6.2 Patterns of Inheritance Flashcards
What is a genotype?
Genetic make up of an organism
What is a phenotype?
Visable characteristics of an organism.
What is an organisms phenotype influenced by?
It’s influenced by it’s genotype and it’s enviroment.
What is a mutagen?
Physical and chemical agents that can increase the rate of mutations.
What are soome examples of physical mutagens?
- X-rays
- Gamma rays
- UV light
What are some examples of chemical mutagens?
- Benzopryene (found in tobacco smoke)
- Mustard gas
- Nitrous acid
- Aromsstic amines- in some synthetic dyes
- Reactive oxyegn species
- Colchicine
What are some examples of biological mutagens?
- Some viruses
- Transpoons- jumping genes, remnants of viral nucleic acid that have become incorporated into our genomes.
- Food contminants such as mycotoxins from fungi, e.g. aflatoxins in contaminated nuts, chemicals in charred meat and alcohol.
How can mutations that occur during gamete formation be described as?
- Persistent: they can be transmitted through many generations without change.
- Random: they are not directed by a need on the part of the organism in which they occur.
What gene mutations may occur during meiosis?
- Deletion
- Inversion
- Translocation
- Dublication
- Non-disjunctional
What is a deletion gene mutation in meiosis?
Part of a chromosome, containing genes and regulatorey sequences are lost.
What is an inversion gene mutation in meiosis?
A section of a chromosome may break off, turn 180° and then join again; although all the genes are still there, some may now be too far away from the regulatory nucleotide sequences to be properly expressed.
What is a translocation gene mutation in meiosis?
A piece of chromosome breaks off and then becomes attatched to another chromosome. This may interfere with the regulation of genes on the translocated chromosome.
What is a dublication gene mutation in meiosis?
A piece of a chromosome may be dublicated. Overexpression of genes can be harmful, because too many certain proteins or gene-regulation nucleic acids may disrupt metabolism.
What is a non-disjunction gene mutation in meiosis?
One pair of chromosomes or chromatids fails to separate, leaving one gamete with an extra chromosome. When fertalised by a normal hapoid gamete, the resulting zygote has one extra chromosome.
Downs symdrome, or trisomy 21, is caused by non-disjuction.
What is aneuploidy?
The chromosome number is not an exact multiple of the haploid number for that organism. Sometimes chromosomes or chromatids fail to separate during meiosis. (e.g. trisomy)
What is polyploidy?
If a diploid gameteis fertalised by a haploid gamete,. the resulting gamete will b y a triploid (it has three-sets of chromosomes). The fusion of two diploid gametes can make teraploid. Many cultivated plants are polypoidy.
During meiosis, how does, genetic variation occur?
- **Allele shuffling **(swapping of alleles between non-sister chromatids) during crossing over in prophase 1.
- Independent assortment of assortment during metaphase/ anaphase 1
- Independent assortment during metaphase/ anaphase 2.
- Random fusion of gemetes.
What are some examples of enviromental factors affecting an organisms phenotype?
- Speaking with a particular reigional dialect.
- Losing a limb, a didgit or getting a scar following an ingury.
What is an example of varitation by the enviroment interactibg with genes?
If plants are kept in dim light after germination, or if the soil in which they are grown contains insufficient magnesium, then the leaves do not develop enough chlorophyll and are yellow or yellow-white.
The plant is described as chlorotic, or suffereing with chlorosis. The plant cannot photosynthesis. Chlorotic plant have a geomone for making chlorophyll, but enviromental factors are preventing the expression of these genes.
What is an allele?
A version of a gene
What does hetrozygous mean?
Not true-breeding; having different allels at a particular gene locus on a pair of homologous chromosomes.
What does homozygous mean?
True-breeding; having identical alleles at a particular gene locus on a pair of homologous chromosomes.
What does monogenic mean?
Determined by a single gene
What was Gregor Mendels investigation that would lay the foundations for genetics?
Mendel studdied pea plants because trhey were easy to grow and self fertalising which made them easy to cross-fertalise artifically.
He worked with 7 characteristics, each characteristic each having 2 distictly contrasting traits:
* Stem height
* Seed shape
* Seed colour
* Pod shape
* Pod colour
* Flower arrangement
* Flower colour
When doing his investigation, when did Mendel obtain true-breeding strains?
He obtained true-breeding strains, where the trait had appeared unchanged generation after generation, from local seed merchants.
Describe Mendels simplest experiment?
