Inheritance Flashcards
(94 cards)
1
Q
gene
A
A sequence of bases on DNA that code for a protein which results in a characterisitic
2
Q
allele
A
A different version of a gene. Code for different versions of the same characteristic
3
Q
genotype
A
Th genetic composition of an organism
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phenotype
A
Actual appearance of an organism. - the expression of their genetic constitution and interaction with envo
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Dominant
A
An allele who’s characterisitic appears in the phenotype even when there’s only 1 copy.
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Recessive
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An allele who’s characteristic only appears in the phenotype if 2 copies are present.
7
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Codominant
A
Alleles that are both expressed in the phenotype- neither one is recessive
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Q
Locus
A
The fixed position of a gene on a chromosome
9
Q
Homozygous
A
An organism that carries 2 copies of the same allele
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Heterozygous
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An organism that carries 2 different alleles
11
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Carrier
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A person carrying an allele that is not expressed in the phenotype but can be passed on to offspring
12
Q
Multiple alleles
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When a gene has more than 2 alleleic forms
13
Q
Modification
A
Any change to the phenotype by envo effects which are not usually inherited by future generations
14
Q
Genetic crosses
A
Show genotype of parents and potential genotypes of offspring. At the end of the cross state the characteristic followed by the letters which are responsible for this characteristic
15
Q
Codominance
A
Occurs when both alleles are equally dominant so both are expressed in the phenotype. Represented using the same base letter but 2 different subscripts.
e.g. Sickle cell anaemia= Hb has a diff shape
H^N = normal Hb
H^S= Sickle cell Hb
H^N H^N= no sickle cell
H^S H^S= sickle cell
H^N H^S= sickle cell trait= some normal Hb, some sickle Hb
16
Q
Multiple alleles
A
e.g. ABO blood group system in humans have 3 alleles for blood type
I^A= blood group A I^B= blood group B I^O= blood group O
I^A and I^B = codominant
I^O= recessive
17
Q
Dihybrid cross
A
- list all possible alleles from parents
2. cross all the different alleles
18
Q
Phenotypic ratios- monohybrid crosses
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if parents are RR and rr then all offspring= heterozygous= Rr
F2 generation= 3:1 dominant:recessive
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phenotypic ratios- dihybrid crosses
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if parents are RRYY and rryy then all offspring are RrYy
f2 generation: 9:3:3:1
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Codominant
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if parents are H^N H^N and H^S H^S then all offspring heterozygous.
f2 generation 1:2:1 homozygous: heterzygous:homozygous
21
Q
sex linkage
A
The genetic info for gender is carried on 2 sex chromosomes
females= XX males =XY
A characterisitic is sex linked when the allele that codes for it is located on a sex chromosome
22
Q
Y chromosome
A
smaller than X chromosome and carries fewer genes. Most genes on the sex chromosome are only carried by the X chromosome.
23
Q
Why are males more likely to inherit genetic disorders?
A
Males have only 1 X chromosome so have 1 allele for sex linked genes. As they only have 1 copy they express this characteristic even if its recessive.
females need 2 copies of the recessive allele, males only need 1.
affected men can’t pass on condition to sons, can only make daughters carriers
24
Q
Autosome
A
Any chromosome that isn’t a sex chromosome. Autosomal genes= genes located on autosomes
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genes on same autosome
These genes are linked because they're on the same autosome so will stay together during the independent segregation of chromosomes in meiosis 1. Alleles will be passed on to the offspring together
the only reason this wouldn't happen is if crossing over splits them up first.
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Crossing over and genes
- closer together 2 genes on an autosome= more closely to be linked= crossing over less likely to split them up
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Ratio of 2 genes that are autosomally linked
instead of 9:3:3:1 more likely to be ratio of 2 heterozygous monohybrids - 3:1 because the 2 alleles are inherited together
when you do a genetic cross the characteristics with the highst ratios= linked
characteristics with low ratio= due to crossing over= recombinants
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Epistasis
when the allele of one gene masks(blocks) the expression of the allele of other genes
this is because many different genes control the same characteristic - they interact to form the phenotype
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dihybrid cross involving a recessive epistatic allele
- this is when having 2 copies of the recessive epistatic allele masks the expression of the other gene
- crossing a homozygous recessive parent and a homozygous dominant parent will give you a ratio of 9:3:4 in the F2 generation. ratio of dominant both: dominant epistatic, recessive other: recessive epistatic
30
dihybrid cross involving a dominant epistatic allele
- having at least one dominant epistatic allele masks the expression of the other gene
- crossing over homozygous recessive and homozygous dominant will get a ratio of 12:3:1 in F2 generation. dominant epistatic: recessive epistatic: recessive both
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Chi squared test purpose
to see if the results of an experiment support a theory
the theory is used to predict an expected result
the experiment is carried out and an observed result is recorded.
