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 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?
A homeobox gene is a type of gene containing a DNA sequence called a homeobox that encodes a homeodomain protein, which acts as a transcription factor to regulate the expression of other genes during development, particularly in establishing body plans and segmentation in organisms.
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
What are the key steps ocurring during Meiosis?
Meiosis involves the same four phases seen in mitosis. They occur during both meiosis I and meiosis II. The period of time between meisosis I and meiosis II is called inter-kinesis. No replication of DNA occurs during inter-kinesis because the DNA is already duplicated.
Compare and contrast mitosis and meiosis
Mitosis produces two identical diploid cells for growth, repair, and asexual reproduction, maintaining chromosome number and genetic consistency in somatic cells, while meiosis generates four diverse haploid gametes for sexual reproduction, halving chromosomes and introducing variation through crossing over and independent assortment in germ cells. Both share stages like prophase and metaphase but differ in division number (one for mitosis, two for meiosis), chromosome dynamics, and outcomes, with mitosis ensuring uniformity and meiosis driving evolutionary diversity.
Mitosis and meiosis, both preceded by a single DNA replication in interphase, are cell division processes with distinct roles: mitosis, requiring one division, produces two genetically identical diploid daughter cells in somatic cells for growth and repair, while meiosis, involving two divisions, generates four genetically diverse haploid gametes in reproductive organs for sexual reproduction, halving chromosomes and introducing variation through crossing over and independent assortment
Describe the relationship between Mendel’s Law and Meiosis.
Mendel’s observations ( and his law) are a consequence of events that occur during gamete formation - meiosis.
Describe how meiosis supports new genetic variations
There are two sources of genetic recombinations during meiosis:
1. crossing-over: non-sister chromatids of a chromosome pair exchange their genetic material
2. Independent assortment: homologous chromosomes are distributed to daughter cells randomly
Both events assure new genetic combinations in the offspring. Fertilisation between haploid gametes result in a third source of genetic recombination because there is the combining chromosomes from different individuals.
Determine a cell’s position in the meiotic cycle from its chromosomes and gene copy number
What determines phenotype?
Genotype and environment
What is the purpose of genetics?
High fidelity information transfer
What is the basic unit of inheritance?
Gene
What are genes arranged on?
Chromosomes (circular or linear)
What is DNA and what’s its significance?
Genes / chromosomes are made of DNA
DNA is sugar-phosphate backbone + nucleic acid ‘code’ (A, G, C, T)
DNA is is a linear macromolecule with 3 main functions:
- Protein synthesis (transcription & translation)
- Self-replication (cellular / organism)
- Inter-generational information transfer
Describe the relationship between Dominance/Recessiveness and Sex Linkage
Differences in the DNA code between alleles at the same locus give rise to Dominance / Recessiveness and this, sometimes coupled with sex linkage, may give rise to simple modes of inheritance.
Describe the key concepts of Mendel’s Law
- Alternative versions of genes account for variations in inherited characters
- For each character, an organism inherits two alleles, one from each parent (ONLY TRUE FOR DIPLOID ORGANISMS REPRODUCING SEXUALLY)
- If two alleles at a locus differ, then one, the dominant allele, determines the organisms’ appearance; the other, the recessive allele, has no noticeable effect on the organims’s appearance.
What are the two fundamental laws of Mendel’s Law?
- The law of segregation -> The two alleles for a heritable character segregate during gamete formation and end up in different gametes.
- The law of independent assortment -> Each pair of alleles segregates independently of each other pair of alleles during gamete formation.
Why is cell division necessary?
- Reproduction (prokaryotes) -> meiosis
- Growth (eukaryotes) -> mitosis
- Maintenance and repair (eukaryotes) -> mitosis
What is Gametogenesis?
It is required for sexual reproduction in eukaryotes
Describe Meiosis (gametogenesis)
Meiosis reduces the chromosome number so that each daughter cell (gamete) has only one of each kind of chromosome.
The process of meiosis ensures that the next generation will have:
1. a diploid (2n) number of chromosomes
2. a combination of traits that differs from that of either parents
What happens during Meiosis I?
Separates the homologous pairs of chromosomes.
- Daughter cells are haploid, but chromosomes are still in duplicated condition.
- Synapsis occurs during meiosis I
What happens during Meiosis II?
Separates sister chromatids
- The completely haploid daughter cells mature into gametes
- Fertilisation restores the diploid number of chromosomes during sexual reproduction
What is n and c?
