6.2 Flashcards
what is a phenotype
the apperance of a living organism
what is a phenotype influenced by
both its genotype and its environment
What have mutations contributed to
the process of evolution
What is a mutation and what may it involve
it is a change to the genetic material, this may involve changes to the strucutre of DNA or changes to the number or gross strucutre of chromosomes
what may lead to genetic variation
sexual reproduction and mutations
what is a mutagen
a physical or chemical agent that can increase the rate of mutations
What are some examples of mutagens which are physical agents
x-rays, gamma rays, UV lights
What are some examples of mutagens which are chemical agents
benzopyrene (in tobacco smoke), mustard gas, nitrous acid, reactive oxygen species
What are some examples of mutagens which are biological agents
some viruses, transposons (jumping genes, reminents of viral nucelic acid that’s become part of our genome), food contaminants like alcohol or mycotoxins from fungi
What may mutations be
harmful, advantageous or neutral
What are mutations that occur during gamete formation
persistent:they can be transmmitted through many generations without change and random:they are not directed by a need on the part of the organism in which they occur
when do chromosome mutations occur
during meiosis
what are the different types of chromosome mutations
deletion, inversion, translocation, duplication, non-disjunction, aneuploidy, polyploidy
What is deletion in chromosome mutations
part of a chromosome, containing genes and regulatory sequences is lost.
What is inversion in chromosome mutations
a section of a chromosome may break off, turn through 180degress then join again, although all genes still present, some may now be too far away from their regulatory nucelotide sequences to be properly expressed.
What is translocation in chromosome mutations
a piece of 1 chromosome breaks of and becomes attached to another chromosome, this may interfere with the regulation of the genes on the translocated chromosome.
What is duplication in chromosome mutations
a piece of a chromosome may be duplicated, overexpression of genes can be harmful, as too many of certain proteins or gene-regulating nucleic acids may disrupt metabolism
What is non-disjunction in chromosome mutations
1 pair of chromosmes or chromatids fails to separate, leaving 1 gamete with an extra chromosome. When fertilised by a normal haploid gamete, the resulting zygote has 1 extra chromosome. Down-syndrome is caused by non-disjunction.
What is aneuploidy in chromosome mutations
the chromosome number is not an exact multiple of the haploid number for that organism. Sometimes chromosomes or chromatids fail to separate during meiosis.
What is polyploidy in chromosome mutations
if a diploid gamete is fertilised by a haploid gamete, the resulting zygote will be triploid (have 3 sets of chromosomes). The fusion of 2 diploid gametes can make a tetraploid zygote. Many cultivated plants are polyploid (more than 2 sets of chromosomes)
what has genetic variation from sexual reproduction contributed to
evolution
Meiosis produces genetically different gametes, during meiosis what cause this genetic variation
allele suffling (swapping of alleles between non-sister chromatids) during crossing over in prophase 1), 9ndependant assortement of chromosomes in metaphase/anaphase 1 and independent assortment of chromatids in metaphase/anaphase 2
are gametes produced by meiosis individually and genetically similar
no, they are dissimilar
What are gemetes produced by meiosis
individually and geentically dissimilar, they’re haploid, containning 1 of each pair of homologous chromosomes and 1 allele for every gene
what does the random fusion of gametes create
more genetic diversity, any male gamete can combine with any female gamete from an organism of the same species
what does random fertilisation of gametes that are already genetically unique produce
an extensive genetic diversity amoung the offspring
what are some examples of phenotypic variation caused by the environment and not passed through genes
speaking with a regional dialect, a persons offspring doesn’t inherit dialect through their genes, losing a digit or a limb or having a scar following an injury.
what is an example of the environment interacting with genes
if plants kept in dim light after germination or soil has insufficient magnesium, leaves don’t develop enough chlorophyll and are yellow. The plant is then chlorotic, or suffering from chlorosis. The plant can’t photosynthesise. Chlorotic plants have the genotype for making chlorophyll but environmental factors prevent the expression of these genes.
