Topic 7 Last Flashcards
(48 cards)
1
Q
Geneotype vs Phenotype
A
- Genotype is the genetic constitution of an organism
- Phenotype is the expression of this genetic constitution and its interaction with the environment.
2
Q
What are alleles?
A
- Different forms of the same gene
3
Q
Dominant, recessive, co-dominant
A
- Dominant allele needs one allele present to be expressed in the phenotype
- Recessive alleles need 2 copies present to appear in the phenotype
- Co-dominant alleles are alleles that are both expressed in the phenotype.
4
Q
What is monohybrid inheritance
A
- Inheritance of one single character, controlled by a single gene.
5
Q
What is dihybrid inheritance?
A
- Inheritance of 2 characteristics, controlled by 2 genes
- Involves 2 genes on 2 different chromosomes
6
Q
What is codominance
A
- Both alleles will be expressed in the phenotype
7
Q
What are the 3 possible phenotypes in codominance
A
1) Heterozygous of both alleles
2) Homozygous of one allele
3) Homozygous of another allele
8
Q
What are multiple alleles?
A
- Where some genes have more than 2 alleles, for example bloody type, where type a and b are codominant over allele iO.
9
Q
What is sex-linkage and what impact do Male’s XY have?
A
- A gene that is found on a sex chromosome is said to be ‘sex-linked’
- Most genes on sex chromosomes are carried by the X chromosome so males are much more likely to show recessive phenotypes for sex linked genes as they only have one X chromsome .
10
Q
Why are females said to be carriers of recessive genes?
A
- Their dominant allele on their X chromsome may cancel out the recessive allele on the Y chromosome.
11
Q
What is autosomal linkage?
A
- Autosomal Genes that aren’t found on sex chromosomes.
- Genes found on the same autosome are said to be ‘linked’
- They will stay on the same chromosome during independent segregation in meiosis 1 and offspring will inherit these alleles together.
- The more closely two genes are together on the same chromosome, the less liekly they’ll be split by crossing over.
12
Q
Why is there a 3:1 ratio during autosomal linkage?
A
- Because the 2 linked alleles are inherited together.
13
Q
What is epistasis?
A
- The effect of one gene upon another.
- 2 genes interact, so that one may be masked (prevented from being expressed) by another.
14
Q
Why does epistasis make it difficult for genetic investigations?
A
- If the effect of one locus is altered by the effect at another locus, power to detect the first locus is reduced.
15
Q
What is chi-squared used for?
A
- Used to compare the goodness of fit of observed phenotypic ratios with expected ratios
- Can use to see if there is a dihybrid cross with linkage or no linkage
16
Q
Why is it rare to get exactly the expected phenotypic ratios?
A
- Random fertilisation of gametes
- Epistasis
- Small sample size
17
Q
What is a population?
A
- A group of organisms of the same species occupying a particular space at a particular time that can interbreed.
18
Q
What is the gene pool?
A
- The complete range of alleles present in a population.
19
Q
What is the allele frequency?
A
- How often an allele occurs in a population.
20
Q
What is the prediction of Hardy Weinberg?
A
- Mathematical model which predicts that allele frequencies will not change from generation to generation.
21
Q
Equations of Hardy Weinberg?
A
P+Q=1 (allele frequencies)
p^2+2pq+q^2=1 (frequency of individuals)
P - frequency of dominant alleles
Q - frequency of recessive alleles
2pq - Homozygous
22
Q
What is Hardy Weinberg used for?
A
- To see whether the frequency of alleles is changing (if there is a selection pressure)
- We know this as we can measure the frequency of individuals in a population
23
Q
Assumptions by the Hardy Weinberg
A
1) No natural selection meaning equal chance of survival and reproduction
2) Assumes there is no gene flow, introducing new genes or altering existing genes.
3) Assumes the population is large and isn’t affected by genetic drift
4) Assumes that there are no mutations as allele frequencies don’t get altered.
24
Q
What is disruptive selection?
A
- When two extreme genotypes at both ends of the range are the most common and likely to survive and reproduce.
25
What is evolution?
- The change in allele frequencies in a population
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What is speciation
- When new species develop from a common ancestor
27
Process of speciation
1) Geographic isolation by a natural barrier so reproductively isolated
2) Each population finds itself in a different environment, so experiences different selection pressures
3) Natural selection occurs and different alleles are of an advantage in the different populations.