“n” represents the number of chromosome sets (haploid number, e.g., n=23 in humans), while “c” denotes the DNA content, which doubles after replication (e.g., 2c in G2 phase).
What is a chromatid?
A chromatid is one of the two identical copies of a replicated chromosome, joined at the centromere, that separate during cell division to become individual chromosomes in daughter cells.
What are the major differences between mitosis and meiosis, both mechanically and functionally?
Mitosis and meiosis differ mechanically and functionally in key ways. Mechanically, mitosis involves one division, producing two diploid cells, with chromosomes aligning as single chromatids in metaphase and sister chromatids separating in anaphase, while meiosis requires two divisions (meiosis I and II), yielding four haploid cells, with homologous chromosomes pairing and crossing over in prophase I, aligning as pairs in metaphase I, and separating in anaphase I, followed by sister chromatid separation in meiosis II. Functionally, mitosis occurs in somatic cells to produce genetically identical cells for growth, repair, and asexual reproduction, maintaining the chromosome number (2n) and DNA content (2c post-replication), whereas meiosis occurs in germ cells to form gametes for sexual reproduction, halving the chromosome number (n) and DNA content (c) per cell, and introducing genetic diversity through crossing over and independent assortment.
What is Mendel’s second law and where does it occur in meiosis?
Mendel’s Second Law, the Law of Independent Assortment, states that alleles for different traits segregate independently during gamete formation, provided the genes are on different chromosomes. This occurs during meiosis I, specifically in metaphase I, when homologous chromosome pairs align randomly at the metaphase plate, allowing each pair to assort independently of others, leading to genetic variation in the resulting gametes.
What is Mendel’s First Law and where does it occur in meiosis
Mendel’s First Law, the Law of Segregation, states that each individual has two alleles for a given trait, and these alleles segregate (separate) during gamete formation, so each gamete carries only one allele. This occurs during meiosis I, specifically in anaphase I, when homologous chromosomes (each with two sister chromatids) are pulled apart to opposite poles, ensuring that each resulting gamete receives only one chromosome—and thus one allele—of each homologous pair.
How is Mendel’s Law derived experimentally?
Mendel’s Laws were derived experimentally by cross-breeding pea plants with distinct traits, observing inheritance patterns in offspring over generations, and analyzing ratios of phenotypes to formulate the principles of segregation and independent assortment.
Define P, F1 and F2
P is the parental generation, F1 is the first filial generation (offspring of P), and F2 is the second filial generation (offspring of F1 crosses) in genetic breeding experiments.
Use Punnet squares to exmaine allele transmission for biallelic phenotypes
Describe the concepts of coupling and repulsion
Coupling refers to linked genes on the same chromosome inherited together (e.g., AABB producing AB gametes), while repulsion describes opposite allele combinations on the same chromosome (e.g., AAbb producing Ab gametes), affecting inheritance patterns in progeny.
Describe how genes on the same chromosomes are physically linked
Genes on the same chromosome are physically linked because they reside on the same DNA molecule, tending to be inherited together unless separated by crossing over during meiosis, with closer genes having lower recombination rates.
Explain that synapsis / crossing over can resolve Mendel’s Laws for genes on the same chromosome
Synapsis and crossing over during meiosis I shuffle linked alleles via genetic exchange, enabling independent assortment and creating new allele combinations for genes on the same chromosome.
Explain why the closer two genes are on a chromosome, the lower the chance of crossover event recombining gene/allele combinations during meiosis
Closer genes on a chromosome have a lower chance of crossover because the physical distance between them reduces the likelihood of a recombination event occurring during meiosis, keeping their allele combinations intact.
Explain the expected frequencies for a biallelic cross assorting independently or under complete linkage
For a biallelic cross assorting independently (e.g., AaBb x AaBb), phenotypic frequencies are 9:3:3:1 (dihybrid) or 3:1 (monohybrid), while under complete linkage, only parental phenotypes (e.g., AB/ab or Ab/aB) appear in F2, with frequencies reflecting parental combinations (e.g., 3:1 for coupling, 1:1 for repulsion in test-cross).
Explain the concept of a test-cross/back-cross
In a test-cross or back-cross, an organism displaying a dominant phenotype but with an unknown genotype is mated with a homozygous recessive individual, allowing the offspring’s phenotypic ratios—either all dominant (indicating homozygous dominant) or a 1:1 dominant-to-recessive ratio (indicating heterozygous)—to reveal the unknown genotype, providing a critical tool in Mendelian genetics for mapping inheritance patterns and studying gene linkage.
