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Biology AQA > Genetics, Populations, Evolution and Ecosystems > Flashcards

Genetics, Populations, Evolution and Ecosystems Flashcards

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1
Q

define habitat

A

the place where an organism lives

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2
Q

define population

A

all the organisms of one species in a habitat

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3
Q

define community

A

populations of different species in a habitat make up a community

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4
Q

define ecosystem

A

a community, plus all the non-living conditions in the area in which it lives. ecosystems can be small or large

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5
Q

define abiotic conditions

A

the non-living features of the ecosystem, e.g temperature and availability of water

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6
Q

define biotic conditions

A

the living features of the ecosystem, e.g the presence of predators or food

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7
Q

define niche

A

the role of a species within its habitat, e.g what it eats, where and when it feeds

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8
Q

define adaptation

A

a feature that members of a species have that increases their chance of survival and reproduction

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9
Q

explain a niche a species occupies in its habitat

A

its biotic interactions- e.g the organism it eats, and those its eaten by
its abiotic interactions- e.g the oxygen an organism breathes in, and the carbon dioxide it breathes out.

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10
Q

does every species have the same niche?

A

no, every species has its own niche

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11
Q

what types of adaptations are there?

A

physiological; processes inside their body
behavioural; the way an organism acts
anatomical; structural features of their body

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12
Q

what are the benefits of an organism having better adaptations?

A

they are more likely to survive, reproduce and pass on the alleles for their adaptations, so the adaptations become more common in the population.

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13
Q

what are organisms adapted to?

A

both the abiotic conditions (e.g how much water is available) and the biotic conditions (e.g what predators there are) in their ecosystem.

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14
Q

describe an example of when hedgehogs have adapted to abiotic conditions

A

hedgehogs hibernate. and so they are able to lower their rate of metabolism (all the chemical reactions taking place in their body) over winter. this increases their chance of survival because they can conserve energy during the coldest months.

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15
Q

describe an example of when male frogs have adapted to biotic conditions

A

male frogs produce mating calls to attract females. this makes sure they attract a mate of the same species. this increases their chance of reproduction by making successful mating more likely.

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16
Q

what 2 factors causes population size to vary?

A

abiotic factors
biotic factors

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17
Q

define carrying capacity

A

the maximum stable population size of a species that an ecosystem can support.

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18
Q

what do abiotic factors include?

A

abiotic factors include the amount of light, water or space available, the temperature of the surroundings or the chemical composition of surroundings.

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19
Q

how do abiotic factors affect population size (include an example regarding temperature)

A

when abiotic conditions are ideal for a species, organisms can grow fast and reproduce successfully.
e.g when the temperature of a mammal’s surroundings is the ideal temperature for metabolic reactions to take place, they don’t have to use as much energy maintaining their body temperature. this means more energy can be used for growth and reproduction, so their population size will increase.

when abiotic conditions aren’t ideal for a species, organisms can’t grow as fast or reproduce successfully.
e.g when the temperature of a mammal’s surroundings is significantly lower or higher than their optimum body temperature, they have to use a lot of energy to maintain the right body temperature. this means less energy will be available for growth and reproduction, so their population size will decrease.

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20
Q

how do biotic factors affect population size

A

interspecific competition
intraspecific competition
predation

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21
Q

define and explain interspecific competition

A
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22
Q

define gene

A

a sequences of bases on a DNA molecule that codes for a protein, which results in a characteristic.

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23
Q

define allele

A

a different version of a gene. there can be many different alleles of a single gene but most plants and animals and humans only carry two alleles of each gene, one from each parent.

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24
Q

define genotype

A

the genetic constitution of an organism; the alleles an organism has.

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25
Q

define phenotype

A

the expression of the genetic constitution and its interaction with the environment; an organism’s characteristics.

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26
Q

define dominant.

A

an allele whose characteristic appears in the phenotype even when there’s only one copy. dominant alleles are shown by a capital letter.

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27
Q

define recessive

A

an allele whose characteristic only appears in the phenotype if two copies are present. recessive alleles are shown by a lower case letter.

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28
Q

define co-dominant

A

alleles that are both expressed in the phenotype; neither one is recessive.

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29
Q

define locus

A

the fixed position of a gene on a chromosome. alleles of a gene are found at the same locus on each chromosome in a pair.

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30
Q

define homozygote

A

an organism that carries two copies of the same allele.

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31
Q

define heterozygote

A

an organism that carries two different alleles.

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32
Q

define carrier

A

a person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring.

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33
Q

what are genetic diagrams used for?

A

they are used to predict the genotypes and phenotypes of the offspring produced if two parents are crossed (bred)

34
Q

define monohybrid inheritance

A

this is the inheritance of a characteristic controlled by a single gene.

35
Q

what do monohybrid crosses show?

A

they show the likelihood of the different alleles of that gene being inherited by offspring of certain parents.