null hypothesis always states that there is no significant difference between the observed and expected results
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conclusions with chi squared
- critical value used to find if there is a significant difference between observed and expected results
- if chi squared value = equal/larger than CV then there is a significant difference, reject null hypothesis, probability is less than 5% that differences in results are due to chance
- if value less than CV then difference is not significant so accept null hypothesis. Greater than 5% probability that differences in results are due to chance
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species
group of similar organisms that can reproduce to give fertile offspring
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population
group of organisms of the same species living in a particular area at a particular time (have potential to interbreed)
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gene pool
the complete range of alleles present in a population
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allele frequency
how often an allele occurs in a population
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hardy weinburg principle
- mathematical model
- predicts that the frequencies of alleles in a population won't change from one generation to the next
- prediction is only true under certain conditions
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conditions for hardy weinburg prediction to be true
1. population is isolated- no flow of alleles in/out of population
2. no mutations taking place
3. There's a large population
4. mating with the population is random- no selective breeding
5. no immigration/emmigration
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p + q = 1
p= frequency of one allele- usually dominant
q= frequency of another allele= usually recessive
1 is the total frequency of all possible alleles for a characteristic in a certain population
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p^2 +2pq +q^2 = 1
```
- used to calculate the frequency of one genotype
p^2= homozygous dominant genotype
2pq= heterozygous genotype
q^2= homozygous recessive
ALWAYS START WITH RECESSIVE
```
41
How does gene mutation cause variation?
error during DNA replication.
| change in the order of base alters the aa sequence in the protein coded for by the gene
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how does independent segregation cause variation?
during meiosis maternal and paternal chromosomes are reshuffled. the chromosomes and alleles of genes can combine in new ways
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how does crossing over cause variation?
during metaphase 1 sections of chromatids in the bivalent are interchanged. blocks of genes are moved and linked alleles may separate and rejoin in new combinations
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how does chromosome muation increase variation?
during cell division sections of chromosome are displaced e.g. during anaphase . this can result in genes being deleted, duplicated or inversion of a sequence.
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how does random fertilisation increase variation?
each parent is genetically different and can produce a huge number of gametes. which gametes fuse at fertilisation is a matter of chance.
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how does environmental cause variation?
the expression of genes may be affected by diet, disease or temperature during development. Mutagens may cause gene mutations in somatic cells.
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habitat
the place where an organism lives
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population
all the organisms of one species in a habitat
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community
populations of different species in a habitat make up a community
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ecosystem
a community and all the non living(abiotic) conditions in the area in which it lives. Ecosytems can be small or large
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abiotic
the non living features of the ecosystem
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biotic
the living features of the ecosystem
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niche
the role of a species within it's habitat e.g. what it eats, where and when it feeds
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adaptation
a feature that members of a species have that increases their chance of survival and reproduction
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the niche of a species involves what type of interactions?
biotic interactions- e.g. what the organisms eats and those it's eaten by
abiotic interactions- e.g. the oxygen an organism breathesin and the carbon dioxide it breathes out.
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properties of a niche
every species has it's own unique niche
if two species try to have the same niche , they will compete with each other.
one species will be more successful than the other until one species is left
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3 different types of adaptation
1. physiological (processes inside the body)
2. Anatomical (structural features of the body)
3. Behavioural(the way an organism acts)
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natural selection in an ecosystem
organisms with better adaptations are more likely to survive , reproduce and pass on the alleles for their adaptations so the adaptations become more common in the population
every species is adapted to use an ecosytsem in a way that no other species can - it has it's own unique niche.
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how are organisms adapted to abiotic factors?
e.g. seals layer of blubber to keep warm in the coldest areas
hibernation over winter to conserve energy
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adaptations to biotic conditions
e.g. sea otters use rocks to smash open clams . increases chance of survival because it gives them access to another source of food.
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define population size
the total number of organisms of one species in a habitat
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carrying capacity
the maximum stable population size of a species that an ecosystem can support.
varies as a result of biotic and abiotic factors
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how is population size affected by abiotic factors
e.g. light,water,space,temperature
| when abiotic conditions are ideal for a species organisms can grow fast and reproduce successfully
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how is population size affected by biotic factors
1. interspecific competition
2. intraspecific competition
3. predation
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interspecific competition
when organisms of different species compete with each other for the same resources .
it can mean that the resources available to both populations are reduced - if they share the same source of food, there will be less available to both of them = less energy for growth and reproduction so the population sizes will be lower for both species
if one species is better adapted to its surooundings, it will outcompete the other species - less adapted species will not be able to exist alongside the better adapted species
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intraspecific competition
competiton within a species
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how does intraspecific competition arise?
