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Biology A Level > Variation > Flashcards

Variation Flashcards

1
Q

what is intraspecific variation?

A

differences in organisms of the same species

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2
Q

What is a species ?

A

a group of organisms that can breed together to produce fertile offspring

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3
Q

What are the features of continuous variation?

A
  • no distinct categories
  • tends to be quantitative
  • controlled by many genes
  • strongly influenced by the environment
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4
Q

what are the features of discontinuous variation ?

A
  • distinct categories
  • tends to be qualitative
  • controlled by a few or one gene
  • unaffected by the environment
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5
Q

how can you measure dispersion ?

A

standard deviation and range

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6
Q

what is a mutation ?

A

a change in the DNA base sequence

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7
Q

what is a base substitution ?

A

The replacement of one base with a different base, eg. A -> C

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8
Q

what is a deletion mutation ?

A

A mutation removing a base from the sequence, affecting all codons downstream (also known as frame shift)

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9
Q

at what stage in meiosis does crossing over occur ?

A

Prophase 1

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10
Q

what is non-dysjunction

A

homologous pairs of chromosomes fail to separate at meiosis

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11
Q

what is hybridisation ?

A

combining the genes of 2 different species

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12
Q

what is a haploid cell

A

a cell with one complete set of chromosomes

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13
Q

what is a diploid cell

A

a cell with two complete sets of chromosomes

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14
Q

give examples of chromosomal abnormalities in humans (polyploidy)

A

Down’s syndrome (extra 21st chromosome)
Turners syndrome
Klinefelters syndrome

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15
Q

what happens to some plants with chromosomal abnormalities ?

A

they have a larger organ size and larger biomass

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16
Q

are gametes haploid or diploid cells ?

A

haploid

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17
Q

What is a phylogenetic group?

A

A group with similar evolutionary origins and relationships.

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18
Q

What is a hierarchy?

A

A system where smaller groups are placed into larger groups with no overlap. Each group is known as a taxon.

19
Q

What is a binomial expression of an organism?

A

The genus and species of an organism, represented in italics, with the genus with a capital and species without.
Eg. Homo sapiens

20
Q

Give the hierarchy of a species, from highest taxon to lowest taxon

A 
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
21
Q

How can biologists compare the genetic diversity between species ?

A

Comparing -the frequency of measurable or observable characteristics

  • The base sequence of DNA
  • The base sequence of mRNA
  • the amino acid sequence of proteins coded by mRNA
22
Q

What is the significance of courtship?

A

Courtship behaviour is essential for successful reproduction and for species recognition.
It also synchronises mating behaviour (if both are sexually mature and in season)
It can also form a pair bond which will ensure the survival of the offspring

23
Q

What are courtship rituals?

A

A sequence of actions which are unique to each species.

24
Q

Give examples of courtship rituals in nature?

A

They can include a sequence of dance moves, sounds, release of pheromones, display of colourful feathers or fighting

25
Q

How can we study courtship relationships to study species?

A

The more similar a courtship sequence is between different species, the more closely related a species is.

26
Q

What is genetic diversity?

A

The number of different alleles of genes in a population

27
Q

What is evolution?

A

The change of allele frequency over many generations in a population

28
Q

Describe natural selection.

A
  • new alleles for a gene are created by random mutations
  • if the new alleles increase the chance of surviving, they are more likely to reproduce
  • they are then more likely to pass on that advantageous allele to the next generation
  • over many generations the new allele increases in frequency
29
Q

Describe directional selection

A

One of the extremes has the selective advantage. It occurs when there is a change in the environment. The normal shifts, and becomes more common (bell shifts and becomes taller and narrower)

30
Q

Describe stabilising selection.

A

The normal/modal trait has the selective advantage. Occurs when there is no change in the environment. The modal trait remains the same. The standard deviation decreases, as individuals with the extreme trait decrease.

31
Q

Describe the first half of meiosis.

A

Prophase 1- Chromatids condense and arrange themselves into homologous pairs. Crossing over occurs. The nuclear envelope disintegrates.
Metaphase 1 - Homologous chromosomes line up along the equator and attach to the centromeres
Anaphase 1 - Homologous chromosomes are separated
Telophase 1 - chromosomes reach opposite poles of the cell. Nuclear envelope forms. Cytokinesis occurs.

32
Q

Describe the second half of meiosis.

A

Prophase 2 - Chromosomes condense, nuclear envelope disintegrates
Metaphase 2 - Spindle fibres attach to the centromeres
Anaphase 2 - sister chromatids are separated
Telophase 2 - Chromatids reach opposite poles of the cell. Nuclear envelope forms and cytokinesis occurs. Four unique daughter cells are produced.

33
Q

Describe independent segregation

A

Depending on the order in which chromosomes line up along the equator of the cell during metaphase, different combinations of chromosomes will end up in each gamete. This is random, resulting in a huge number of possibilities of combinations in the gametes.

34
Q

Describe crossing over.

A

During prophase 1 of meiosis, crossing over occurs. This is when homologous chromosomes exchange genetic material

35
Q

Describe natural selection?

A

Individuals within a species may show a wide range of variation. Predation, disease and competition result in differential survival and reproduction. Those organisms with a selective advantage are more likely to survive, reproduce and pass on their alleles to the next generation.

36
Q

What may cause an organism to go extinct?

A

New predators, removal of food sources, evolved diseases, altered climates leading to increases in other diseases, competition for all factors, affected by changes caused by humans.

37
Q

What conditions are needed for constant allele frequencies from generation to generation ?

A
  • Large population (no founder or bottleneck effect.
  • Random mating
  • No selection (ie alleles are equally likely to be passed on).
  • No migration
  • No mutation
38
Q

What are the three types of selection?

A

Stabilising, directional and disruptive

39
Q

Describe disruptive selection

A

The extreme phenotypes are the favourable trait, rather than the mean/mode. It eventually results in two separate gene pools.

40
Q

What is speciation?

A

The evolution of new species from existing ones

41
Q

For a new species to develop what must there be?

A
  • Isolation (a population needs to be separated and exposed to different environment).
  • Mutation (introduces change to the gene pools of the two populations).
  • Selection (to bring about enough change in the gene pool to make interbreeding impossible).
  • Time (to enable selection to act on the phenotypes and cause a large number of changes).
42
Q

Give some examples of isolating mechanisms that lead to speciation.

A

Geographical (populations are isolated by physical barriers).
Ecological (populations inhabit different habitats within the same area and so individuals rarely meet).
Temporal (the breeding seasons of each population do not coincide so they do not interbreed).
Behavioural (courtship variations prevent mating).

43
Q

What are the features of allopatric speciation ?

A
  • Geographical isolation
  • Creates separate gene pools with no interbreeding
  • Variation due to mutation
  • Different selection pressures
  • Differential reproductive success
  • Leads to change in allele frequency
  • Occurs over a long period of time
  • Populations no longer able to interbreed
44
Q

What are the features of sympatric speciation?

A
  • Occurs in the same population
  • Mutations cause variation
  • Reproductive separation with no gene flow
  • Different alleles selected
  • Change in allele frequency
  • Disruption selection
  • Eventually different species unable to interbreed.

Biology A Level (23 decks)

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