It involoved only one characteristics with one pair of contrasting traits. He mated individuals from 2 parent strains, each of which showed a different phenotype. One parent was trure-breeding for tall stems and one was true-breeding for short stems. All the offspring from this cross, the F1 gemeration, werec phenotypically identical to one parent type- they were all tall. The F1 generation then self fertalised, resulting in F2 generation containing 3 times as mant tall plants to short plants.
During a monohybrid cross, what does P1 stand for?
The parental generation
During a monohybrid cross, what does F1 stand for?
First filial generation
During a monohybrid cross, what does F2 stand for?
2nd generation
In pea plants, why is the charateristic of height monogenetic?
The pea plants height is governed by one gene that has 2 distinct alleles, T/t.
What is the genotype tt called?
Recessive homozygous
How can the outcomes of monogenetic inheritance be visualised?
In punnet squares
What are test crosses for?
To determine the genotype of phenotypically similar individuals.
What is artificial selection?
Selective breeding of organismas; invloves humans choosing the desired phenotypes and interbreeding those pheonotypes individually, therefore selecting the genotypes that contibuite to the gene pool of the next generation of these organisms.
What is the agent of artificial selection?
The enviroment.
What are the agaents of artifical selection?
Humans
Wat will breeders do to create artifical selection?
They will select individuals with the desired traits and allow then to interbreed, whilst at the same time preventing those without the desired chracteristics from breeding.
What are desirable characteritics for artificial selection for plants?
- Increased yeild
- Pest and disease resistance
What are desirable characteristics to selectively breed in livestock?
- Docility
- Placidity
- Ability to be trained.
What does artifical selection produce?
New breeds or organisms
What are some organisms that humans have selectively bred?
- Cereal
- Rice
- Fruit/ veg
- Cattle
- Sheep
- Pigeons
- Poultry
- Dogs
What characteristics are cereal/ rice/ fruit and veg selectively bred for?
- Increased yeild
- Shorter maturation time
- Resistance to pests
- Infection
- Frost
- Drought
- Flooding and wind
- Impoved flavour
What characteristics are cattle selectively bred for?
- Milk
- Meat
- Leather
What characteristics are sheep and goats selectively bred for?
- Wool
- Meat
What characteristics are horses selectively bred for?
- Haulage and transport
- Racing
- Military use
What characteristics are pigs selectively bred for?
Meat
What characteristics are pegions selectively bred for?
- Flight capacity
- Plumage
What characteristics are poultry selectively bred for?
- Meat
- Feathers
- Eggs
What characteristics are dogs selectively bred for?
- HUnting
- Gaurding
- Racing
- Retreiving
- Companionship
What characteristics are cats selectively bred for?
- Pest control
- Companionship
How long does a selective breeding programme take?
About 20 years
What is the genetic diversity like in selectively bred individuals?
Genetic diversity in the gene pool of the selected breed is reduced.
What is the result of related individuals being bred?
Inbreeding depression
What is the result of inbreeding depression?
The chances of an individual inheriting 2 copies of a harmful reciessive allele are increased.
What is hybrid vigour?
Breeders outcrossing individuals belonging to 2 different varieties, to obtain individuals that are hetrozygous at many gene loci.
What is it called when breeders outcross individuals belonging to 2 different varieties, to obtain individuals that are hetrozygous at many gene loci?
Hybrid vigour
What is a disadvantage to selective breeding?
The organisms genetic diversity is reduced, meaning if a pathogen was intoduced, most plants would succumb to the infection.
How can breeders overcome the problem of selectivley bred species and infections?
Breeders out outcross the cultivated varieties to be more like their wilds ancestors to inceasr hybrid vigiour. Samples of such wild ancestral types need to be conserved, often in seed banks.
What have wheat grown in the UK been artificially bread with?
Much wheat in the Uk has a dwarfing allele introduced from a Japanese variety of wheat.
Why was UK wheat bred With a Japanese variety of wheat to give it a dwarfing allele?
If given extra fertiliser, the wheat does not grow taller and fall over in the wind, but it uses the extra nutrience to increase seed size and yeild.
What is the problem farmers are facing with wheat with the dwarfing allele? How can it be fixed?
If the enviromental temperatures rise above 30°, the effect of this allele is changed and the yeild is decreased. If climate change produce higher temperatures, a new breed of wheat will have to be developed.
What are wheat breeders looking to do to overcome the problem of the dwarfing allele and climate change?