1. the population of a species increases when resources are plentiful. As the population increases, there'll be more organisms competing for the same amount of space and food
2. eventually resources such as food and space become limiting- there isn't enough for all the organisms. the population then begins to decline
3. smaller pop= less competition for space and food which is better for growth and reproduction- so pop starts to grow again
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predation
where an organism kills and eat another organism .
| the population sizes of predators and prey are interlinked
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predator-prey cycle
1. as prey population increases, there's more food for predators so the predator population increases
2. As the predator population increases, more prey is eaten so the prey population then begins to fall
3. this means there's less food for the predators so greater competition so their population decreases and so on
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variation
the differences that exist between individuals
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variation within a species
individuals in a population can show a wide range of phenotypes. Having a wide range of phenotypes means that if conditions change some may be able to survive.
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selection pressure
any factor that affects an organism's chance of survival and reproduction
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gene pool
total number of all the alleles of all the genes of all the individuals within a population at a given time
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how does natural selection occur?
1. individuals of the same species vary because they have different alleles.
2. predation,disease and competition (selection pressures) create a struggle for survival
3. as individuals vary some are better adapted to the selection pressures than others.
4. therefore there are differential levels of survival and reproductive success in a population.
5. Individuals with a phenotype that increases their chance of survival are more likely to survive ,reproduce and pass on their genes inc the beneficial allele than individuals with a diff phenotype.
6. greater proportion of next generation inherit the beneficial allele
7. they are more likely to survive,reproduce and pass on their genes
8. frequency of beneficial allele in the gene pool increases.
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why do populations rarely increase exponentially?
death rate is high
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why have some populations evolved high reproduction rates?
to ensure a sufficiently large population survives to breed and produce the next generation. This compensates for high death rates from predation etc.
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why have some populations evolved low reproduction rates?
involves a higher degree of parental care. the lower death rates as a result of this help to maintain population size.
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what is the link between overproduction and natural selection?
leads to intraspecific competition
the individuals in the population that are best adapted are the ones that will survive and breed passing on the beneficial allele. over time the population will have evolved a set of alleles that are better adapted to the envo.
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types of natural selection
1. stabilising
2. directional
3. disruptive
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stabilising selection
when individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
occurs when envo isn't changing
reduces the range of possible phenotypes
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directional selection
where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce.
could be in response to change in envo.
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disruptive selection
when individuals with alleles for for extreme phenotypes at either end of the range are more likely to survive and reproduce.
the opposite of stabilising selection because characteristics towards the middle of the range are lost
occurs when the envo favours more than 1 phenotype.
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speciation
the development of a new species from an existing species
occurs when populations become reproductively isolated- changes in allele frequency cause changes in phenotypes which mean they can no longer interbreed to produce fertile offspring
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allopatric speciation
requires geographical isolation
1. populations that are geographically isolated will experience slightly different conditions e.g. diff climates
2. 2 separate gene pools
3. variation exists within a species due to mutation
4. the populations will experience different selectional pressures so different changes in allele frequency will occur. e.g. diff alleles will be more advantageous in diff conditions
5. this leads to differential reproductive success
6. changes in allele frequency will lead to differences accumulating in the gene pools of the separate populations= changes in phenotypic frequencies
7. over time individuals from the diff populations will have changed so much that they wont be able to breed to produce fertile offspring= 2 separate species
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sympatric speciaation
- no geographical isolation needed to become reproductively isolated
e.g. polyploidy = sometimes mutations occur which increase the number of chromosomes, individuals with diff number of chromosomes can't produce sexually to give fertile offspring
if a polyploidy organism arises in a diploid population- the polypoidy organism will be reproductively isolated
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reproductive isolating mechanisms: ecological
populations inhabit different habitats within the same area so rarely meet
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reproductive isolating mechanisms:temporal
individuals from the same population develop different flowering/mating seasons, become sexually active active at different times of the year.
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reproductive isolating mechanisms: behavioural
group of organisms develop courtship rituals that aren't attractive to the main population
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reproductive isolating mechanisms: mechanical
changes in genitilia prevent successful mating
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reproductive isolating mechanisms: gametic
gametes may be prevented from meeting due to genetic/biochemical incompatibility.
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reproductive isolating mechanisms: hybrid sterility
hybrids formed from the fusion of gametes from diff species are sterile because they cannot produce viable gametes e.g. 63 chromosomes= can't pair up during meiosis.
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genetic drift
this is when chance rather than envo factors dictates which individuals survive, breed and pass on their alleles.
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how does genetic drift occur?
1. individuals within a population show variation in their genotypes
2. by chance the allele for one genotype is passed on to the offspring more often than the others
3. number of individuals with the allele increases
4. changes in allele frequency in 2 isolated populations could eventually lead to reproductive isolation and speciation
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link between natural selection and genetic drift
work alongside each other to drive evolution
evolution by genetic drift has a greater effect on smaller populations where chance has a greater influence
in larger populations any chance variations in allele frequency even out.
