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Biology > 9. GENETIC DIVERSITY > Flashcards

9. GENETIC DIVERSITY Flashcards

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1
Q

Define variation

A

Differences between individuals

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2
Q

State what interspecific variation is

A

Variation between species

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3
Q

State what intraspecific variation is

A

Variation within a species

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4
Q

Which two factors contribute to phenotypic variation?

A

Genetic variation and environmental factors

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5
Q

Define discontinuous variation

A

Variation that falls into distinct categories

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6
Q

Give an example of discontinuous variation in humans

A

Blood group, sex

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7
Q

Define continuous variation

A

Variation that shows gradations from one extreme to the other

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8
Q

Give an example of continuous variation in humans

A

Height, weight

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9
Q

Why might individuals in the same family / species show phenotypic similarities?

A

Because they share genetic similarities

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10
Q

Why might individuals in different families / species show phenotypic differences?

A

Because they have genetic differences

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11
Q

Phenotypic characteristics can be under monogenic control. What does this mean?

A

The phenotype is controlled by one gene

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12
Q

Phenotypic characteristics can be under polygenic control. What does this mean?

A

The phenotype is controlled by many genes

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13
Q

Are phenotypic characteristics that are under monogenic control more likely to be continuous or discontinuous?

A

Discontinuous

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14
Q

Are phenotypic characteristics that are under polygenic control more likely to be continuous or discontinuous?

A

Continuous

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15
Q

Describe the structure of a chromosome

A

A long strand of wound up chromatin

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16
Q

How many chromosomes do human somatic cells have?

A

23 pairs / 46

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17
Q

How many chromosomes do human gametes have?

A

23

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18
Q

Which type of cells have a diploid number of chromosomes?

A

Somatic cells (body cells)

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19
Q

Define what homologous chromosomes are

A

Chromosomes with the same genes at the same loci

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20
Q

In terms of n, write a haploid number of chromosomes

A

n

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21
Q

In terms of n, write a diploid number of chromosomes

A

2n

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22
Q

Which process is this showing: n + n = 2n ?

A

Fertilisation (gametes fusing)

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23
Q

Define what sister chromatids are

A

Identical copies of the same chromosome

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24
Q

When are sister chromatids formed?

A

DNA replication

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25
Q

How are sister chromatids held together?

A

By centromeres

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26
Q

Meiosis is a type of cell division that produces which type of cells?

A

Gametes

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27
Q

How many nuclear divisions occur in meiosis?

A

Two - meiosis 1 and meiosis 2

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28
Q

When is the only time DNA replication occur in meiosis?

A

In interphase before meiosis 1

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29
Q

Describe what happens in metaphase 1 in meiosis

A

Homologous chromosomes randomly assort when they line up on the equator of the cell. Crossing over occurs between adjacent non-sister chromatids.

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30
Q

Describe what random assortment is

A

The random positioning of the maternal and paternal chromosome in a homologous pair either side of the equator of the cell

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31
Q

Define crossing over

A

Equal lengths of alleles are exchanged between the non-sister chromatids in meiosis 1

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32
Q

Describe how crossing over occurs

A

Chiasmata form between homologous chromosomes to form a bivalent. Equal lengths of alleles break and rejoin onto different chromatids.

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33
Q

Describe what a bivalent is

A

Four chromatids held together by a chiasmata

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34
Q

Describe what chiasmata is

A

The point of contact where two non-sister chromatids have twisted around each other in a bivalent

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35
Q

Describe what happens in anaphase 1 in meiosis

A

Homologous chromosomes are pulled to the poles of the cell

36
Q

Describe the chromosome number in the cells produced from meiosis 1

A

Diploid / 2n

37
Q

Describe what happens in metaphase 2 in meiosis

A

Sister chromatids line up on the equator of the cell

38
Q

Describe what happens in anaphase 2 in meiosis

A

Sister chromatids are pulled to the poles of the cell

39
Q

Describe the daughter cells are formed from meiosis

A

Four genetically non-identical, haploid cells (gametes)

40
Q

State the number of chromosomes present in each daughter cell produced from meiosis in humans

A

23 single chromosomes

41
Q

State the formula to calculate the number of different possible combinations of chromosomes of each daughter cell produced from meiosis

A

2^n where n = haploid number of chromosomes

42
Q

Calculate the number of possible chromosome combinations in gametes produced from meiosis in an organism with a diploid chromosome number of 18

A

2^(18/2) - 2^9 = 512

43
Q

State the formula to calculate the the possible number of different combinations of chromosomes in zygotes following random fertilisation of two gametes

A

(2^n)^2 where n = haploid number of chromosomes

44
Q

Calculate the number of possible combinations of chromosomes in zygotes following random fertilisation of two gametes whose cells have a diploid number of 66

A

(2^(66/2))^2 = (2^33)^2 = 8589934592^2 = 7.38 x 10^19

45
Q

Compare the number of nuclear divisions that occur in mitosis and meiosis

A

Mitosis has one nuclear division, whereas meiosis has two

46
Q

Compare the daughter cells produced from mitosis and meiosis

A

Mitosis produces two genetically identical diploid daughter cells, whereas meiosis produces four genetically non-identical haploid daughter cells

47
Q

Describe three things that occur in meiosis that don’t occur in mitosis

A

Homologous chromosomes separate, crossing over, and random assortment

48
Q

Describe what chromosome mutation is

A

Changes in the structure or number of whole chromosomes

49
Q

Describe what chromosome non-disjunction is

A

When individual homologous pairs of chromosomes or chromatids fail to separate during meiosis

50
Q

Describe non-disjunction if it occurred in meiosis 1

A

Homologous chromosomes fail to separate (during anaphase 1)

51
Q

Describe non-disjunction if it occurred in meiosis 2

A

Sister chromatids fail to separate (during anaphase 2)

52
Q

What would the result of chromosome non-disjunction be?

