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3 Genetics > 23 Meiosis > Flashcards

23 Meiosis Flashcards

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Biology 101 flashcards
1
Q

What does ‘heredity’ refer to?

A

The passing of of genes form one generation to the next.

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2
Q

What are ‘genes’?

A

Lengths of DNA which code for a specific characteristic.

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3
Q

What does ‘locus’ refer to?

A

A specific place along the chromosome, typically refers to a specific gene.

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4
Q

What do singled cells eukaryotes perform asexual reproduction?

A

Simply by mitosis and budding etc.

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5
Q

What form of cell division is used in asexual reproduction?

A

Mitosis

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6
Q

What can offspring produced by asexual reproduction be called?

A

‘Clones’.

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7
Q

What does ‘clone’ refer to?

A

An organism which is genetically identical to its parent i.e. form asexual reproduction.

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8
Q

What is a ‘life cycle’?

A

The generation-to-generation sequence of stages in the reproductive history of an organism, from conception to production of its own offspring.

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9
Q

What is a microscope image of the chromosomes of an organism called?

A

A ‘karyotype’

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10
Q

What is a ‘karyotype’?

A

A microscope image of the chromosomes of an organism

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11
Q

How can ‘karyotypes’ be useful?

A

They allow the identification of homologous chromosomes which have the same shape and length etc.

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12
Q

What are ‘homologs’?

A

‘Homologous chromosomes’

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13
Q

What are the basic types of chromosome?

A

‘Sex chromosomes’ and ‘Autosomes’

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14
Q

What are ‘autosomes’?

A

Non-sex chromosomes.

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15
Q

What are non sex chromosomes called?

A

‘Autosomes’

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16
Q

How many chromosomes do humans have?

A

46 (23 homologous pairs of autosomes + 2 ‘sex chromosomes’)

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17
Q

What are the chromosomes inherited from the mother called?

A

The ‘maternal set’

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18
Q

What does ‘maternal set’ refer to?

A

The chromosomes inherited from the mother

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19
Q

What are the chromosomes inherited from the father called?

A

The ‘paternal set’

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20
Q

What does ’paternal set’ refer to?

A

The chromosomes inherited from the father

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21
Q

What is a fertilised egg called?

A

A ‘zygote’

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22
Q

What are the basic ’sexual life cycles’?

A

In animals a diploid adult undergoes meioses to produce haploid gamete. Two gametes fuse during ‘fertilisation’ to form a diploid zygote which grows through mitosis.

Plants and some algae undergo ‘alternation of generations’ in which a diploid adult (’sporophyte’) releases haploid spores (seeds etc.) which contain ‘haploid gametophytes’ these gametophytes produce gametes which combine to form a diploid ’sporophyte’

in most fungi and some protists, including some algae:

After gametes fuse and form a diploid zygote, meiosis occurs without a multicellular diploid offspring developing. Meiosis produces not gametes but haploid cells that then divide by mitosis and give rise to either unicellular descendants or a haploid multicellular adult organism. Subsequently, the haploid organism carries out further mitoses, producing the cells that develop into gametes. The only diploid stage found in these species is the single-celled zygote.

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23
Q

What is meiosis divided into?

A

(Interphase), Meiosis I and Meiosis II

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24
Q

Broadly speaking, what happens in interphase before meiosis?

A

A pair of homologous chromosomes come to ether and are duplicated to for tetrads

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25
Q

Broadly speaking, what happens during meiosis I?

A

The tetrads undergoes crossing over before the homologous chromosomes are separated.

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26
Q

Broadly speaking, what happens during meiosis II?

A

The homologous chromosome are separated to form 4 genetically distinct gametes. Each is haploid and thus has a single copy of each chromosome/allele

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27
Q

What are the stage of meiosis?

A

Prophase I, Metaphase I, Anaphase I, Telophase I and cytokinesis. then:

Prophase II, Metaphase II, Anaphase II, Telophase II and cytokinesis.

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28
Q

How does the cell appear before Prophase I of meiosis?