Explain the idea of parental and recombinant phenotypes
Parental phenotypes are traits in offspring that precisely match those of the parents due to inheriting identical allele combinations without recombination, whereas recombinant phenotypes are novel trait combinations arising from crossing over during meiosis, which shuffles alleles between homologous chromosomes to produce new genetic configurations distinct from the parental types.
Explain the simple rules that enable us to apply this to simple breeding experiment
To apply a test-cross or back-cross in a simple breeding experiment, select an individual expressing a dominant phenotype but with an unknown genotype (homozygous dominant AA or heterozygous Aa), mate it with a homozygous recessive individual (aa), and observe the offspring’s phenotypes: if all offspring display the dominant trait, the tested individual is homozygous dominant (AA); if the offspring show a 1:1 ratio of dominant to recessive traits, the tested individual is heterozygous (Aa), leveraging Mendel’s laws of segregation and the predictable inheritance patterns of single-gene traits.
What are the different types of point mutations in the genetic code, their causes and their outcomes in terms of protein structure?
Point mutations include silent, missense, and nonsense mutations, caused by internal replication errors, chemicals, ionizing radiation, or viruses, resulting in no change, altered amino acid sequences, or truncated proteins, respectively, affecting protein structure and function.
What are the internal regulators of DNA replication in the cel cycle?
Internal regulators of DNA replication in the cell cycle include cyclins and cyclin-dependent kinases, which control progression through G1, G2, and M phase checkpoints to ensure accurate DNA synthesis and repair.
What are the external regulators of DNA replication in the cell cycle?
External regulators of DNA replication include environmental factors like cell size and DNA damage signals, which influence checkpoint activation during G1, G2, and M phases to prevent replication errors.
What can happen if internal and external regulators of DNA replication in the cell cycle fail?
Failure of internal and external regulators can lead to unrepaired DNA damage, replication errors, or improper chromosome segregation, resulting in mutations, chromosomal instability, or cell cycle dysregulation, potentially causing diseases like cancer.
How does mutation contribute to generating new phenotypic variation?
Mutations, such as point mutations or chromosomal rearrangements, introduce genetic variation by altering DNA sequences or gene arrangements, which can lead to new protein functions or structures, thereby generating novel phenotypic traits subject to natural selection.
What are the different sorts of chromosomal rearrangements that can occur (structure/number)?
Chromosomal rearrangements include structural changes like deletions, insertions, amplifications, and translocations, and numerical changes like aneuploidy due to non-disjunction, altering chromosome structure or number.
What are the regulation of the cell cycle and how defective checkpoints can give rise to chromosomal errors?
The cell cycle is regulated by checkpoints in G1, G2, and M phases, controlled by cyclins and kinases, but defective checkpoints can allow unrepaired DNA damage or improper chromosome segregation, leading to chromosomal errors like aneuploidy or translocations.
What are the differences between germline and somatic changes in genes / chromosomes, expecially in the context of disease?
Germline changes in genes or chromosomes occur in reproductive cells, are heritable, and can predispose offspring to diseases like cancer, while somatic changes occur in non-reproductive cells, are not inherited, and may cause diseases like tumors in the affected individual.
Triplets encode specific amino acids with a degree of redundancy - why is this important?
it minimizes the harmful effects that incorrectly placed nucleotides can have on protein synthesis.
Humans have 23 pairs of chromosomes and ~20,000 genes. Where might this macro genetic variation have originated?
Macro genetic variation, such as humans having 23 pairs of chromosomes and ~20,000 genes, likely originated from chromosomal rearrangements, gene duplications, and mutations accumulated over evolutionary time, contributing to speciation and genetic diversity.
Some genes/loci are invariant in the population, some are bi-allelic and some are poly-allelic … sequence differences in DNA. Where does this ‘micro’ sequence variation come from?
Micro sequence variation in genes/loci, leading to invariant, bi-allelic, or poly-allelic states, originates from point mutations (SNPs, duplications, indels) caused by internal replication errors, chemical agents, ionizing radiation, or viral influences.
What are the possible causes of alteration, disruption or damage to the genetic material?
- Genetic codes (A, C, G, T), allelic variation
- Gene copy number; chromosomal rearrangement
Where do alleles come from?
- Point mutations (SNPs, duplications, indels)
What are the checkpoints of the cell cyle?
The cell cycle checkpoints occur during G1 (assessing cell size and DNA damage), G2 (checking DNA damage and replication completeness), and M phase (verifying chromosome attachment to the spindle), ensuring proper progression and genome stability.
