gene mutations + inheritance Flashcards
genetic mutations definition
a change in the sequence of bases in a DNA molecule that may result in an altered amino acid sequence
why do genetic mutations occur
they can occur spontaneously + randomly during DNA replication, or as a result of mutagens
mutagen definition
something that increases the chance of a gene mutation
give 6 examples of mutagens
- ionising radiation e.g. x-rays
- deaminating chemicals
- viruses inserting sections of viral DNA
- smoking
- age
- caffiene
what are the 3 types of mutations
substitution
insertion
deletion
substitution mutation definition
a type of mutation where a base in a DNA sequence is swapped out for another one
what are the 3 types of substitution mutations
nonsense - mutation changing an amino acid to a premature stop codon
missense - mutation alters a single amino acid e.g. sickle cell anemia
silent mutations - mutations that have no effect
give 3 reasons why silent mutations occur
- genetic code is degenerate, meaning many triplet codons code for the same amino acids, so a mutation in the base sequence may not effect the amino acid sequence
- protein may only be changed slightly, or not on the active site, so the function is mostly unaffected
- the mutation could impact non coding DNA, so no amino acid sequences are affected
why are insertion or deletion mutations often much more dangerous
these mutations cause frame shifts. meaning every codon after the mutation changes, including stop codons
what are the potential effects of mutations + examples
neutral - normal functioning proteins are still synthesised, or any changed are not harmful e.g. polydactyly or silent mutations
harmful - proteins are non functional or not synthesised e.g. cystic fibrosis or photooncogenes changed to oncogenes, which are cancer causing
beneficial - proteins have useful new characteristics or work better e.g. production of melanin which protects from UV
locus definition
the point on DNA where a specific gene is found
regulatory genes
genes that control what genes are expressed in what cell at what time - all nuclei in an organism contains the same DNA, this is what allows some cells to have specific functions
what are the 3 types of regulatory gene
pre-transcriptional level regulation
transcriptional level regulation
post-transcriptional level regulation
structural genes definition
sections of DNA that code for proteins that have a function within a cell e.g. enzymes, membrane carriers
regulatory genes definition
sections of DNA that code for proteins / transcription factors which control the expression of structural genes
transcription factors
proteins that bind to DNA and switch on and off genes by increasing or decreasing rate of transcription - they can be activators or repressors
how do transcription factors work
they bind to promoter regions of a gene, which either allows or prevents transcription of the gene - this binding will either increase or decrease transcription rate
control elements definition
areas of DNA that are either promoters or operators
promoters = RNA polymerase binds to it
operators = transcription factors bind to it
operon definition
sections of DNA containing a cluster of genes controlled by the same promoter - they are found mostly in prokaryotes
what is an example of a transcriptional level regulatory mechanism
the lac operon in E.coli
what is the function of the lac operon
this controls the production of structural proteins within E.coli, for example the enzyme lactase
it ensures lactase is only synthesised when lactose is present
inducible enzyme definition + an advantage
enzymes whose expressions are regulated, e.g. lactase in E.coli
- this helps prevent waste of materials / energy
describe the structure of the lac operon
the gene contains many regions:
P lacI { P O lacZ lacY lacA }
{ the lac operon }
P - the promotor for the regulatory gene
lacI - the regulatory gene, this is always on, it codes for the repressor protein
P - the promotor for the structural gene
O - operator region
lacZ - the lactase gene
lacY - the gene which codes for proteins that lets lactase into the cell + codes for permease
lacA - the gene that codes for transacetylase
- these 3 lacZ / lacY / lacA regions get switched on and off
what happens to the lac operon when lactose is absent
- the regulatory gene lacI is transcribed and translated to produce the lac repressor protein
- this protein binds to the operator region
- due to the lac repressor protein, RNA polymerase cannot bind to the promotor region
- therefore transcription of the structural genes lacZ/lacY/lacA cannnot take place
- no lactase is synthesised
what happens to the lac operon when lactose is present
- lactose binds to the repressor protein, distorting its shape
- the repressor protein can no longer bind to the operator region
- RNA polymerase binds to the promotor region
- transcription of the lacZ/lacY/lacA genes takes place