what did mendel publish in 1866
the results of his investigations that would lay the foundation for a branch of biology known as genetics
what did Mendel study
an organism that was easy to grow and, although naturally self-fertilising, was easy to cross-fertilise easily
what did mendel work with
7 characteristics of the pea plant, each characteristic having 2 constrasting traits: stem height, seed shape, seed colour, pod shape, pod colour, flower arrangement, flower colour
what did mendel obtain and keep
true-breeding strains, where the trait had appeared unchanged generation after generation, from local seed merchants. Mendel also kept accurate and quantative records of data obtained which he analysed
what did Mendels simplest experiment involve
only 1 characteristic with 1 pair of contrasting traits, he mated individuals from 2 parent strains, each of which showed a different phenotype. 1 parent was true-breeding for tall stems and the other was true-breeding for short stems. The partents were called P1 (parental generation), all offspring from this cross, the F1 (first filial) generation, were phenotypically identical to 1 parent type. They were all tall
what happened when Mendel allowed members oif the F1 genertaion to self-fertilise
the resulting F2 generation contained some short plants, but there were 3 times as many tall as short plants. 3/4 were tall, 1/4 were short
what happened when mdnd crossed true-breeding plants showing the other 6 phenotypic variations
he obtained similar resukts to his first experiment
in pea plants what is the characteristic of height
it is monogenic, it is governed by 1 gene that has 2 distinc alleles T/t
what happens in pea plants when 1 allele, t, is present in a homozygous individual giving a ohenotype of tt
produces phenotypically short plants
what happens in pea plants when the the other allele, T, is present in homozygous (TT) or heterozygous (Tt) indiviuals
produces phenotypically tall plants
what is the allele T and t in pea plants described as
dominant (it codes for a dominat characteristic) and the t allele is recessive (only visible in phenotype if no dominant allele
What can be visulaised in a punnet square
genotypes and phenotypes resulting from the possible combinations of gametes during a monohybrid cross, showing possible outcomes of monogenic inheritence
how do punnett squares work and what do they predict
all possible gametes are assigned to a row, with those of the female parents in vertical colums and those of the male in the horizontal row. The genotypes of the next generation are predicted by combining the male and female gamete genotypes (a process that represents all possible random fertilisation events. The phenotype of the genotype can also be predicted.
In medels experiment which did all short pea plants have gennotype tt
as hsortness is a recessive characteristic so individuals with that phenotype must have genotype, tt. These are called homozygous recessive
How do we know he tall pea plants in the F1 generation all have the same genotype, Tt
they are all heterozygous, this is decuded from the genotypes of thier true breeding parents (TT and tt) and the genotypes of the gametes (T and t) that must have cobined to produce this generation
In the F2 generation some tall plants had genotype TT and some Tt. What does this mean?
they both have the same phenotype, tall, and it is impossible to tell thier genotype from their apperence
What is the test cross
a simple way to test genotypes devised by mendel
How does the test cross work
the organism exhibiting the dominant phenotype (tall) but unknow genotype (TT or Tt) os crossed with an individual showing the recessive phenotype, so being of homozygous recessive genotype (tt). If any of the offspring jave the recessive phenotype then the dominant phenotype organism is heterozygous, Tt
WhT are dihybrid crosses
Investigations that examine the simultaneous inheritance of 2 characteristics
What did Mendel examine the inheritance of in 1 of his dihybrid crosses
Seed shape and seed colour in pea plants, he crossed true-breeding pea plants with yellow and round seeds with true-breeding pea plants that had green and wrinkled seeds
What we’re all the F1 generations in mebdels dihybrid cross
All hybrids, having the phenotype of yellow and round seeds. Each plant in F1 generation is heterozygous for both genes (seed colour and shape), so yellow and round are both dominant traits
From the results of Mendel dihybrid cross what did he deduce
The alleles of the 2 genes are inherited independently of each other, so each gamete has 1 allele for each gene loci, and, during fertilisation, any 2 of an allele pair can combine with any one of another allele pair
What can we do if we consider the 2 crosses for seed colour and shape as 2 independent monohybrid crosses with the 2 sets of trait inherited independently
We can predict the outcome of allowing the members of the F1 generation to self-fertilise
What are the chances of the seed colour being inherited not influenced by
The chances of the trait for seed shape being inherited
If we assume that seed colour and seed shape are 2 separate monogenic characteristics
For the characteristic of colour:In the F 2 generation we would predict 3/4 would be yellow and 1/4, a ratio 3:1, for the characteristics of shape:we would predict 3/4 round and 1/4 wrinkled, ratio 3:1
