Genetics and Evolution (Module 6) Flashcards
What is a mutation?
A random or spontaneous change to the sequence of bases in DNA
What are the different types of mutation?
Substitution, deletion and insertion
What are substitution mutations?
When one or more nucleotides are substituted, which causes a change in codon, therefore amino acid sequence and primary structure of a protein
What is degenerate code?
When, in substitution mutations, when the codon changes it still codes for the same amino acid; so does not change the primary shape of the protein
What are insertion mutations?
When one or more nucleotides are inserted into a DNA base sequence
What are deletion mutations?
When one or more nucleotides are deleted from a DNA base sequence
What do deletion and insertion mutations cause?
Frameshifts, which has much worse effects as some genes are unfinished as codons are always 3 bases. Lots of bases also change amino acid formation
What are the three outcomes of mutations?
No outcome, damaging outcome, beneficial outcome
Name some mutagens (chemical, physical or biological agent that increases likelihood of mutation)?
Ionizing radiation, deaminating agents, alkylating agents, base analogs, viruses
What are the different types of chromosomal mutations?
Deletion, duplication, translocation, inversion
Why are chromosomal mutations worse than other mutations?
Because there are more genes condensed than are effected
What is the difference in gene expression between eukaryotes and prokaryotes?
The stimuli that trigger transcriptional enzymes to be activated
What are the different ways gene expression can be controlled?
Transcriptional, post-transcriptional, translational, post-translational
What are genes regulated by?
Protein based hormones
What are some transcriptional control mechanisms?
Chromatin remodeling, Lac Operon, Histone modification
What is chromatin remodeling in transcriptional control?
When DNA is either tightly wound into heterochromatin (so it cannot be accessed by RNA polymerase to be transcribed from) or loosely wound into euchromatin (so DNA can be accessed by RNA polymerase for transcription)
What is histone modification in transcriptional control?
DNA (negatively charged) is wrapped around positively charger histones. Acetyl or phosphate groups can be added to DNA to make the histones less positive so the DNA is wound less tight (for access for transcription), or methyl groups can be added to make the histones more positive, so DNA is bound tighter (less access for transcription)
What is Lac Operon?
A form of gene expression where a repressor protein binds to a promoter region, which prevents the binding of RNA polymerase so transcription cannot ensue. If glucose/lactose is present, it binds to the repressor- causing it to change shape and so cannot bind to the promoter region; RNA polymerase can bind for transcription.
What is the role of cyclic AMP? (cAMP)
Catalysing the lac operon mechanism to speed it up, when glucose is present, forms ATP instead to inhibits lac operon.
What are introns and exons?
Introns are non-coding DNA and exons are coding DNA
What happens during pre-translational control?
Introns are removed from pre-mRNA (splicing) and modified nucleotides are provides at both ends (5’ and 3’) to form ‘caps’ and ‘tails’.
Why does mRNA need ‘caps’ and ‘tails’?
To help stabilise the molecule and prevent degradation in the cytoplasm
What is RNA editing in pre-translational control?
When mRNA molecules have addition, deletion or substitution (point) mutations to increase the range of proteins that can be made from a single RNA molecule.
What mechanisms control protein synthesis? (transcriptional control)
Degradation of mRNA, binding of inhibitory proteins to mRNA, activation of initiation factors (aid binding of mRNA to ribosomes)
What are some mechanisms for post-translational control?
Addition of non-protein groups (carbohydrates, phosphate, lipids), modifying amino acids/formation of bonds, folding/shortening proteins, modification of cAMP
What are body plans?
A small group of genes that regulate anatomical development
What are hox genes?
A subset of homeobox genes that regulate ONLY animal anatomical development
What are homeobox genes?
A sequence of 180 bases that are involved in regulating anatomical development in animals, plants and fungi
What are homeotic genes?
An ancient family of genes involved in controlling anatomical development
What are homeodomain proteins?
Proteins that contain a homeodomain sequence, they act as transcription factors to activate or repress genes that regulate mitosis, apoptosis and the cell cycle
Give an example of a homeobox mutation
Pax6 gene, that when mutated causes blindness due to an underdeveloped retina- occurs in humans, mice and fruit flies.
How many hox genes do humans have?
39
In body plans, what is a common feature of animals?
