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A-level Biology > Chapter 9 - Genetic diversity and mutation > Flashcards

Chapter 9 - Genetic diversity and mutation Flashcards

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1
Q

what is a gene mutation

A

any change to the quantity or the base of the DNA of an organism

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2
Q

what is a substitution mutation

A

when one base is substituted for another

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3
Q

why are mutations bad

A

order of DNA in a gene determines the amino acid sequence which codes for a certain protein. If this is altered it may lead to the protein lacking characteristics that are important for its role

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4
Q

what is a deletion mutation

A

one base is deleted from the DNA sequence

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5
Q

why do deletion mutations cause a large change to the organisms

A

every base after the one that has been deleted experiences a frameshift and moves one to to the left because bases are read in triplets the codons aren’t read correctly

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6
Q

what will adding a base result in

A

a frameshift to the right

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7
Q

what is a silent mutation

A

because the DNA code is degenerate a substitutions mutation may result in the same amino acid being coded for and so have no effect on the organisms

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8
Q

what is a mutagenic agent

A

something that increases the likelihood of a mutation eg UV radiation and ionising radiation

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9
Q

what are chromosome mutations

A

spontaneous changes in the number of or structure of whole chromosomes

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10
Q

what are the two forms of chromosome mutations

A

changes in whole set of chromosomes changes in the number of individual chromosomes

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11
Q

when will changes to whole sets of chromosomes occur

A

when organisms have three or more sets of chromosomes rather than the normal two

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12
Q

what is a chance to a whole set of chromosomes called

A

polyploidy and it occurs mainly in plants

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13
Q

what is non-disjunction

A

when homologous pairs of chromosomes fail to separate during meiosis leading to changes in the number of individual chromosomes and sometimes syndromes like Downs

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14
Q

what causes downs syndrome

A

extra copy of chromosome 21

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15
Q

how many daughter cells are produced meiosis

A

4

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16
Q

how many divisions take place during meiosis

A

2

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17
Q

what is a haploid number

A

number of chromosomes gametes have half the normal amount

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18
Q

what is the diploid number

A

the full set of 46 chromosomes

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19
Q

what happens during the first division of meiosis

A

homologous chromosomes pair up and their chromatids wrap around each other. one chromosomes from each pair goes into one of the daughter cells

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20
Q

what happens during the second division of meiosis

A

centromere is divided and the sister chromatids move to each end of the cell

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21
Q

what is a gene

A

a length of dna that codes for a polypeptide

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22
Q

wha is the locus

A

position of a gene on a chromosome or dna molecule

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23
Q

what is an allele

A

different forms of a gene

24
Q

what are homologous chromosomes

A

one maternal and one paternal chromosome which have the same gene loci

25
Q

are daughter cells genetically different in meiosis or mitosis

A

meiosis

26
Q

process of meiosis

A

dna unravels and replicates so there are 2 copies of each chromosome.
dna forms two chromosomes made from 2 chromatids joined at the centromere
first division - chromosomes form homologs pairs which separate halving the chromosome number
second division - the centromere divides to separate the sister chromatids making up each chromosome
four genetically different haploid cells are produced

27
Q

what is independent segregation

A

each homologous pair of chromosomes comprises of one paternal and one maternal chromosome when the pair separates it is completely random which chromosomes end up in which daughter cell
the four daughter cells will have completely different combinations of maternal and paternal chromomses

28
Q

when does independent segregation occur

A

when the homologous pairs are separated during meiosis

29
Q

during which process will homologous chromosomes pair and separate

A

meiosis

30
Q

what is another war in which genetic variation is induced

A

each haploid has a very different genetic makeup and when two of these use randomly at fertilisation variety is seen in the offspring

31
Q

what is crossing over chromatids

A

homologous pairs of chromosomes pair up, chromatids twist around each other and parts of the chromatids break off due to the tension
these broken parts of chromatids usually rejoin with the chromatids of its homologous partner
this creates genetic variation in the maternal and paternal chromosomes.
chromosomes have the same genes but have different combination of alleles

32
Q

what is chiasmata

A

point at which chromosomes snap and swap alleles

33
Q

what is recombination

A

when the broken off sections of chromatids join with another chromatid

34
Q

what is the formula for the possible number of chromosomes in each daughter cell

A

2^n where n is the number pairs of homologous chromosomes

35
Q

what is the formula for the number of chromosomes in each daughter cell taking into account the random pairing gametes

A

(2^n) ^2

36
Q

what is an allele

A

different form of a gene

37
Q

what is genetic diversity

A

total number of different alleles in a population

38
Q

when is genetic diversity reduced

A

when a population has fewer alleles

39
Q

process of natural selection 6

A
  • gene pool contains wide variety in any population .
  • random mutations may result in a new allele,
  • certain environment could give the possessor an advantage, better adapted to survive competition.
  • they will live longer and grow more healthily increasing -their chance of producing offspring.
  • their offspring are likely to have the new allele and more likely to survive and reproduce
  • over time the proportion of the population with this allele will increase
40
Q

what is a genetic bottleneck

A

an event that causes a big reduction in a population

41
Q

what is the founder effect

A

just a few organisms from a population start a new colony with a very small gene pool

42
Q

why might the founder effect lead to an increase in genetic diseases

A

frequency of each allele in the new colony may be different from that of the original colony - eg rare alleles could become more common

43
Q

why could the founder effect occur

A

migration leads to geographical separation

44
Q

what is directional selection

A

population mean will move towards one extreme

45
Q

what is stabilising selection

A

population men will move more towards the average

46
Q

what is disruptive selection

A

population will have two extreme that have large and less in the average

47
Q

what will disruptive selection lead to

A

speciation

48
Q

what does direction selection do

A

changes the characteristics of.a population

49
Q

what does stabilising selection do

A

maintains the characteristics of a population

50
Q

how does directional selection work for example in bacteria

A
  • individuals will fall either left or right of the mean and posses a phenotype which is well suited to the conditions
  • these will be more likely to survive and breed
  • the bacteria that survive divide by binary fission to build a small population that was resistant
  • this population was more likely to survive and breed in the presence of penicillin
  • the number of the resistant population increased and the frequency of the advantageous allele did too.
  • this leads to a distribution curve shifting
51
Q

how does stabilising selection work

eg with babies weight

A
  • humans have a range of birth weights
  • small babies are less likely to survive because they can’t maintain their body temperature
  • large babies are less likely to survive because of north difficulties
  • conditions are more favourable to middle sized babies so the weight of human babies tends to shift towards the middle
52
Q

with what type of selection is the environment not changing

A

stabilising

53
Q

what are the three types of adaptations

A

behavioural
physiological
anatomical

54
Q

what are behavioural adaptations

A

ways that an organisms acts that increase its chance of survival and reproduction

55
Q

what are physiological adaptations

A

processes inside an organisms body that increases its chance of survival and reproduction

56
Q

what are anatomical adaptations

A

structural feutres of an organisms body which increases its chance of survival and reproduction

57
Q

why are some breeds of animals sterile

A

have an odd number of chromosomes so they can’t pair during meiosis to produce gametes

A-level Biology (19 decks)

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