Breeders are looking in a gene bank for different dwarfing alleles.
What do gene banks do?
Gene banks store genomes, but in their organism.
What are some examples of gene banks?
- Rare breed farms
- Wild populations of organisms
- Crops in cultivation
- Botanic gardens and zoos
- Seed banks
- Sperm banks
- Cells in tissue cultures
- Frozen embryos
What are a couple if ethical considerations of artificial selection?
- Domeaticated animals retain many juvenile chcarcteristics making them freindly, but less likely to be able to defemd themselves. The loss of their nervous disposition can also make them easy prey.
- Likestock are selected to make more meat and less fat, so they mighy succumb to low enviromental temperatues during winter if they were not housed.
What is the outcome of humans selectively breeding dogs for thousands of years?
- The traits in dogs, considered desirable by humans, might put the dogs at a selective disadvantage if they had to survive in the wild.
- Some breeds, though interbreeding from a limited number of pedigree dogs, have suscetibilty to disease.
- Some coat colours, selected because humans like the look of them, would also fail to camoflage the animals.
What conditions are boxers susceptable to due to interbredding of limited pedigree dogs?
Cancer and heart disease
What conditions are Labrador retreiver susceptable to due to interbredding of limited pedigree dogs?
- Chronic skin itchiness
- Abnortmality of hip joints and elbow joins
- Shoulder pain and lameness
What conditions are german sheppards susceptable to due to interbredding of limited pedigree dogs?
- Heart disease
- Cancer
- Elbow and hip displasia
- Skin infections
- Lack of digestive enzymes
What conditions are cocker spaniels susceptable to due to interbredding of limited pedigree dogs?
- Inflamation of ear
- Glaucoma (incerased pressure inside the eyes)
What conditions are Bulldogs and Pinkinese susceptable to due to interbredding of limited pedigree dogs?
- Breathing problems
- Hip and albow problems
- Difficulty whelping
What conditions are Dalmations susceptable to due to interbredding of limited pedigree dogs?
- Congenital deafness
- Heart disease
- skin itchiness
- Infections
What conditions are Dobermans susceptable to due to interbredding of limited pedigree dogs?
- Heart failure
- Spinal cord deformity
- Paralysis
What conditions are Great Danes susceptable to due to interbredding of limited pedigree dogs?
- Heart disease
- Bone cancer
- Twisting of the stomach
- Shoulder pain and lameness
- Spinal cord deformity and paralysis
What conditions are West Highland Terriers susceptable to due to interbredding of limited pedigree dogs?
- Dry eye
- Skin irritaion
- Infections
What is codominance?
Where both alleles present in the genotype of a hetrozygous individual contibute to the individual’s phenotype.
What is an example of codominance in animals?
Coat colour in shorthorn cattle. The one gene for coat colour has 2 alleles: C^r (red) and C^w (white).
What colour will the coat of a northen cattle which have homozygous alleles for a red coat? (Codominance)
The cattle would have a red (chestnut) coat.
What colour will the coat of a northen cattle which have homozygous alleles for a white coat? (Codominance)
The cattel will have a white coat
What colour will the coat of a northen cattle which have hetrozygous alleles for a red coat and a white coat (C^rC^w)? (Codominance)
The cattles coat will be both red and white- roan.
What is the MN blood group system controlled by?
A single gene with 2 alleles, G^m and G^n.
What does the gene that controlles the MN blood group code for?
The gene codes for a particular protein on the surface of erythrocytes. The G^m allele codes for one version of the protein and the G^n allele codes for a slightly differrent version of the protein. These alleles are condominent.
What are the alleles for ABO blood groups?
I^A and I^B are codominant to each other. An individual of geneotype I^AI^B expressed both and has both types of isoagglutinogen protein on their eurythrocytes. The inheritace of these blood groups a;sp shows dominance, as both I^A and I^B are dominant ro the allele I^O.
What is sickle cell anaemia caused by?
A mutation in the gene that codes for the B-golbulin chain of haemoglobin.
What is the normal and the mutant allele for sickel cell amaemia represented by?
Hb^S- mutatedc
Hb^N- normal
What is the inheritance pattern for sickel cell anaemia?
It is recessive.
What is allopatric speciation?
The formation of 2 different species from one original species, due to geographical isolation.
Define speciation.
The splitting of a genetically similar population into 2 or more populations that undergo genetic diffrentiation and eventually reproductive isolation, leading to the evolution of 2 or more species.
What is sympatric specification?