What is the equation when 2 independent events occur simultaneously
Product of individual probabilities = combined probability of occurrence
What results did Mendel get from his dihybrid cross
9:3:3:1
What did Mendel unknowingly do when investiGting dihybrid inheritance
Without knowing the process of genes or meiosis, chose 2 characteristics, the genes for which are on different chromosomes
what is the result of a huge number of changes occuring anywhere within a gene over time
many genes have morw than 2 alleles
what does it mean when a gene is said to have multiple alleles
when 3 or more alleles at a specific gene locus are known, however, any individual can only posses 2 alleles, one on each gene locus, in a pair of homologous chromosomes
What is a good example of multiple alleles
inheritance of human ABO blood groups, it also demonstrates both dominance and codomincace of alleles are involved
what is codominance
where both alleles present in genotype of all heterozygous indivdual contribute to indivduals phenotype
What are the 4 blood groups (phenotype - A B AB O) determined by
3 alleles of a single gene on chromsome 9, the gene encodes isoagglutinogen, I, on surface of erythrocytes
What is which blood group you get determined by
alleles are present in the human gene pool are IA, IB, and IO. IA and IB are both dominant to IO which is recessive. IA and IB are codominant. If both IA and IB are presebnt in genotypethey both contribute to the phenotype. Any individual will have only 2 of 3 alleles in their blood type
What are the other 22 chromosomes not sex chromosomes called
Autosomes
WhT is each autosomal pair
Fully homologous - they match for length and contain same genes at same loci
What are the sex chromosomes
XY in males XX in females, X and Y chromosomes are not fully homologous, a small part of 1 matches a small part of the other, so these chromosomes can pair up before meiosis
What is human X chromosome involved in
Has 1000 genes involved in determining many charcateristics or metabolic functions not concerned with sex determination and most have no partner alleles on Y chromosome
If a female has 1 abnormal allele on her X chromoskme how will rhe other chromosme be effected
She will hace a funtioning allele on same gene on Other X chromosome
What hapoens if a male in herits from his mother ab X chromosome woth an abnormal allele for a particular gene
He will suffer from a genetic disease as he wont have a functikning allele for that gene
What are males for X linked genes
Functionslly haploid or hemizygous, they cant be heterozygous or homozygous for X linked genes
What ade sex linked characteristics in humans
Haemophilia A and colour blindness
What is haemophilia A
Unable to clot blood fast enough, injuries may cause bleeding or an internal haemorrage
How does haemophilia occur
1 of the genes on the non-homologous region of the X chromosome codes for a blood-clotting protein called factor 8, mutated form of the allele codes for non functionikg factor 8
How are females carriers for haemophilia A
If female has 1 abnormal allele and a functioning 1 enough factor 8 is produced for her to clot blood normally when required, female is a carrier
What happens when female passes faulty X chromosome to her son
He will have no functioning allele for factor 8 on his Y chromosome, he will sufer from haemophila A
How is colour blindness a sex linked characteristic
1 gene for coding for protein involved in colour vision is on X chromosome but not on Y chromosome, mutated allele of thus gene may reuskt in colour blindness
Who will get coliur blindness
A women with 1 abnormal allele and one functioning womt ve colourblind but male woth abromal allele on X chromosome does have funxrioning one on his Y so will be colour blond
What is colour blindness
A recessive sex linked disorder
What is sex linkage in cats
One of the genes, C, for coat colour in cats is sex linked, its on non homologous region of X chromosome
Why do some cats have more than 1 fur colour
The alleles are codominant, both colours contribute to phenotype
How does cat fur colour work in cats depending on sex
Bith orange and black contribute to phenotype, orange allele only expressed in cells where X chromosome bearing black colour coat allele is inactivated and vice versa, male cats may be either black or ginger but not mix as they only have 1 X chromosome
Why is 1 X chromosome inactivated in females
Females have x2 number of X linked chromosomes expressed as males do, but, a mechansim prevents this disparity, in every female cell nucleus, 1 X chromosome is inactivated. Determination of which chromosome is inacivtaed is random diring embryonic development
what are codominant alleles
when both alleles of a gene in the genotype of a heterozygous individual contribute to that individuaks phenotype, 2 alleles are responsible for 2 distinct and detectable gene products
if phenotype of a heterozygotes different to homozygotes
yes
what is an example of codominance in cow skin colour
a homozygous cattle for red coat, have red coat, a homozygous cattle for white coat, have white coat, heterozygous catlle with genotype for red and white coat will have both a red and white coat
what is an example of codominance inheritance in humans with MN blood gorup
