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A2 biology > selection and evolution > Flashcards

selection and evolution Flashcards

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1
Q

Discontinuous variation

A

Qualitative differences fall into clearly distinguishable categories, with no intermediates – e.g. four possible ABO blood groups, the inheritance of haemophilia or sickle cell anaemia

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2
Q

genetic basis of discontinuous variation

A

1) different alleles at a single gene locus have large effects on the phenotype
2) different genes have quite different effects on the phenotype

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3
Q

continuous variation

A

variation in which many alleles have small effects on the phenotype, quantitative differences with many intermediates

e.g., height, weight

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4
Q

genetic basis of continuous variation

A

1) different alleles at a single locus have small effects on the phenotype
2) different genes have the same/additive effect on the phenotype
3) a large number of genes may have a combined effect on a particular phenotype (polygenes)

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5
Q

polygenes

A

a gene whose individual effect on a phenotype is too small to be observed, but which can act together with others to produce observable variation

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6
Q

Using named examples, describe and explain the differences between continuous variation and discontinuous variation/8
(pp)

A

discontinuous :
-few, genes control a
phenotype
-qualitative
-discrete categories / no
intermediates
-different alleles at
single gene locus have
large effect on
phenotype
-different genes have
different effects
-no, contribution by
environment to
phenotype
-example; albinism / 
sickle cell anaemia / 
blood group

continuous:
-several genes control
a phenotype
-quantitative
-range of categories / 
many intermediates
-different alleles at
single gene locus
have small effects
-environment has
considerable
influence on
phenotype
-example ; e.g. height / 
mass

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7
Q

state what arises phenotype

A

the phenotype results from the interaction between the genotype and environment

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8
Q

factors that tend to reduce phenotypic variation

A

1) dominance
2) gene interaction

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9
Q

genetic variation among individuals in a population is caused by (5)

A

1) Independent assortment of chromosomes, and therefore alleles, during meiosis
2) Crossing over between chromatids of homologous chromosomes during meiosis
3) Random mating between organisms within a species
4) Random fertilisation of gametes
5) Mutation (excluding somatic cells – apart of cells in the reproductive organs)

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10
Q

what type of mutation produces new alleles?

A

gene mutations, however the alleles formed are often recessive and do not show up frequently in populations

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11
Q

why natural selection occurs

A

1) populations have the capacity to produce many offsprings
2) offsprings compete for resources
3) individuals best adapted to survive breed and pass on their alleles

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12
Q

selection pressure

A

factors that contribute to selecting which variations will provide the individual with an increased chance of surviving over others

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13
Q

natural selection

A

effects of selection pressures on the frequency of alleles in a population

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14
Q

types of selection

A

1) stabilising
2) directional
3) disruptive

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15
Q

stabilising selection

A
  • individuals in a population with intermediate phenotypes more likely survive
  • individuals in a population with extreme phenotypes die
  • no change in environment
  • e.g., birth weight
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16
Q

directional selection

A
  • one extreme phenotype is selected for
  • the other extreme and intermediate phenotypes are selected against
    -e.g., the beak size in a population of finches
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17
Q

disruptive selection

A
  • mean intermediate selected against
  • both extremes selected for
  • bimodal distribution
  • causes genetic variation
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18
Q

factors affecting allele frequency in a population

A

1) genetic drift
2) the founder effect
3) natural selection

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19
Q

genetic drift

A

a change in the allele frequency in a small population which occurs by chance.
larger influence in small population

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20
Q

the founder effect

A
  • an example of genetic drift
  • due to migration
  • new population is establish by a small number of individuals
    • they carry a fraction of
      alleles
    • gene pool is not
      representative
    • lower genetic diversity
      than original population
21
Q

bottle neck effect

A
  • an example of genetic drift
  • large decrease in genetic diversity
  • due to natural disasters
  • gene pool will not be representative
22
Q

how natural selections affects allele frequency in a population

A

causes changes in allele frequencies with fitness-increasing alleles becoming more common in the population

23
Q

State the conditions that have to be satisfied in the Hardy Weinberg principle

A

1) no mutation
2) no natural selection
3) large population
4) no non-random breeding
5) no migration

24
Q

artificial selection

A

humans purposefully applying selection pressures to populations in order to breed ‘desirable’ traits from the natural variation among organisms

25
Q

Process of artificial selection

A

1) humans choose parents with desirable features
2) parents with desirable features are crossed
3) select offspring with desirable features
4) repeat for many generations

26
Q

disadvantages of artificial selection

A

1) inbreeding
-increase in
homozygosity
- harmful recessive
alleles may be
expressed
- inbreeding depression
- decrease in genetic
variation
2) offspring may show desired traits, but may not be well adapted to its environment