Formation of 2 different species from one original species, due to reproductive isolation, while the populations inhabit the same geographical location.
What must happen for a species to evolve into 2 new species?
The species must be split into 2 isolated populations.
If one species have evolved in to 2, what happens if there is a mutation in one of these species?
Any mutation that occurs in one population are not transmitted by interbreeding to the other population.
When a species is split, how does it evolve into 2 different species?
In each loaction, there will be different pressures and each population will accumulate different allele frequencies- each population can evolve along it’s own lines.
What is it called when during evolution of 2 species from one, bu can still interbreed?
Sub-species
How can you tell when 2 species are eveolving from 1, when they are now different species?
They will not be able be interbreed. There would have been sufficient genetic, behavioural and phycological changes.
What is the process where a new species is formed called?
Speciation.
What are the 2 main iolating mechanisms?
- Goegraphic
- Reproductive
How does geographic isolation form 2 species?
Being separated into 2 populations, creates different selection pressures in the 2 different. enviroments, the undogo independent changes to the allele frequencies and/ or arrangments within their gene pools. These genetic changes may be the result of mutation, selection and genetic drift.
What sort of speciation comes from graphical isolation?
Allopatric speciation
What may lead to reproductive isolation of one population to another?
Biological and behavioural changes.
How may changing foraging behaviour cause reproductive isolation?
If a population changes their foraging behaviour and become active at dawn, dusk or at night rather than during the day, it enables them to exploit a new niche, the members of the day population will unlikely to mate with the member active in the night.
How many genetic changes cause reproductive isolation?
- Prevent gamete fusion
- Make zygotesless viable, so they fail to develop
- Lead to infertile hybrid offspring with an odd number of chromosomes, so chromosome pairing during meiosis cannot occur.
What may prevent mating between members of reproductively isolated populations?
Mutations leading to changes in:
* Courtship behaviour (e.g.time of year).
* Animal genitalia or plant structure.
What is speciation resulting from reproductive isolation called?
Sympatric speciation.
What is population genetics an attemot to study?
The variation in the alleles and the genotypes within a gene pool and hiw their frequencies vary over time.
What are some factors the affect allele frequencies within populations and hance the genetic diversity within a gene pool?
- Population size
- Mutation rate
- Migration
- Natural selection
- Changes to enviroment.
- Isolation of a population from other populations of the same species.
- Gene flow
What can 2 populations of the same species not do if they are so genetically different?
They cannot interbreed and form fertile offspring- speciation would have previously occured.
What does the Hardy-Weinburg principle do?
It describes and predicts a balenced equilibrium in the frequencies of alleles and genotype within a breeding population.
Also used to determine the frequencies of those carrying a recessive allele for a genetic disordert with a reciessive inhertance pattern.
What does the Hardy-Weinberg principle assume?
- The population is large enough to make sampling arror negliable.
- Mating within the population occurs at random.
- There is no selective advantage for any genotype and hance no selection.
- There is no mutation, migration or genetic drift.
What are the 2 equations needed for the Hardy-Weinberg principle?
p+q=1
p^2+2pq+q^2=1
What is directional selection?
A trype of natural selection that occurs when an enviromental change favours a new phenotype and so results in a change in the population size.
What is the founder effect?
When a small sample of an original population establishes in a new area; its gene pool is not as diverse as that of the parent population.
What is a genetic bottleneck?
A sharp reduction in size of a population due the enviromental catastophes such as earthquakes or habitat destruction. As population expands, its less diverse than before.
What is stabilising selection?
Natural selection leading to consistancy within a population. Intermediate phenotypes are favoured and extreme phenotypes selected against. Alleles for extreme phenotypes may be removed from the population. Stabalising selection reduces genetic variation within the population.
What introduces new alleles onto a population?
Mutations and migration.
What will happen to allele frequencies within a population over time?
They will change.
What may natural selection maintain and lead tpo?
May maintain consistancy of a species and lead to a new species.
When does stabalising selection occur?
Stabalising selection normally occurs when the organisms’ enviroment remains unchanged.
What phenotypes does stabalising selection favour?
Intermediate phenotypes
What does the graph showing stabalising selection look like?
What is disruptive selection?
Also known as diversifying selection, it favours both extreme phenotypes, and the im=ntermediate phenotype is selected against.
Give an example (with rabbits) of disruprive selection?
