SECTION 7 - BIO Flashcards
1
Q
Define genotype?
A
the alleles present in a cell (sylabus: the genetic constitution of an organism
2
Q
define phenotype
A
the observable characteristics due to alleles being expressed (sylabus: the phenotype is the expression of this genetic constitution and its interaction with the environment)
3
Q
define locus
A
position of a gene on a chromosome
4
Q
chromatid
A
when DNA in a chromosome replicates the 2 copies are held together by a centromere and are called chromatids.
5
Q
Co-dominant
A
Both alleles are expressed in the phenotype if they are both present. they both produce functional, but diff, proteins. (neither one is recessive)
6
Q
alleles
A
different forms of the same gene
7
Q
dominant
A
allele expressed even if heterozygous. produces a function protein
8
Q
recessive
A
allele expressed only if homozygous. caused by a mutation resulting in the allele producing a non-functional protein.
9
Q
Homologous pair
A
pair of chromosomes in a diploid cell. contain same genes but possibly different alleles. form bivalents during meiosis.
10
Q
monohybrid inheritance
A
inheritance involving a single gene with more than 1 allele
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11
Q
dihybrid inheritance
A
inheritance involving 2 genes at different loci on different chromosomes.
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12
Q
CODOMINANCE.
A
both alleles will be expressed in the phenotype
neither is recessive
there are 3 possible phenotypes:
1) homozygous of one allele
2) homozygous of the other allele
3) heterozygous (has both dominat alellesl)
eg, R=red fur
W = white fur
RR = red fur
WW = white fur
RW= pink fur
13
Q
some genes have more than 2 what? which can lead to what? and give an example?
A
alleles, leading to the expression of many diff proteins in the phenptype. example: Blood type.
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14
Q
MULTIPLE ALLELES
A
GENES HAVING MORE THAN 2 ALLELES.
15
Q
SEX-LINKAGE
A
A GENE THAT IS FOUND ON A SEX CHROMOSOME is said to be ‘sex-linked’
16
Q
most genes on sex chromosomes are carried by which chromosome? and why?
A
most genes on sex chromosomes are carried by the X chromosome. because males only have one X chromosome, they often only have 1 allele for sex-linked genes, because they only have 1 copy of the gene, hence they express the characterisitc of this allele, even if its recessive which means males are much more likely to show recessive phenotypes for sex-linked genes.
17
Q
the gene which determines if you have haemophilia is found on which chromosome, making the disease ____
A
X chromosome, making haemophilia sex-linked
18
Q
haemohpilia is caused by which allele
A
the recessive allele
19
Q
for the recessive haemophilia allele to be expressed, males require how many copies of it and why?
A
1, because males only have 1 x chromosome
20
Q
CARRIER =….
A
some1 who has the faulty recessive allele but is heterozygous with a dominant allele present.
21
Q
explain why males are much more likely to show recessive phenotypes for sex-linked genes? (refer to bothmales and femaels
A
females may be carriers
males require only 1 allele
22
Q
what are autosomal genes?
A
genes that arent found on sex chromosomes
23
Q
autosome
A
any chromosome that is not a sex chromosome (humans have 22 pairs of autosomes, and 1 pair of sex chromosomes)
24
Q
genes on the same autosoome are said to be what?
A
linked
25
genes on the same autosome are said to be 'linked'. they will stay on the same chromosome during which process in meiosis 1, and offspring will inherit what.
Except for which scenario will these 'linked' autosomal genes not stay on the same chromosome, and hence offspring wont inherit the alleles together?
during independent segregation in meisosis, and offspring wil inherit these alleles together.
except for if they are separated during crossing over. (Linked autosomal genes will stay together on the same chromosome — except if they are separated during crossing over, hence The offspring might not inherit those alleles together anymore.) - (leading to a new combo of alleles in the offspring)
26
the closer together the 2 linked genes are on the same chromosome (the closer the autosomal genes are on the same chromosome), the what?
the less likely theyll be split by crossing over.