27
Q

examples of artificial selection

A

1) introducing disease resistance in wheat and rice varieties to limit loss of crops by disease
2) improving the milk yield of cattle
3) in maize, inbreeding and hybridisation to produce uniform, vigorous maize crops

28
Q

‘desirable’ features when selectively breeding cattle

A

1) increased docility (calm temperature)
2) fast growth rate
3) high milk yields
4) disease resistance

29
Q

problems associated with selectively breeding cattle

A

1) the animals are large
2) they take a long time to reach maturity
3) the gestation period is long
4) the number of offspring produced is small

30
Q

How selective breeding can be used to increase milk yield of cattle?
(pp)

A
  • humans choose cattle with high milk yield
  • humans cross breed cattle
  • humans choose offspring from desirable characteristics
  • continue for several generations
  • allele for high yield is passed on
  • increase in allele frequency of high milk yield
  • AI
31
Q

why is disease resistance introduced to varieties of wheat and rice?

A

to reduce the loss of yield resulting from infections

32
Q

why are mutant alleles for gibberellin synthesis incorporated into dwarf varieties?

A

1) most dwarf varieties carry mutant alleles for 2 reduced height (Rht) genes
2) these genes code for DELLA proteins which reduce the effect of gibberellin on growth
*another mutant allele of a different gene has its dwarfing effect as the plant cells don’t have receptors for gibberellin
3) mutant alleles increase yield by having a greater proportion of energy put into grain

33
Q

why is inbreeding and hybridisation done to produce vigorous, uniform varieties of maize?

A
  • when maize plants are inbred, the plants in each generation become progressively smaller and weaker (inbreeding depression)
  • this occurs because homozygous plants are less vigorous than heterozygous plants
  • challenge when growing maize: heterozygosity and uniformity
  • solution: hybridisation

1) using maize seeds that produce homozygous plants

2) these different homozygous varieties are crossed, producing F1 that are all the same genotype

34
Q

ideal maize characteristics

A

1) high yields
2) resistance to more pests and diseases
3) good growth in nutrient-poor soils / short water supply

35
Q

Examples of crop features that can be improved by selective breeding to increase the yield of crop
(pp)

A
  • mass
  • disease resistance
  • resistance to insects
  • rate of growth
  • drought resistance
  • resistance to herbicides
36
Q

state the general theory of evolution/2
(pp)

A
  • organisms have changed overtime
  • due to natural selection
  • due to a long period of time
  • due to variation
37
Q

how evolution occurs

A

1) organisms produce more offspring than are needed to replace the parents
2) natural populations tend to remain stable in size over long periods
3) there is competition for survival / struggle for existence
4) there is variation among the individuals of a given species
5) the best adapted variants will be selected for by natural conditions operating at the time / natural selection occurs / survival of the fittest

38
Q

comparing amino acid sequences of proteins

A

when the amino acid sequence of a particular protein is compared in different species, the number of differences gives a measure of how closely related the species are

39
Q

comparing nucleotide sequences of mitochondrial DNA

A

differences in the nucleotide sequences of mtDNA can be used to study the origin and spread of our own species

40
Q

human mtDNA

A

1) inherited through the female line
2) a zygote contains mitochondria of ovum and not sperm
3) mtDNA is circular so can’t undergo any form of crossing over ∴ changes in nucleotide sequence can only occur by mutation
4) different human populations show differences in mtDNA sequences; these provide evidence for the origin of different populations

41
Q

speciation

A

the formation of new species

42
Q

define species

A

a group of organisms with similar morphological, physiological, biochemical, and behavioural features, which can interbreed to produce fertile offspring and are reproductively isolated from other species

43
Q

types of speciation

A

1) allopatric (geographical separation)
2) sympatric (ecological & behavioural separation)

44
Q

allopatric speciation

A

speciation that occurs when 2 populations are separated from each other geographically

45
Q

what is meant by sympatric speciation?
(pp)

A

no geographical barrier
- behaivioural isolation
- reproductive isolation as no gene flow

46
Q
A
47
Q

reproductive isolation

A

the inability of 2 organisms of the same species to interbreed due to geographical separation of behavioural differences

48
Q

causes of extinction

A

1) climate change

2) competition (from better adapted species)

3) habitat loss

4) killing by humans

49
Q

Explain why species may become extinct? /7
(pp)

A
  • environment changes
  • species cannot adapt fast enough
  • climate change
  • extinct species at risk
  • predation
  • habitat loss
  • hunting by humans
  • extinct species at risk

A2 biology (9 decks)

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