- lactase is produced
what feature must the lac repressor protein have to be able to function
it must have 2 binding sites as it must be able to bind to both the operator region and also to lactose
introns definition
a section of DNA that does not code for a protein
exons definition
a section of DNA that does code for a protein
pre-mRNA definition
this is the form of mRNA right after transcription of a gene has taken place - this contains both introns and exons
what happens to introns + how
introns are removed from pre-mRNA via splicing - this is a form of post-transcriptional modification
outline the process of splicing
- pre-mRNA contains both introns and exons
- a spliceosome forms and binds to the mRNA and causes the introns to form a loop shape
- the intron is excised and the exons are then attached together
- this forms mature mRNA, containing only exons, which is ready for translation
hox genes definition
a class of homeobox genes found only in animals
involved in the formation of anatomical features in the correct locations of the body plan
also code for homeodomain proteins
homoebox genes definition
genes that contain highly conserved regions of DNA, made of a sequence of 180 base pairs involved in regulating anatomical development in plants, animals and fungi
they also code for homeodomain proteins
homeodomain proteins definition
proteins that act as transcription factors to activate/repress developmental genes that regulate mitosis, apoptosis and the cell cycle
what organisms have been used to investigate hox genes + why
fruit flies as they are much simpler than humans - have 1 set of hox genes as opposed to 4, and they are easy to keep, and have a short life cycle
how does the structure of hox genes relate to their functions in the body
generally genes active in the head lay at one end, genes affecting the tail lay at another end, and genes affecting the middle are inbetween
homologous structure definition
between organisms, many body parts have the same underlying structure, although they may appear different or have different functions
apoptosis definition
programmed cell death - this is how humans get fingers and toes
outline the importance of apoptosis and mitosis in human development
during embryonic development:
mitosis creates the bulk of the tissue
apoptosis then refines them by removing unwanted structures / tissue segments
during later stages of life:
apoptosis of older cells is necessary to make room for healthy new cells
- without this cancers can form
how does apoptosis and mitosis change as we age
as we age our tissues are degenerating, so more apoptosis is occurring than mitosis, this causes general deterioration, e.g. worse hearing, sight, etc
give 3 internal factors that affect apoptosis
- genetic damage/mutations
- cell signalling molecules e.g. hormones, growth factorss
- psychological stress
give 4 external factors that affect apoptosis
- pathogen attacks
- drugs
- temperature / light intensity
- malnutrition
outline how cell apoptosis works
1- cell starts to bleb and nucleus disintegrates
2- cell fragments are produced with membranes surrounding/enclosing them
3- phagocyte engulfs the cell
4- the cell is broken down by lysosomes
5- break down products are either recycled of excreted
give an example of cells that play a role in cell death
kupffer cells are a type of phagoctye in the liver are involved in the death of red blood cells
spatial linearity definition
refers to the lay out of hox genes, that genes at the top code for the head, genes at the bottom code for tail, etc
temporal order definition
the order that hox genes are coded in - first the head genes, then the middle, then the tail/bottom genes
case study - disruption of hox genes
- what caused it
- what did it do to hox genes
- consequences
thalidomide - a drug prescribed to pregnant women for morning sickness
- it affected homeobox genes at a critical stage of embryonic development, impacting forelimb development in babies as a side effect
- resulted in thousands of babies being born with severe deformities
what is thalidomide used for now
used to treat some cancers, the property that once caused problems is being used to stop tumour development
- it works by preventing capillary network formation which are essential for tumours to develop + grow
what are the 2 types of species variation
interspecific - between species
intraspecific - within a species
what are the 2 types of variation
continuous - controlled by many genes and often affected by environment, e.g. height
discontinuous - controlled by just one gene, e.g. eye colour, blood type
how does sexual reproduction facilitate the increase of variation
- production of gametes in meiosis as a result of crossing over + independent assortment
- random fertilisation of 2 unique gametes
sex linkage definition + 2 examples
refers to genes found on a certain sex chromosome - X or Y