27
when 2 genes are linked (i.e close together on the same chromosome/autosome), are they separated or not, and what does this lead to in terms of the combonation of alleles prodcued?
they are not separated, hence you would get the same combo of alleles
28
linked genes
linked genes are genes that are close together on the same chromosome (i.e autosome)
29
(linking to flash 27), if 2 autosomes are linked, whats the outcome in terms of phenotypic ratio? (compared with the offspring of a normal dihybrid cross)
u wont get the phenotypic ratio you'd expect from the offspring of a normal dihybrid cross
30
what ratio do u get of the combo of allels in the offspring of a dihybrid cross where both parents are heterozygous.
9:3:3:1 ratio
31
ON THE CONTRAST OF FLASHY 30, WHATS THE RATIO U WOULD GET WITH AUTOSOMAL LINKAGE
3:1, BECAUSE THE 2 LINKED ALLELES ARE INHERITED TOGETHER. (as no separation cuz no crossing over)
32
AUTOSOMAL LINKGAE MEANS WHAT IN TERMS OF OFFSPRING HAVING THEIR PARENTS GENO AND PHENOTYPE.
autosomal linkage means a higher proportion of offspring will have their parents genotype and phenotype
33
define epistasis. how it works and give an eg,
the effect of one gene on another. the 2 genes interact so that one may be masked (prevented from being expressed) by another.
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34
why can epistasis provide difficulties for genetic investigations?
because if the effect of one locus is altered/masked by effects at another locus, power to detect the first locus is reduced.
35
what is the chi-squared (X^2) test used for in the case of genetics and to observe/see what?
to compare the goodness of fit of observed phenotypic ratios with expected ratios.
hence that means we could use it to see if there is a dihybrid cross with no linkage or whetehr the genes involved are linked.
36
in chi squared test in the case of genetics, why will you rarely get the expected phenotypic ratios?
random fertilisation of gametes
epistasis
small sample size
37
to see if the diff between the observed and expected outcomes is significant (i.e are other factors at play) we can use a chi-squared test. explain the whole test and outcome.
1) Find χ² (given in exam)
2) then compare χ² with the critical value (to find the critical value we need to know the degrees of freedom (which is the number of classes - 1), as we use the degrees of freedom to look up the critical value)
3) if the value of χ² exceeds or is equal to the critical value, the null hypothesis is rejected.
(in the example of phenotypic ratios the null hypothesis is that there is no significant difference between the expected and observed phenotypic ratios)
if we reject the null hypothesis this means that: there is less than 5% probability that the diff between the expected and observed phenotypic ratios is due to chance.(final outcome/statement that must be said in exam Q,)
38
species exist as how many populations?
one or more populations
39
define a population
a group of organisms of the same species occupying a particular species at a particular time that can potentially interbreed.
40
GENE POOL
THE COMPLETE RANGE OF ALLELES PRESENT IN A POPULATION
41
ALLELE FREQUENCY (GIVEN AS DECIMAL/%)
HOW OFTEN AN ALLELE OCCURS IN A POPULATION
42
the hardy-weinberg principle provides a mathematical model which predicts what?
that allele frequencies will not change from gen to gen.
43
give the 2 equations for the hardy weinberg principle
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44
what is the HW equation used for
to see whether the frequency of alleles within a population is changing (i.e is there a selection pressure acting on the population and is evolution occuring). this is because by the H-W equation we can calculate the frequency of each allele in a population.
45
as we know the HW principle predicts allele frequencies will not change from gen to gen. this only assumes the following criteria are met (which is not the case in real life). give the following criteria assumed to be met:
No natural selection takes place, meaning all genotypes give indiviudals an equal chance of surving and reproducing
No gene Flow (i.e no immigration/emigration), hence this could introduce new genes or alter existing gene frequencies in the population.
large population sample size (as in a small population, genetic drift (change in allele frequency in a pop due to random chance) has a very large impact cuz each individual makes up a greater proportion of the population)
No mutations occur, so no new alleles are created
46
Define disruptive selecton and give an eg including the graph
where individuals with alleles for characteristics of both extremes at either end of the range are more likely to survive and reproduce.
