells. This DNA can be analysed for genetic disorders. Amniocentesis has a 1% chance of miscarriage and can be done 15-20 weeks into the pregnancy. It provides the option for abortion. It usually takes 2-3 weeks to recieve the test, although a rapid test which would take 3-4 days woulf provide results for the most common disorders. There is however always thew risk of false positives.
Chorionic Villus Sampling is a form of sampling of the chorionic villi which are projections found on embryos early in development, which later form the placental tissue. Analysis of such tissues give information about any geentic disorders within the embryo, and provide the option for abortion. This test can be done 11-14 weeks into the pregnancy, and has a 1%-2% chance of miscarriage. There is always the chance of false positives, but the results usually take 2+ weeks to come in, but any obvious major issues can be detected in the first few days.
All are unethical in the sense that something should be aborted just because of genetic disorders.
