Genetics Flashcards
What is a phenotype?
It is our genotype + environment
What is the main difference between somatic cells and gametes?
Somatic cells have a diploid number of chromosomes. Gametes have a haploid number of chromosomes
What is dominance/recessiveness?
Differences in the DNA code between alleles at the same locus may give rise to dominance or recessivness which couple with sex linkage, may give rise to simple modes of inheritance.
What is the law of segregation?
The two alleles for a heritable character segregate during gamete formation and end up in different gametes
What is the law of independent assortment?
Each pair alleles segregates independently of each other pair of alleles during gamete formation
What are the phases of mitotic divisions?
Growth 1 phase
S phase – genetical replication phase
Growth 2 pahse
Mitotic phase – PMAT
Cytokinesis
What is the process of meiosis?
Meiosis is a process which reduces the chromosome number so that each daughter cell has only one of each kind of chromosome. The process of meiosis ensures that the next generation will have:
- A diploid number of chromosomes
- A combination of traits that differs from that of either parent
What are the steps of meiosis?
- A cell exist with no DNA replication
- DNA replication occurs – sister chromatids are connected by the centromere
- Non-sister chromatids may exchange genetic material – this is called synapsis – or crossing-over
- Meiosis I occurs – the homologous pairs are separated
- Meiosis 2 occurs – sister chromatids are separated
- Result - 4 different cells with haploid number of chromosomes now exists
What is the key mechanistic difference between mitosis and meiosis?
Mitosis has 1 round of division, while meiosis has 2 rounds of division.
How does meiosis create genetic variation?
At meiosis I the separation of homologous pairs creates a segregation of different locuses into different gametes. The random assortment also occurs, as pairs may line up in different assortments thus creating different pattern of creating gametes. Both Mendel’s laws are dependent on the separation of homologous pairs during meiosis I.
Where does variation come from?
- Alteration, disruption or damage to the genetic material
- Ttanscription + alternative splicing
- Recombination during meiosis
- Fertilisation
- Epigenetic factors regulating gene expression
What are the 2 types of alterations?
- Somatic – only affects the host.
- Germline - may affect the offspring.
What causes of point mutations?
Causative agents – internal during process of replication and repair, chemical, ionizing radiation, viral.
What does the accumulation of point mutation cause?
The accumulation of point mutation may cause an alteration in protein structure.
What are some of the sources of chromosomal variation?
- Deletions/Insertions
- Amplification
- Translocation
- Aneuploidy
What are the three checkpoint in cell cycle?
- G1 prior to S
- During G2 prior to M phase
- At the end of M phase
Where does the exchange of genetic material occur during synapsis?
It occurs on non-sister chromatids.
What are the genetic and phenotypic outcomes from single gene segregation in pure breeding parents?
The potential traits of the offspring can be predicted.
What is the mendell’s law of segregation?
In a heterozygous organism the two different alleles will be separated during meiosis.
What happens to two different genes on the same chromosome?
If no crossover changes, the F2 progeny may have a very limited coupling and repulsion.
How do we overcome the issue of genes being on the same chromosome?
Crossing over or synapses – this resolves the independent assortment of genes on the same chromosome by inducing an exchange in genes from two non-sister chromatids.
What is the main difference between assorting independently and complete linkage of genes?
When assorting independently, the genetic variation is considerably greater than when there is no crossing over occurring
What is the difference between coupling and repulsion?
Coupling reference to inheritance of two dominant or two recessive genes. Repulsion is an inheritance of one dominant and one recessive gene.
What can we say about the events of synapsis of two genes that are not close to each other?
They are more likely to undergo synapses, if 2 genes are not next to each other thus undergo recombination e.g. polar ends of the chromosome.
What is the recombination frequency?
It is the proportion of recombinant phenotypes to the total phenotypes is called recombination frequency. It is calculated by combining all instance of the phenotype and dividing by all sample taken. This can also be used to calculate the genetic map distance, just multiply the recombination frequency by 100.
What are homeobox genes?
They are genes that regulate the development of structure in the embryo. They perform they are functions on and off and are unequally distributed throughout the embryo in terms of effect.
What are transcription factors?
They are molecules that upregulate or downregulate the activity of certain genes
What is development?
It is a combination of proliferation, migration and differentiation
What are morphogen gradients?
They are positional cues for cells during development; this establishes cell signalling networks to control gene expression
What are the steps of embryogenesis?
- Fetilisation
- Induction, competence, differentiation
- Formation of the three layered embryo
- Formation of neural crest cells
- Folding of the embryo
What are growth factors?
They are inter-cellular signalling mechanism. They promote cell growth, differentiation and maturation. Produced at 2 cell stage. They also control gene expression.
What are homeobox genes?
They are key genes, that are usually the first genes to cause differentiation. They actually DNA sequences found within genes that are involved n the regulation of patterns of anatomical development. These transcription factors typically switch on cascades of other genes.
What are hox genes?
It is a group related genes that determine the basic structure and orientation of an organism. They are critical for proper placement of segment structures. Most are linked together in sequential clusters. This means that there is not much synapsis occurs relating homeobox genes.
What is the objective of homeobox genes?
Create a transcription factor and start a transcription cascade
What are morphogenetic field?
It is a protein concentration that drives morphological change.
How many homeobox clusters are there?
4 – C-7,-17,-12 and -2.
With current technologies, how long and how much does it cost to sequence a single human genome?
It costs under $1000 and takes under 8 hours.
What are some of the potential treatments we might have available soon in the field of genetics?
- Genetic engineering
- Gene therapy
- Genetic testing and counselling
What are the potential use of genetic engineering in dentistry?
- Growing new teeth in vitro/in vivo
- Stem cell therapy for periodontitis
- Changing the oral ecology
What can genetic testing reveal?
- DNA sequence information
- Specific genes present in the individual
What is a gene pool?
It is a set of genetic information (all alleles) carried by the members of a sexually reproducing population.
What can you comment on the variation in regards to population genetics?
Variation is even more important in population genetics, as it allows for a larger number of individuals to be adapted to certain events thus making them more likely to survive and reproduce.
What is monomorphic?
When there is 1 gene in a allele
What is dimorphic?
When there are 2 genes in an allele
What is a polymorphic gene?
It is 1 allele that is present in at least 1% of the population
How do you calculate genotype frequencies?
Occurrence divided by total number
How do you calculate allele frequencies?
Times the occurrences by 2 and remember that heterozygous individuals need to be separated into 2 different alleles
What is a Hardy-Weinberg equilibrium law?
It is a law that is used to calculate allele frequencies in non-evolving populations, with assumption that shuffling of alleles has no effect on the overall gene pool. Deviations from this law result in evolution. Due to limitations above this law cannot be used in natural populations but it help us to understand how the evolution occurs.
What are the necessary conditions for Hardy-Weinberg equilibrium?
- No new mutations
- No migration in or out of the population
- No selection
- Random mating
- Very large population