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47
define evolution
change in allele frequencies in a population
48
define speciation
when new species develop from a common ancestor.
49
how does speciation happen (process)?
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50
allopatric speciation
when species become separated via physical reproductive isolation (eg via a river, or mountain range)
51
sympatric speciation
when populations dont become phyically separated but theres some other reason for reproductive isolation. the reason maybe: Behavioural, Temporal or mechanical (eg, change in the genitcal structure, meaning reproduction is no longer possible between the 2 species)
52
evolution can occur by what 2
Natural selection
genetic drift
53
Genetic drift
when allele frequencies change due to random chance
54
why does genetic drift happen
not every indiviudal will become a parent
not every individual will have the same number of offspring
55
random chance, rather than selection pressures dictates what?
which individuals survive, repodruce and pass on their alleles
56
why does genetic drift have a greater impact on smaller populations
cuz each individual makes up a greater proportion of the population.
57
in a smaller population there is a greater chance that one individual is the sole owner of one allele. if this individual were to die out, what effect does this have on the pop (compared with many more members of the pop sharing the same allele)
this has a much greater effect on the population than if many more members of the population shared this same allele.
58
natural selection and genetic drift work alongisde each other to cause evolution, but one may drive evolution more, depending on what?
size of population
59
does genetic drift cause species to become better adapted to the environment (like natural selection)
NO
60
define a community
populations of different species in a habitat
61
ecosystem
a community and the non-living components of its environment
62
define a niche
a niche is a species role within an ecosystem. this is goverened by its adaptation to both biotic and abiotic conditions. only 1 species can occupy a niche at a given time.
63
if 2 species try occupy the same niche, what wil happen
they will compete with each other.
64
if there is less competion that =
broader niches
65
ABIOTIC VS BIOTIC
ABIOTIC - NON LIVING FEATURES ON AN ECOSYSTEM
bIOTIC - LIVING FEATURES OF AN ECOSYSTEM
66
DEFINE CARRYING CAPACITY
THE MAX STABLE POPULATION SIZE OF A SPECIES THAT AN ECOSYSTEM CAN SUPPORT
67
THE CARRYING CAPACITY DEPENDS ON WHAT
EFFECT OF ABIOTIC FACTORS, LIKE light intensity, water availability, food availability, soil ph , and temp. if conditions are favourable this increases the chances of survival and reproduction, hence increasing the carrying capacity.
The carrying capacity also depends on interactions between organisms, hence including inter and intraspecific competition
PREDATION (when one organism eats another)
68
INTER VS INTRA SPECIFIC COMPETITION
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69
PREDATION FACTOR ON CARRYING CAPACITY AND ITS GRAPH
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70
HOW CAN u estimate a population size of non-motile/slow moving organisms? (give the techniques and explain the procedure)
a) use randomly placed quadrats (random to avoid bias)
1) use a random number generator to generate coordinates and plot the coordinates
2) place quadrat (1m x 1m)
3) count the number of indivudals
4) repeat many times
5) calc a mean (by adding total number of individuals counted and divide by n.o. of samples taken
6) multiply mean by total area
b) use of quadrats along a belt transect - (used to measure gradual changes in pop size across an area)
done by:
taking samples at regular intervals along a transect
71
the more samples you take , the more what
the more reliable the average, as it will reduce the effect of outliers. will also allow u to identify outliers.
72
how can u estimate population sizes of motile organisms? (give the technique and producdure)
method - Mark - release- recapture method
1) capture a sample of indviduals from the population (eg, use pitfall traps for insects)
2) count the number of indivuals (s1) and mark them in a harmless way
3) then release them and allow time for them to distribute evenly amongst the rest of the population
4) capture a second sample from the population
5) count the number of individuals caught (s2) as well as those marked (R)
6)calc population estimate using...