MN blood group system controlled by 1 gene with 2 alleles, GM, GN, both code for a slightly different protein on erythrocytes surface, and these alleles are codominant. Child of a coupple with one parent having blood group M and other N will have blood group MN
how is ABO blood group an example of codominance
A and B are dominant to O, but A and B are codomiannt, making 4 blood groups, A,B, AB, O
how is sickle cell anaemia an example of codominace but also why may some people disput this
in heterozygous person, they will have half normal haemoglobin and half muated haemoglobin (cause sickle cell anaemia), however, in a heterozygous individual can’t have sickle cell anaemia, so muated and normal haemoglobin gene only codomiant if haemogolobin molecule considered to be the phenotype, otherwise its a recessive disorder
what is an example of codominant inheritance in plants
if some flowers and white and some are red and they are crossed together and have red and white spots then they’re codominant. Both aalleles R and W are expressed in the phenotype of the heterozygous
what does the term linked mean
when 2 or more gene loci are on the same chromosome
why can’t linked genes undergo sexual assortement
the chromosome, not the gene, is the unit of transmission during sexual reproduction, so linked genes can’t undergo sexual assortement, they are usually inherited together as a single unit
what is autosomal linkage
where genes are linked by being on the same autosome
what does it mean if linked genes are not affetced by crossing over of non-sister chromatids during phrophase 1 of meiosis
then they are always inherited as 1 unit
what may produce unexpected results within autosomal linkage
recombinant gamete formation when there is crossing over between 2 non-sister chromatids during prophase 1
what causes an increased chance of recombinant ganetes forming
the further apart 2 gene loci are on a chromosome
what is epistasis
in some cases different genes, at different loci, on different chromosmes, interact to effect one phenotypic characteristic. When one gene masks or supresses the expression of another gene its called epistasis
what are the 2 different ways gene inquest with epistasis may wokr
anatgonstically or complementary fashion
as the gene loci aren’t linked when epistasis occurs what does this mean
they assort independantly during gamete formation, epistasis reduces the number of phenotypes produced in F2 generation of dihybrid crosses and therefore reduces genetic variation
what does homozygous presence of recessive allele at first locus prevent (epistasis)
the expression of another allele at a second locus, alleles at first locus are epistatic to those at second locus, why are hypostatic to those at first locus
What is an example of dominant epistasis
feather colour in chicken, there is interaction between 2 gene loci, I/i and C/c. I allele of epistatic gene, I/i, prevents formation of colour, even if 1 C allele is present, individuals carrying at least one dominant allele, I, have white feathers even if they also have 1 dominant allele for coloured feathers
in what terms is epistasis often explained in
terms of genes working to code for 2 enzymes that work in succession, catalysing sequential steps of a metabolic pathway
Whar is discontinuous variation
Ehere phenotype clasees are distinct and discrete, each clearly discernible from the others in a qualitative way
What is an example of discontious variation
Ear lobes, attached or inattacehd
What ate characteristics that exhibit discontinuous variation usually dwtetnibed by
Alleles of a single gene locus, they are monogenic, sometimes alleles of 2 genes interact to govern a songle charactetostic
What 2 things effect discontinous variation
Different alleles at a single gene locus hace large effect on phenotype, different gene loci have wuite different effects on characteristic
What may genes at different loci interact to influence
1 characteristic and produce discontinuous variation, as in epistasis
What is continuous variation
Where genetic variation between individuals, even if theyre related, wothin a population shiws a range with a smooth gradation between many intermediates
What is an example of continous variation
Leaf length in plant, birth mass
How do genes determine continuous variation characteristics
Many genes involved, polygenic
Jow is continuous variation determijed
Alleles of each gene many contribute a small amount to the phenotyoe, so alleles hace an addictive effect on phenotype, so phebotypic categories vary in quantative way, greater number of loci contributing to determinatikn of characteristic, more continuous cariation (greater range)
What is the study of continuous variation called
Quantative genetics
When does genetic analysis of inheritance of contibuous cariation traits become difficult to analyse
As number of gene loci increases above 2 (becomes a trihybrid cross)
What does the environment have a greater effect on, polygebic or monogebtic characteristics
Polygenic
What is example of genes interaction w envuronkejt
Person w gebetic potential for height will bot be talk without right nutrients
What introduce bew alleles into a population
Mutation and migration
What does variation in populations mean