A

Tetrads has formed of two sets of ‘sister chromatids’ they are joined by ‘chiasmata’.

The homologous chromosomes have condensed and are tightly bound together

The nuclear envelope has fragmented.

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29
Q

What are ‘chiasmata’?

A

The places at which the homologous chromosomes are joined and thus mark the points where crossing over occurs (chiasmata = chiasma)

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30
Q

What happens during Prophase I of meiosis?

A

Chromosomes begin to condense. Homologous chromosomes pair to form tetrads/bivalents. These paired homologs are connected along their lengths by a protein structure called the ‘synaptonemal’ complex. This state is called ‘synapsis’.

Crossing over, the exchange of genetic information between non-sister chromatids occurs before and during ’synapsis’

After crossing over the ’synaptonemal complex’ release the tightly bound homologous chromosomes and thus ’synapsis’ ends. The sister chromatids are still tightly bound in ‘chromatid cohesion.’

The homologous chromosomes are bound only at the places where crossing over has occur. These places are called the ‘chiasmata’

Centrosome movement, spindle formation, and nuclear envelope breakdown occur
as in mitosis.

Microtubules from one pole or the other attach to the two kinetochores, protein structures at the centromeres of the two homologs. The homologous pairs then move toward the metaphase plate.

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31
Q

What are ’tetrads’?

A

Bivalents

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32
Q

What is the state in which the homologous chromosomes are tightly bound called?

A

Synapsis.

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33
Q

What does ’synapsis’ refer to?

A

The state in which the homologous chromosomes are tightly bound

34
Q

What causes ’synapsis’?

A

They are held together by the ’synaptonemal complex’ which is a protein structure.

35
Q

What is the ‘synaptonemal complex’?

A

A protein structure which hold the homologous chromosomes together.

36
Q

What happens during Metaphase I of meiosis?

A

Pairs of homologous chromosomes are arranged at the metaphase plate, with one chromosome in each pair facing each pole (independent assortment)

Both chromatids of one homologous chromosome are attached to kinetochore microtubules from one pole. Those of the other homolog are attached to microtubules from the opposite pole.

37
Q

What happens during Anaphase I of meiosis?

A

Breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate.

The homologs move toward opposite poles, guided by the spindle apparatus.

Sister chromatid cohesion persists at the centromere, causing chromatids to move as a unit toward the same pole.

38
Q

What happens during Telophase I of Meiosis?

A

At the beginning of telophase I, each half of the
cell has a complete haploid set of duplicated chromosomes.

Each chromosome is composed of two sister chromatids; one or both chromatids include regions of nonsister chromatid DNA.

39
Q

What happens during cytokinesis after meiosis I?

A

Cytokinesis (division of the cytoplasm) usually occurs simultaneously with telophase I, forming two haploid daughter cells.

In animal cells like these, a cleavage furrow forms. (In plant cells, a cell plate forms.)

In some species, chromosomes decondense and nuclear envelopes form.

40
Q

What is the process which splits one cell into two?

A

Cytokinesis

41
Q

What is cytokinesis’?

A

The splitting of the cytoplasm so that two cell form from one.

42
Q

What are the constituents of chromosomes?

A

Chromatids

43
Q

What terms can describe chromatids?

A

’Sister chromatids’ and ’Non-sister chromatids’

44
Q

What are ’sister chromatids’?

A

Chromatids which have identical genetic material and thus arise from a single duplicated chromatid.

45
Q

What are ’non-sister chromatids’?

A

Chromatids which are homologous but have different alleles.

46
Q

What are genetically identical chromatids called?

A

’Sister chromatids’

47
Q

What are homologous chromatids with different genetic material called?

A

’Non-sister chromatids’

48
Q

What happens during ‘Prophase II’ of meiosis?

A

A spindle apparatus forms.

In late prophase II chromosomes, each still composed of two chromatids associated at the centromere, move toward the metaphase II plate.

49
Q

What happens during ‘Metaphase II’ of meiosis?

A

The chromosomes are positioned at the metaphase plate as in mitosis.