A

The gametes produced would either have missing or extra chromosome(s) compared to normal.

53
Q

Which gametes produced from chromosome non-disjunction will not be able to fuse with another gamete during fertilisation?

A

Gametes that have fewer than the haploid number of chromosomes

54
Q

Which gametes produced from chromosome non-disjunction will be able to fuse with another gamete during fertilisation?

A

Gametes that have more than the haploid number of chromosomes

55
Q

Name the two types of ploidy that describes the chromosome number in the gametes produced from chromosome non-disjunction

A

Polyploid and aneuploidy

56
Q

Define polyploidy

A

A change in the number of whole sets of chromosomes

57
Q

An example of polyploidy is cells that are triploid. Using n, write the shorthand for a triploid number of chromosomes

A

3n

58
Q

Using n, write the formula to show the gametes that would have fertilised to produce a triploid zygote

A

n + 2n = 3n

59
Q

An example of polyploidy is cells that are tetraploid. Using n, write the shorthand for a tetraploid number of chromosomes

A

4n

60
Q

Using n, write the formula to show the gametes that would have fertilised to produce a tetraploid zygote

A

2n + 2n = 4n

61
Q

In which organisms does polyploidy most commonly occur?

A

Plants

62
Q

Define aneuploidy

A

A change in the number of individual chromosomes

63
Q

Using n, write the shorthand for the aneuploidy gametes produced from a chromosome non-disjunction event if one pair of sister chromatids failed to separate during meiosis 2

A

n+1, and n-1

64
Q

Give an example of a human condition caused by an aneuploidy gamete being created from a chromosome non-disjunction event in meiosis

A

Down’s Syndrome

65
Q

Down Syndrome is produced when cells contain an extra copy of chromosome 21 (three copies instead of two). How many chromosomes in total would someone’s somatic cells have if they have Down’s Syndrome?

A

47

66
Q

When can organisms not produce all fertile gametes?

A

When their diploid cells have an odd number of chromosomes

67
Q

Why can organisms with an odd number of chromosomes in their diploid cells not produce all fertile gametes?

A

Because half of their gametes would not be haploid, and could therefore not pair with another gamete during fertilisation

68
Q

Define genetic variation between individuals

A

Differences in the base sequence of DNA

69
Q

Define genetic variation of a population

A

The total number of different alleles in a population

70
Q

Recall the five factors that cause genetic variation

A

Mutation
Random fertilisation
Random assortment
Crossing over
Chromosome non-disjunction

71
Q

Which of the five factors that cause genetic variation will always occur in meiosis?

A

Random assortment and crossing over

72
Q

Describe how random assortment in meiosis 1 produces genetic variation in the gametes

A

Each gamete has a different combination of maternal and paternal chromosomes

73
Q

Describe how crossing over in meiosis 1 produces genetic variation in the gametes

A

Each chromatid will contain a different combination of alleles

74
Q

What effect does selection have on genetic variation in populations?

A

Selection reduces genetic variation in populations

75
Q

Name the two types of reproduction

A

Sexual and asexual

76
Q

Name the type of asexual reproduction that occurs in bacteria

A

Binary fission

77
Q

In which type of reproduction are genetically identical offspring produced?

A

Asexual

78
Q

In which type of reproduction are genetically non-identical offspring produced?

A

Sexual

79
Q

In populations that reproduce asexually, what is the only way genetic variation is produced?

A

Mutation

80
Q

Apart from genetic variation, how else can phenotypic variation be produced in populations that reproduce asexually?

A

Environmental factors

81
Q

Why do organisms that reproduce sexually have an even number of chromosomes?

A

So during meiosis, the chromosome can be split into two haploid cells of an equal number. This means the diploid number of chromosomes can be restored during fertilisation.

82
Q

Describe the advantages of reproducing asexually

A

There are fewer stages so reproduction is quicker.
A higher number of offspring can be produced.
There is only one parent so a new environment can be colonised easily.
Clones are produced so phenotypes are always maintained.

83
Q

Describe the disadvantages of reproducing asexually

A

It decreases genetic diversity which decreases the chances of survival.

84
Q

Describe the advantages of reproducing sexually

A

It increases genetic diversity which increases the chances of survival.

85
Q

Describe the disadvantages of reproducing sexually

A

There are more stages so reproduction is slower.
A lower number of offspring can be produced.
Two parents are required so it’s more difficult to colonise new areas.
Genetically different offspring are produced so phenotypes are not always maintained.

Biology (26 decks)

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