pop size = (s1* S2) / R
where s1 = no. individuals caught in the 1st sample
s2 = no. individuals caught in the 2nd sample
R = number marked in 2nd sample
73
for the mark-release-recapture method, we assume the following criteria are met:
we assume:
marking doesnt affect survival (eg, may make them more visible to predators)
marked individuals mix randomly and evenly with the population
no change in pop size ( due to factors like births, deaths, immi or emigration)
marking is not lost
74
where does primary succession occur
on land that has newly formed/exposed (eg, cooled lava, exposed rocks after a drop in sea level)
75
pioner species live where? (name some of da conditions), and give their adaptations which allow them to live in such conditions.
in areas which have extreme abiotic conditions (hostile), where:
little nutrients are available
unstable substrate
little water is availablle
land is exposed
adaptations:
ability to reproduce asexually (dont need to be pollinated)
ability to fix n2 (gas)
tolerant to salt
ability to rapidly germinate (seeds may be blown/washeed away)
76
why and how do pioneer species change the environment?
to make abiotic conditions less hostile.
HOW?
they erode the rock and this releases minerals
add more humus
when they die and decompose, they increase NO3- content (nitrate)
the new species then may change the environment, so it becomes less suitable for the previous species. conditions become less hostile
77
as a result of pioneer species causing conditions to become less hsotile by changing the env, succession continues and hence different organisms that are better adapted to the improved conditions do what?
outcompete those already there and dominate the ecosystem, more species mov in as a result, increasing the biodiversity.
78
climax comunity
largest and most complex community
79
why are mammals and bird only found in later stages of succession
cuz biomass of plants are not great enough to provide sufficent food. they also need shelter and protection
80
which which species make up to the climax community depends on what?
the climate
81
features of a climax community include ....
same species is present over a long period of time
stable community and stable population
abiotic factors are constant.
82
when is the highest biodiversity reached?
before the climax community
83
what occurs during secondary succession?
the climax community is cleared in some way (eg, forest fire, agricultural purposes..)
succession restarts, but is much quiker as theres already soil present which contains seeds and nutrients (unlike in primary succession) to start a new community. the pioneer species here are larger plants. hence the climax community is reached much faster as your not starting with extreme hot conditions.
84
conservation of habitats frequently involves managing.....
succession
85
why do u prevent succession from continuoing?
to preserve an ecosystem in its current stage of succession. because if another species arrived and dominated, existing species would be outcompeted and die out.
86
WHAT ARE WAYS TO CONSERVE
GRAZING/MOWING - this removes growing tips from plants such as tree saplings or small shrubs, hence these plants are prevented from developing, and hence no climax community is reached.
MANAGED FIRES - all species are wiped out and secondary succession will occur. small species are pioneer species and grow more quickly than larger trees/shrubs
87
at each stage in succession, certain species may be recognised which does what to the env
which change the env so that it becomes more suitable for others species with diff adaptations. the new species may change the env in such a way that it becomes less suitable for the previous species.
88
changes that organisms produce in their abiotic env can result in what?
a less hostile env and change biodiversity.
89
define primary succession?
Primary succession is the colonisation of land by pioneer species that has never previously supported a community — there is no soil or organic material initially
90
Describe how primary succession leads to the formation of a climax community. (4 marks) chatgbt answer bare that in mind
Pioneer species colonise a hostile environment with no soil (e.g. bare rock).
These species break down the rock and die, forming soil and humus, which allows other species to grow.
Over time, the environment becomes less hostile, allowing more complex plants (like grasses, then shrubs, then trees) to replace earlier species.
This continues until a stable climax community forms, where biodiversity and species composition remain relatively constant.
91
secondary succession
Secondary succession is the re-colonisation of an area where a community has previously existed but was removed — soil is already present.
where it happens:
After a forest fire
Following flooding
Land that has been abandoned after agriculture
Storms, deforestation, or land clearance
92
Describe the process of secondary succession in an ecosystem following a disturbance such as fire or deforestation. (4 marks)
Soil is already present, so pioneer species like grasses and fast-growing plants quickly colonise the area.
These species change the abiotic conditions (e.g. increase shade, improve soil nutrients), making the environment more suitable for other species.
Over time, these early species are outcompeted and replaced by shrubs, then trees as succession continues.
Eventually, a climax community is established, with greater biodiversity and stability.
93
key diff between primary and secondary succession
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