36
Q

what is an example of genes with codominant alleles?

A

haemoglobin with normal red blood cells and sickle cell anaemia cells.

37
Q

what is an example of genes with multiple alleles?

A

the ABO blood group system where there are 3 alleles for blood type. A and B are both dominant whilst O is recessive.

38
Q

what are dihybrid crosses used for?

A

to look at how two different genes are inherited at the same time.

39
Q

how are dihybrid crosses represented?

A

there will be the parents genotypes e.g. RrYy and RrYy.
when these are crossed it will produce the gamete alleles; RY, Ry, rY, ry for both genotypes. we will then cross each gamete alleles with each other to produce a cross such as RRYY or something.

40
Q

what is the phenotypic ratio for dihybrid crosses?

A

9:3:3:1

41
Q

explain how a characteristic can be sex-linked

A

a characteristic is sex-linked when the allele that codes for the characteristic is located on a sex chromosome.

42
Q

why doesn’t the ‘Y’ chromosome carry genes?

A

the Y chromosome is smaller than the X chromosomes and so it carries fewer genes, and so instead the genes on sex chromosomes are only carried on the X chromosome.

43
Q

why are males more likely than females to show recessive phenotypes for genes that are sex-linked?

A

the XY chromosomes only have one allele for sex-linked genes. and so because they only have one copy, they express the characteristic of this allele even if it’s recessive.

44
Q

what are autosomes?

A

chromosomes that are not sex chromosomes.

45
Q

what are autosomal genes?

A

genes located on autosomes.

46
Q

how are autosomal genes linked?

A

when genes are on the same autosome they are said to be linked. because they are on the same autosome they’ll stay together during the independent segregation of chromosomes in meiosis I.

47
Q

how does linkage work?

A

the closer together two genes are on the autosome, the more closely they are said to be linked.
if two genes are autosomally linked, you won’t get the phenotypic ratio (9:3:3:1) in the offspring of a cross.

48
Q

what can’t happen for linkage to occur?

A

the crossing over of homologous chromosomes.

49
Q

how can genetic crosses show autosomal linkage?

A

instead of the phenotypic ratio 9:3:3:1 with autosomal linkage it will be 8:1:1:8 where the two largest numbers in the cross will be the original parent phenotypes.

50
Q

what are recombinants?

A

the phenotypes that were not the original parental phenotypes in the dihyrbid crosses.

51
Q

what does the presence of recombinants show?

A

this shows that linkage was not complete and crossing over in meiosis took place.

52
Q

what is epistasis?

A

epistasis is where the allele of one gene masks (blocks) the expression of the alleles of other genes.

53
Q

explain an example of epistasis (use the flower pigment example)

A

flower pigment in a plant is controlled by 2 genes.
gene 1 codes for a yellow pigment (Y is the dominant yellow allele).
gene 2 codes for an enzyme that turns the yellow pigment orange (R is the dominant orange allele).
if we have the genotype ‘yyRr’ the pigment will be colourless, this is because there is no dominant Y allele so the pigment won’t be yellow, the pigment can then only turn orange if there is a Y allele, which there isn’t.
and so the conclusion would be that, gene 1 is epistatic to gene 2 as it can mask the expression of gene 2. in other words if gene 1 is not present this blocks gene 2 from even working.

54
Q

how many copies of the recessive epistasis allele are needed to mask the expression of the other gene?

A

2 copies (yy)

55
Q

how many copies of the dominant epistasis allele are needed to mask the expression of the other gene?

A

at least one copy (Rr/RR)

56
Q

how do dihyrbrid crosses involving a recessive epistatic allele work? (using the flower pigment example)

A

if you cross a homozygous recessive parent and a homozygous dominant parent you will get 2 heterozygous phenotypes (YyRr).
crossing the heterozygous phenotypes gives you an offspring phenotypic ratio of 9:3:4
the epistatic gene is (yy).
9= both dominant alleles
3= dominant ‘Y’ epistatic and recessive (Yyrr/YYrr)
4= recessive epistatic gene (yyRR/yyRr/yyrr)

57
Q

how do dihyrbrid crosses involving a dominant epistatic allele work? (using squash colour example)

A

if you cross a homozygous recessive parent and a homozygous dominant parent you will get 2 heterozygous phenotypes (WwYy).
crossing the heterozygous phenotypes gives you an offspring phenotypic ratio of 12:3:1
the epistatic gene is (W/w).

e.g squash colour is controlled by two genes; the colour
epistatic gene (W/w) and the yellow gene (Y/y).
the no-colour,
white allele (W) is dominant over the coloured allele (w), so WW or Ww will be white and ww will be coloured.
the yellow gene has the dominant yellow allele (Y) and the recessive green allele (y).
so if the plant has at least one W, then the squash will be white, masking the expression of the yellow gene.
crossing wwyy with WWYY gives a phenotypic ratio of 12: 3: 1
12= dominant epistatic (WWYY/WWYy/WWyy/WwYY/WwYy)
3= recessive epistatic and dominant (wwYY/wwYy)

58
Q

what is the chi-squared test and what is it used for?