They are segmented and have symmetry
What types of symmetry occur in animals?
Radial symmetry, bilateral symmetry, asymmetry (sea sponges)
What is apoptosis?
Programmed cell death
What is necrosis?
Uncontrolled cell death
How does apoptosis occur?
Cytoplasm and nucleus gets denser, blebbing occurs, cell chrinkage, then the nucleus ‘fragments’ and blebs break off into apoptotic bodies break off and then are engulfed by phagocytes
What is the difference between discontinuous and continuous variation?
Continuous: genetics that CAN be affected by environment and genetics, and is presented as a line graph. Discontinuous: genetics that CANNOT be affected by environment, only genetics- presented as a bar chart.
What factors can affect gene expression?
Internal: stress, hormones or psychological distress External: temperature, light intensity, drugs
How is genetic variation achieved?
Combination of gametes from parents via sexual reproduction
What is a phenotype?
The observable characteristics of an organism
What is a genotype?
Genetic make-up of an organism with respect to genes
What is the difference between homozygous and heterozygous genes?
Homozygous is when there are two of the same genes (recessive or dominant), and heterozygous is when there is one of each
Give some examples of discontinuous variation
Blood group, round/winkled pea shape, albinism
Give some examples of continuous variation
Leaf surface area, animal mass, skin colour
What is codominance?
When both genes for one characteristic are both dominant, and present themselves equally
What are autosomes?
Every other type of chromosomes other than sex chromosomes
What is sex linkage?
Characteristics determined by genes of sex chromosomes (X and Y)
List some examples of sex-linked disorders
Colorblindness, hemophilia, intersex
Why are females less likely to have sex-linked disorders?
Because they need the mutated gene on both X chromosomes, whereas males only have one X chromosome so are more likely to be a sufferer
What is haemophilia?
A sex-linked disorder that mutates the gene that forms blood clots
What is autosomal linkage?
Genes that are linked on the same chromosome and are inherited as a unit, are not separated by meiosis until chiasmata
What is the equation for recombinant frequency?
number of recombinant offspring/total offspring
What is recombinant frequency?
Measuring the amount of crossing over that happens in meiosis in a dihybrid cross
What is a dihybrid cross?
A Mendel genetic cross that determines the offspring of two linked autosomal characteristics
Determine the meaning behind the recombinant frequency equation
> 50%, no linkage. <50%, some linkage.
What is epistasis?
Interaction of genes at different loci, for example gene regulation (lac operon).
What type of variation is often linked to epistasis?
Continuous variation
How does epistasis work?
When considering genes a, b and c, gene a makes enzyme A, which catalyses a reaction at precursor a to make precursor b… and so on.
What is the difference between dominant and recessive epistasis?
If two recessive genes at a loci led to an effect on gene expression, then that is recessive epistasis. If one or both of the genes at the loci were dominant and caused an effect, then that is dominant epistasis (which can lead to masking)
What is masking in epistasis?
In dominant epistasis, the dominant allele will ‘mask’ the recessive allele in a heterozygous pair.
What is a hypostatic gene?
A gene that is affected by another gene
What is an epistatic gene?
A gene that affects another gene
What is the formula for allele frequency?
p + q = 1 p(dominant) q(recessive)
What is the Hardy-Weinberg principal?
A principal which states that ‘in a stable population with no disturbing factors, the allele frequencies will remain he same so evolution will not occur.’ This is not accurate as there commonly is no ‘stable’ population.
What are some factors that affect evolution?
Mutation, sexual selection, gene flow, genetic drift, natural selection, the founder effect (genetic drift with natural disaster)
What are density dependent and independent factors?
Limiting factors that can decrease the population, for example:
Dependent (on population size): competition, predation, disease and parasitism
Independent (of population size): climate change, natural disasters, seasonal change, human activities
What is stabilising selection?
A bell shaped graph that has the normal as the positive selection, and extremes as negative selection. Therefore the negative selective genes are reduced via natural selection… changing the allele frequency
What is directional selection?
When the most extreme phenotype variations occur more frequently due to a change in environment, such as the peppered moths (only one phenotype)
What is disruptive selection?
When both of the extreme phenotypes in a population are more frequent, which is the opposite to stabilsing selection.