Some bettwr adapted than others to environment due to genotype and phenotype differences, these are more likely to survive and reprodice passkng on advantageous alleles, over time, allele frequencies within populatjon will change (natural selection), may also lwad to new species or maintain consistency in species
What are the 3 tyoes of selection
Stabilising, directional and disruptive selection
What is stablilisong selection
Notnally occurs when organisms environment remains unchanged, favours intermediate phenotypes
Example of stablilisong selection
Babies w birth mass near 3.5kg more likely to sirvive, offspring inherit alleles grom them and wlso have mean birth mass
What is directional selection
If environment chnages, like got colder, larger size would be advantage and ideal for selection, larger individuals survive and reproduce and pass on their alleles for large size, over generatoks gradual shift in optimum value for the trait
What happens if populatoon descends from small number of parents
Gene pool woll lack genetic variation, some alleles resulting from mutation bring no advantage or disadvantage on individual, so no selection pressure acting upon them, but, chance events may drastically influence the allele frequecy
What is example of genetic drift
If small popualtion descend from 2 parents and onlt alleles A and a in it, if earthwuake occured 1 of alleles may disappear from pooualtion, populatipn size will recover but genetic diversity will be low. Allele in questikb didnt disapear due to selection pressure but due to genetic drift
When can genetic drift arise
After genetic bottleneck or due to founder effect
What is a genetic bottleneck
When a popualtipn shrinks and then increases again
What happens as result of genetic bottleneck
Genetic diveristy within popultoon will be reduced, loss of some advantageous alleles of disproportionate frequency of deleterious (harmful) alleles, resucing chance og populatiom LT survival
How could a genetic bottleneck be a good thing
If the ones that survive are those that have a particular advantage, then it could improve gene pool whilst shrinking genetic diversity
What is the founder effect
If a new population is established by a very small numver of individuals who originate form a larger parent popualtion, new popualtion will exhibit loss of genetic variation
What is example of founder effect
Some groups of migrating humans, not fully genetically representative of the parent population, have set up populations in new areas, if they remian isolated from other humans then newer popualtion will have smaller gene pool
When is chi squared usef
If we get results that are not as we expected, we need to know if difference is due to chance or if difference between what we expect and observed is significant, if significant may be inheritance pattern is different to what we thiught
When can we use chi squared
When data is in categories and not continuous, we have strong biological theory to use to predict expected values, sample size is large, data is raw (no percebtage or ratio), have strong biolgical theiry to use to predict expected values
What is the null hypothesis
Statistical tests dont directly test hypothesis the test null hypothesis, if null not supported we accept orignal hypothesis, null states, there is no statistically songicicant difference between observed and expected vakues
Explain chi squared equation
Difference between may be positive or negative so it is swuared, dividng by E takes into account size of numvers, sum of sign takes into account number of conarisons being made
What are the 4 steps of chi squared
1.calculate value of x*2 2.determine degrees of freedom (no categories-1), 3.determine value of P from distribution table, w 0.005 probability 4. Decide if difference is significant at 0.005 probability
what does population genetics attempt to study
changes in allele frequencies within a population, overtime
what mmust happem for a species to succeed and not become extinct
it needs genetic variation between the individuals in its populations, individuals inherit their genomes from their parents and pass some of their genetic material to their offpspring
what does population genetics study
the variation in alleles and genotypes within the gene pool and how their frequency varies overtime
what are factors that affect allele frequencies within populations and genetic diversity within the gene pool
population size, mutation rate, migration, natural selection (stabilising, directional, disruptive), changes in environment, isolation of population from other populations of same species (founder effect), non-random mating, genetic drift, gene flow
when does one species become 2
when 2 populations have become so genetically different that they can no longer interbreed to produce fertile offspring, undergone specification and formed 2 new alleles
what is Hardy-Weinberg principle
a fundamental concept in population genetics, describes and predicts a balanced equilibrium in frequencies of alleles and genotype within a breeding population, also used to determine frequencies of those determining a recessive allele (heterozygotes) for a genetic disorder with recessive inheritance pattern, if we know incidence of effected babies born each year in that population
what does Hardy-Weinberg principle assume (4)