4) Allele frequencies change in the two gene pools
5) Two populations are so genetically different that they no longer interbreed to produce fertile offspring.
28
Allopatric speciation vs Sympatric speciation
Allopatric - physical reproductive isolation via a river or moutanin range
Sympatric - Populations don't become physically separated but there are other reasons for reproductive isolation.
(change in genetics, behavioural changes)
29
Genetic drift
- When allele frequencies change due to chance
- Not every individual will become a parent
- Not the same offsprint when they do have kids.
(as a result, chance rather than selection pressures dictates the likelihood of reproduction)
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Why does genetic drift have more of an impact in smaller populations?
- Because more individuals make up a larger proportion of the population.
31
Relationship between natural selection and genetic drift?
- Work alongside each other in evolution but ultimately one may drive evolution more, depending on the size of the population.
- Unlike natural selection, genetic drift doesn't cause better adaptation to the environment.
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Community
- Populations of different species in a habitat
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Ecosystem def
- Community and the non-living components of its environment
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What is a niche?
- A species' role within an ecosystem
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What happens when 2 species try to compete for the same niche?
- They will compete with each other.
36
What is the carrying capacity?
- The maximum stable population size of a species that an ecosystem can support.
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Factors which affect the carrying capacity...
- The effect of abiotic factors such as light intensity, water availability, food availability, soil pH and temperature
- Interactions between organisms such as inter and intraspecific competition
- Predation
38
Interspecific vs intraspecific competition
- Interspecific competition is when organisms of different species compete for resources.
- Interspecific competition results in decreasing food availability for both species
- So population size decreases as survival and reproduction is less likely.
Intraspecific competition is when organisms of the same species compete with each other for resources
39
How does predation affect carrying capacity
- Happens when one organism eats another.
- As population size increase, predator population increases but as predators eat prey, their population will also decrease when food becomes scarce.
40
How do we estimate population sizes using radnomly placed quadrats and on what type of organism?
Measure on slow moving organisms
1) Randomly place quadrats, being random to avoid bias.
2) Plot coordinates and use a radnom number generator to generate coordinates.
3) Place a 1mx1m quadrat and count the number of individuals, repeating many times.
4) Calculate the mean
5) Multiple mean x area.
41
Why do we use quadrats?
- To measure gradual changes in population size across an area.
- By taking samples at regular intervals along a transect.
- More samples means more reliability.
42
How do you estimate population sizes for mobile organisms.
- Mark-release-recapture
1) Capture a sample of individuals from the population by using E.g pitfall traps for insects.
2) Count the number of individuals and mark them in a harmless way
3) Return them to mix with the population
4) Capture second sample and count the number of individuals caught and number of those marked.
5) S1 x S2 divided by the number marked in S2
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Assumptions from mark-capture-release
- Marking doesn't affect survival by making them more visible to predators.
- We also assume that marked individuals mix randomly and evenly with the population.
- We assume no change in population size
44
Outline primary succession
- Takes place on land that is newly formed or has been exposed
1) Pioneer species are those that live in extreme abiotic conditions that are hostile with little nutrients or water.
2) Adaptations allow them to live in these conditions such as asexual reproduction.
Or the ability to fix nitrogen and tolerant to salt.
3) Pioneer species change the environemnt to make abiotic conditions less hostile such as eroding the rock and releasing minerals or adding more humus.
4) New species makes the environment more hostile for the previous species.
5) Over time conditions become less hostile and organisms becoming better adapted and outcompete older species.
6) Climax community is formed meaning the same species is stable and has been present over a long period of time.
45
Outline secondary succession
1) Climax community is cleared in some way
2) Succession occurs quicker due to soil that contains seeds and nutrients to start a new community.
3) Pioneer species are larger plants therefore climax community reaches much quicker due to the lack of hostile conditions.
46
Why would we prevent succession from continuing through conservation?
- We prevent succession from continuing to preserve an ecosystem in its current stage of succession.
- If another species arrived and dominated, existing species would be outcompeted and die out.
47
Methods of conservation
- Grazing and mowing to remove growing tips so no climax community is reached.
- Managed fires so all species are wiped out and secondary succession will occur. Small species are pioneer species and grow more quickly than larger trees and shrubs.
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