e.g. colourblindness, haemophilia
what gender is more commonly affected by sex linked conditions + why
males - this is because any condition linked to X or Y will be expressed as there is only 1 of each
women have 2 X chromosomes, so if only 1 has a gene for a specific condition, it will be masked by the second one, for the allele to be expressed both X chromosomes must have the allele for the condition
autosomal linkage definition
refers to characteristics linked to a non sex chromosome
autosome definition
a non sex chromosome - pairs 1-22
dominant vs recessive
dominant = an allele that is always expressed if present
recessive = an allele that is only expressed if homozygous
what is the expected phenotypic ratio for a monohybrid heterozygous cross
e.g. Rr + Rr
3 : 1
what is the expected phenotypic ratio for a monohybrid homozygous cross
e.g. RR + rr / RR + RR / rr + rr
they will all be the same
what is the expected phenotypic ratio for a dihybrid homozygous cross
e.g. YYRR + yyrr
9 : 3 : 3 : 1
what is the expected phenotypic ratio for a dihybrid homozygous cross for genes displaying dominant epistasis
12 : 3 : 1
what is the expected phenotypic ratio for a dihybrid homozygous cross for genes displaying recessive epistasis
9 : 3 : 4
how does autosomal linkage occur
2 characteristics can become linked if they are close together on the chromosome, as they are less likely to become separated by crossing over, and they will stay together during independent assortment
- this can change expected phenotypic ratios
epistasis definition + 2 examples
when a gene isn’t visibly expressed as it is dependent on another gene - the unexpressed gene would be epistatic
e.g. widows peak isn’t seen if bald
black stripes on black cat appears solid black
what is the difference between dominant and recessive epistasis
dominant = when the 1st gene is dominant over the second gene
recessive. = when the 2nd gene is dominant over the 1st gene
genome definition
all the genes within an organism
genetic drift definition
idea that chance events affects which individuals in a population survive + breed + pass on alleles
- this affects small populations more
allele frequency definition
how often a particular allele occurs in a population
genetic diversity definition
variation of alleles available
give 3 ways to increase genetic diversity
- mixing populations of the same species from different areas
- increasing reproduction / mutations from meiosis
- random mating, no restrictions
give 2 ways to decrease genetic diversity
- selective breeding / captive breeding
- isolating species into smaller populations
directional selection definition + example
selection pressures push evolution in a certain direction
e.g. lower temps favour longer fur, so those with long fur survive and reproduce, shorter fur dies out, over time fur length increases
stabilising selection + example
selection pressures favour an average
e.g. temp stops dropping so average fur length is favoured
species definition
a group of organisms with similar characteristics that can produce fertile offspring
what are the 2 types of speciation
allopatric speciation
sympatric speciation
allopatric speciation definition
geographic isolation of a single species causes variation between separated populations, until the 2 species evolve apart / diverge over time
sympatric speciation definition
various other factors cause reproductive isolation within a species, resulting in the evolution of 2 separate species over time
- these factors could be behavioural changes, habitat preferences, physical differences
outline the process of allopatric speciation
1- geographical changes cause reproductive isolation
2- random allele frequencies in separated populations would result in greater variation between species
3- random allele mutations also contribute to this changing variation
4- different selection pressures cause further differentiation between groups
5- over time the groups become so genetically different that reproduction is not possible as gametes are incompatible
founder effect definition
the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population - this can cause traits that are usually rare to see become common due to random allele frequencies, also the new population would suffer from the effects of inbreeding, decreasing the gene pool and increasing mutations
genetic bottleneck definition
this occurs when a population is greatly reduced in size, limiting the genetic diversity of the species, as many alleles would have been lost
- this could be the result of a natural disaster
what is the purpose of the hardy weinburg principle
used to predict the proportion of dominant + recessive alleles in a population
what are the 5 assumptions made when using the hardy weinburg principle
- no selection
- no mutations
- no migration
- large sample size
- random mating
cannot be truly representative of real life as these aren’t guaranteed