population size is large enough to make samoling error negilgible, mating within population occurs at random, no selective advanatge for any genotype and hence no selection, there is no mutation, migration or genetic drift
what must happen for a species to split into 2 separate ones
it must split into an isolated population, as when this happens any mutations that occur in one population are not transmitted by interbreeding to other population. In each location there’s a different selection pressure and each population will accumulte different allele frequencies, so each population evolves differently
what are sub-species
during the evolutionary process when 2 populations are different but can still successfully interbreed
when do 2 populations become separate species
when sufficient genetic, behavioural and physiological changes in 2 populations that they can no longer interbreed
what is specification
the process by which new species are formed
what are 2 main isolating mechanisms
geograophical and reproductive
what is geographical isolation
if populations separated and isolated from each other by geographical features like lakes, rivers, oceans, these act as barrier to gene flow between populations
what is allopatric specification in geographical isolation
isolated populations subject to different selection pressures in 2 different environments, then undergo independant changes to allele frequencies and/or chromosome arrangements in their gene pool, these changes will result in mutation, selection and genetic drift and as a result each becomes adapted to their environment (allopatric selection)
what is reproductive isolation
biological and behavioural changes within a species may cause reproductive isolation
example of reproductive isolation
if mutation leads to some organisms in population changing foraging behaviour and becoming active at dawn, dusk or night rather than day, enabling to exploit new things, members of diurnal population won’t mate with members from crepuscular (active dawn and dusk) or nocturnal population
how may genetic chnages cause reproductive isolation
change in chromosome number may prevent gamete fusion, make zygote less viable so fail to develop, lead to infertile hybrid offspring with an odd number of chromosomes so no chromosome pairing in meiosis
how may mating between members of reproductively isolated population be prevented
by mutations leading to changes in courtship behavour (time of years it occurs or courtship rituals),, antimal genitalia or plant structure
what is sympatric specification
specification resulting from reproductive isolation
difference between artifical and natural selection
natural is having the environment as selection agent, artifical is huamns as agents of selection, breeders select individuals with desired triats and interbreed them and prevent those without desired traits from breeding
what are desirable characteristics in plants
increased yield, pest and disease resistance
what are desirable characteristics in livestock
docility, placidity, ability to be trained (e.g. to accept human as leader)
what are some examples of artifical selection and how there used by humans
cattle (milk, meat), horses (transport), dogs (companionship, hunting), sheep (wool), ceral (improved flavour + dough, pest, flood, wind resistance)
how may new breeds be produced by selective breeding programmes
breeders may grow plant of certain type under conditions they wosh this plant to survive (like low temp), they then select individuals who grow best under these conditions and cross polinate them, collect and sow the seeds and repeat for many generations (up to 20years)
what is interbreeding depression
at each stage of selective breeding ones with most desirable characterostics are chosen and causes reduction in gene pool/genetic diversity. Interbreeding depression is when 2 related individuals aare crossed which results in increased chance of inheriting 2 copies of a harmful recessive allele
what is hybrid vigour
breeders sometinmes outcross individuaks belonging to 2 different varieties to obtain individuals that are heterozygous at many gene loci
why does hybrid vigour need to be increased in commercial plants
as they are all geentically similar and if a pathogen is introduced it could kill them all, some may need to be outcrossed with wild ancestors, often kept in gene bank, in order to retain their genetic diversity
what is purpose of gene banks, give example
purpose is to store genomes, in their organisms. E.g. if a wheat yeild decrease over 30degrees but global warming makes this temp more common may use a gene bank to cross this wheat to create a crop to withstand higher temps
what are examples of gene banks (8)
rare breed farms, wild populations of organisms, crops in cultivations, botanic gardens and zoos, seed banks, sperm banks, cells in tissue culture, frozen embryos
what are ethical consideratioins to artifical selection
domesticated animals retain docile traits making them easy pray/can’t defend themseleves, livestock need less fat and more meet but they may become cold in low temp if not housed, dogs domesticated meaning at disadvantage if they went into the wild, interbreeding caused suseptibiltiy to disease in some dogs, soem coat colours selcted would fail to camoflage animal
give an example of a condition a boxer and german shepard suceptible to
heart diease and cancer