A

the chi-squared test is a statistical test that is used to see if the results of an experiment support a theory. in this case it is used to check the results of genetic crosses.

59
Q

how are we able to see if the observed results support the expected results?

A

by making a hypothesis called the null hypothesis.

60
Q

what is the null hypothesis?

A

the null hypothesis is always that there is no statistically significant difference between the observed results and the expected results.
there will usually be a difference in the experimental results but it’s whether those results are due to chance or your theory is wrong.

61
Q

why is the chi-squared test carried out?

A

it is carried out to compare how well the observed results match the expected results.
the outcome either supports or rejects the null hypothesis.

62
Q

what is the formula for chi-squared?

A

the sum of, (O-E) squared / E
O= observed results
E= expected results.

63
Q

how do we find out if there’s a significant difference between our observed and expected results?

A

to find out if there is a significant difference between your observed and expected results you need to compare the chi-squared value to a critical value.

64
Q

define critical value

A

the critical value is the value of chi-squared that corresponds to a 0.05 (5%) level of probability, that the difference between the observed and expected results is due to chance.

65
Q

how do we know when the null hypothesis should be rejected or not?

A

if your chi-squared value is larger than or equal to the critical value then there is a significant difference between the observed and expected results (something other than chance is causing the difference); the null hypothesis can be rejected.
if your chi-squared value is smaller than the critical value then there is no significant difference between the observed and expected results; the null hypothesis can’t be rejected and so your theory is supported.

66
Q

what are degrees of freedom, regarding the critical values table?

A

the number of phenotypes minus one.

67
Q

define species

A

defined as a group of similar organisms that can reproduce to give fertile offspring

68
Q

define gene pool

A

the complete range of alleles present in a population

69
Q

define allele frequency

A

how often an allele occurs in a population. usually given as a percentage of the total population

70
Q

what is the hardy-weinberg principle?

A

it is a mathematical method. it predicts that the frequencies of alleles in a population won’t change from one generation to the next

71
Q

what conditions are needed for the hardy-weinberg principle to apply?

A

it has to be a large population where there’s no immigration, emigration, mutations or natural selection.
there also needs to be random mating; all possible genotypes can breed with all others.

72
Q

what are the hardy-weinberg equations?

A

p + q = 1
p squared + 2pq + q squared = 1

73
Q

what are the hardy-weinberg equations used for?

A

-they are used to calculate the frequency of particular alleles, genotypes and phenotypes within populations.
-also to test whether selection or any other factors are influencing allele frequencies; if frequencies do change between generations in a large population then there is an influence of some kind.

74
Q

how is the hardy-weinberg equation used to predict allele frequency?

A

when a gene has two alleles, you can figure out the frequency of one of the alleles of the gene if you know the frequency of the other allele.
we use the equation: p + q = 1
p- the frequency of one allele, usually the dominant one
q- the frequency of the other allele usually the recessive one

75
Q

how is the hardy-weinberg equation used predict genotype and phenotype frequency?

A

you can figure out the frequency of one genotype if you know the frequencies of the others.
we use the equation: p squared + 2pq + q squared = 1
p squared- the frequency of the homozygous dominant phenotype
2pq- the frequency of the heterozygous genotype
q squared- the frequency of the homozygous recessive genotype

genotype frequencies can be then used to work out phenotype frequencies. this is by adding the frequencies of the dominant genotypes and recessive genotypes to know the frequencies of each phenotype.

76
Q

how is the hardy-weinberg equation used to predict the percentage of a population that has a heterozygous genotype when given the recessive genotype?

A

if given a recessive genotype with values in correspondence to its frequency, we can use that to work out the frequency of a heterozygous genotype.
we will use both equations, p + q = 1 first. square root the values of the recessive genotype to find q by itself.
do 1 - q to find out p. then use the second equation, to work out the frequency of heterozygous genotype; 2pq and so use the values of p and q to find out the frequency.

77
Q

what is variation?

A

variation is the differences that exist between individuals.
variation within a species means that individuals in a population can show a wide range of different phenotypes.

78
Q

what is genetic variation?

A

where individuals of the same species have the same genes but different alleles.

79
Q

what is the main source of genetic variation?

A

mutation; where changes in the DNA base sequence leads to the production of new alleles.

80
Q

what are two other sources of genetic variation?

A

-meiosis; through the crossing over of chromatids and the independent segregation of chromosomes.
-random fertilisation of the gametes during sexual reproduction.

81
Q

define evolution.

A

where the frequency of an allele in a population changes over time.

82
Q

how does natural selection work?

A

Biology AQA (8 decks)

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