In a population of black, white and agouti rabbits, where agouti gives the best camoflage by blending into the background, more of the agouti rabbits would survive to reproduce. If this population moves to an area with black and white riacks, then the black and white rabbits could survive better- eventually this population would undergo diruptive selection.
What does the graph of disruptive selection look like?
What is directional selection?
Over several generations, there is a gradual shift in the optimum value for their offspring.
What is an example of directional selection? (colder temperaures)
If the enviroment gets colder, there may be an advantage to be larger, so a new mass becomes the ideal and will be selected for. If the laregr individuals survive and reproduce, they will be more likely to pass the genes and alleles for larger size to their offspring.
What is directional selection used for?
Its used by plant and animal bredders to produce desirable traits. (Artifical selection)
What does the graph for directional selection look like?
How can genetic drift occur?
- Genetic bottleneck
- Founder effect
What is genetic drift?
When a population decends from a small number of parents coming from a larger population.
What is genetic bottleneck?
When a population size shrinks and then increases again.
What would have happened to the genetic diversity after a population has gone through genetic bottleneck?
The genetic diversity within that population will be reduced.
What may be a concern if after a genetic bottleneck the size of the population shrinks too much?
If the population shrinks to a size too small, its fertility will be affected, leading to the species becoming endangered and then extinct.
How could genetic bottleneck improve the gene pool while shrinking genetic diversty?
Some individuals that survive may have a particular advantage, for example, resistance to a certain pathogen.
What process has a species that has been selectively bred for certain traits been through?
They have been through a genetic bottleneck.
What is the founder effect?
A new population is established by a very small number of individuals who originate from a larger population, the population is likely to exhibit loss of genetic variation.
What is an example of the founder effect?
Some groups of migrating humans, not fully representative of the parent population, have set up populations in new areas. If they remained isolated from other human populations, then the new population will have a small gene pool. The has happened in Ice;and, Easter island and among the Armish people of North America.
What is continous variation?
Variation that produces phenotypic variation where quantitative traits vary by very small amounts between one group to the next.
What is discontinous variation?
Genetic variation producing discrete phenotypes- 2 or more non-overlapping categories.
What is discontinous variation usually determined by?
Usually determined by the allelels of a single gene locus- they are monogenic.
How can the alleles of 2 genes interact to govern a single characteristic in discontinous variation?
- Different alleles at a gene locus have large effects on the phenotype.
- Different gene loci have quite different effects on the characteristic.
By what process is discontinous variation caused when different gene loci interect to influence one characteristic?
Epistasis
What is the characteristic for continous variation?
They are polygenic
In what way does phenotypic categories vary as a result of alleles of a gene contributing to a small amount of the phenotype? Explain what the number of gene loci contributing to this affects?
The pheonotypic categories bvary in a quantitative way. The greater the number of gene loci contributing to the determination of the characteristic, the more continous the variation.
What is quantitative genetics?
The study of the genetics of inhertied characteristics.
Whats the study of the genetics of inhertied characteristics called?
Quantitative genetics
What sort of characteristics does the enviroment have a greater effect on?
The enviroment has a greater effect on the expression of polygenes/ polygenic characteristics than it does on the monogenetic characteristics.
What is the chi-squared test?
A statistical test designed to find out if the difference between observed and expected data is significant or due to chance?
Why would we have to use the chi-squared test?
If we obtain results that are not as quite as expected, we need to know wheter the difference is due to chance or weather the difference between what we observe and what we expect is significant.
What might it mean if by using the chi-squared test, you find the differece between data is significant?
It may be that our inheritance pattern is different to what we thought and we need to rethink our observations.
When can you use the chi-squared test?
When
* The data are in categories and are not continous
* The sample size is large
* We have a strong biological theory to use to predict expected values
* The data are only raw counts- percentages annd ratios cannot be used
* There are no zero scores in the raw count data.
What do statistical tests directly test?
Statistical tests cannot directly test a hypothesis; instead they test a null hypothysis.
What is the null hypothesis for a chi-squared test?
“There is no statistically significant difference between the observed and the expected data. Any difference is due to chance.”
What is the equation for the chi-squared test?
x^2=Σ((O-E)^2/E)
Describe what’s going on in the chi-squared equation?
x^2=((O-E)^2/E)
- The differences may be positive or negative, so they are squared. This prevents and negative values cancelling out positive values.
- Dividing by E takes into account the size of the numbers.
- The “sum of sign” takes into naccount the number of comparisons being made.
What does the number of degrees of freedom equal?
The number of degrees of freedom= number of categories -1
