Genetics Flashcards
What is the relationship between the degree of crossing over and the distance between two genes?
It is direct; as the distance increases, the frequency of recombination increases.
In a three-point mapping experiment what three general classes of offspring are expected (assuming crossovers occur)?
Non-crossovers
Single crossovers
Double crossovers
In a three point mapping experiment how many different genotypic classes are expected? (assuming crossovers occur)
8
What are the main checks performed by the G2/M checkpoint?
DNA replication has been completed and any DNA damage has been repaired
Do all cells that enter G0 come back to the cell cycle at some point?
No, most differentiated cells in multicellular organisms remain in G0 phase indefinitely. Some, such as cardiomyocytes or motoneurons, once they are terminally differentiated in the adult never re-enter the cell cycle.
What would be the consequence of a defective M checkpoint?
The most likely outcome will be unequal separation of chromosomes, with a daughter cell receiving more chromosomes than the other.
What do you think is the point of having a G0 in pluricellular organisms?
It allows for terminal specialization of cells or for some type of cells re-entering the cell cycle under special circumstances, for example when regeneration is required, as we explained is the case with satellite cells and skeletal muscle.
What would be the consequence of a defective G1/S checkpoint?
It may allow DNA replication to proceed even if DNA is damaged, leading to an accumulation of mutations in the daughter cells. If these mutations affect the very genes that control the regulation of the cell cycle, cells may divide uncontrollably. This is the underlying cause of many forms of cancer.
Assume that the G1 nuclear DNA content of a species is 30 picograms. What would be the expected DNA content in a somatic cell going through metaphase?
In metaphase the chromosomes have already replicated and ready to be split at the centromere, but the cell has not yet divided and therefore contains double the amount of the DNA, i.e. 60 picograms
There are two rounds of division during meiosis, and yet the amount of DNA is only halved.
When has DNA replication occurred?
Interphase, before prophase I
When does synapsis between homologous chromosomes occur?
Paquinema.
What structure is required for the chromosomes to synapse?
The synaptonemal complex.
What are chiasmata and when are they visible?
Chiasmata are places where non-sister chromatids remain bound and are thought to represent the place where DNA exchange took place during the process of crossing over. They are visible during diplonema.
Define zygonema
Zygonema is the sub-stage where synapsis between homologous chromosomes begins.
In a prokaryotic gene, what is an operator?
The region where RNA polymerase binds
What is allostery?
Changes in the structure and function of a protein triggered by the binding of a small molecule
What mutation could give rise to constitutive expression of the lac operon?
Deletion of the lacI gene. If the gene is deleted then the repressor protein will be absent and so there will be no repression of the lac operon (i.e there will be constitutive expression)