Because of crossing over in meiosis I, the two sister chromatids of each chromosome are not genetically identical.

The kinetochores of sister chromatids are attached to microtubules extending from opposite poles.

50
Q

What happens during ‘Anaphase II’ of meiosis?

A

Breakdown of proteins hold- ing the sister chromatids together at the centromere allows the chromatids to separate.

The chromatids move toward opposite poles as individual chromosomes due to the action of the spindle.

51
Q

What happens during ‘Telophase II’ and cytokinesis of meiosis?

A

Nuclei form, the chromosomes begin decondensing, and cytokinesis occurs to split the cell’s cytoplasm into two.

Therefore 4 genetically distinct cells have been produced.

52
Q

How does mitosis differ from meiosis in terms of the number of steps?

A

Mitosis has ‘Prometaphase’ which meiosis does not.

53
Q

What are the basic properties of meiosis and mitosis that can be compared and contrasted?

A
  • DNA replication
  • Number of divisions
  • Synapsis of homologous chromosomes
  • Number of daughter cells and genetic composition
  • Role in the animal body
54
Q

Compare and contrast mitosis and meiosis based on DNA replication?

A

DNA replication during interphase before both of them.

55
Q

Compare and contrast mitosis and meiosis based on Number of divisions?

A

In mitosis one division occurs including prophase, prometaphase, metaphase, anaphase, and telophase.

In meiosis two division occur, each including prophase, metaphase, anaphase, and
telophase.

56
Q

Compare and contrast mitosis and meiosis based on synapsis?

A

It does not occur in mitosis

In meiosis it occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion

57
Q

Compare and contrast mitosis and meiosis based on number of daughter cells and their properties?

A

Mitosis produces two daughter cells, each diploid (2n) and genetically identical to the parent cell.

Meiosis produces four daughter cells, each haploid (n), containing half as many chromosomes as the parent cell. Each daughter cell genetically different from the parent cell and from each other

58
Q

Compare and contrast mitosis and meiosis based on role in the animal life cycle?

A

Mitosis enables multicellular adult to arise from zygote. It produces cells for growth, repair, and, in some species, asexual reproduction.

Meiosis produces gametes; reduces number of chromosome sets by half and introduces genetic variability among the gametes.

59
Q

What are the unique events which occur during meiosis?

A

Synapsis, crossing-over, “homologous pairs at the metaphase plate” and the separation of homologous chromosomes.

60
Q

How are the sister chromatids held together?

A

By proteins called ‘cohesins’

61
Q

What can meiosis I also be called and why?

A

‘Reductional division’ because it halves the number of chromosome sets per cell-a reduction from two sets (the diploid state) to one set (the haploid state).

62
Q

What can meiosis II also be called?

A

‘Equational division’

63
Q

What does ’reductional division’ refer to?

A

Meiosis I because it halves the number of chromosome sets per cell-a reduction from two sets (the diploid state) to one set (the haploid state).

64
Q

What does ’equational division’ refer to?

A

Meiosis II

65
Q

What are the basic processes of Meiosis that lead to variation?

A

‘Independent assortment’, ‘crossing over’ and ‘random fertilisation’

66
Q

What is ‘independent assortment’ and how does it lead to variation?

A

During metaphase I each homologous pair lines up randomly at the metaphase plate.

There the gamete receives a random mixture of parental and maternal chromosomes.

67
Q

What does ’reductional division’ refer to?

A

Meiosis I as it halves the the number of chromosomes per cell

68
Q

What does ’equational division’ refer to?

A

Meiosis II

69
Q

How many chromosomes do humans have?

A

46 (22 pairs of autosomes + 2 sex chromosomes)

70
Q

In what meiotic stage does independent assortment occur?

A

Metaphase I

71
Q

Does indépendant assortiment occur during Metaphase II?

A

Nope.

during metaphase II the recombinant chromatids assort independently but this is technically not

72
Q

What does ’crossing over’ refer to?

A

The process which occurs during meiosis in which genetic information is exchanged between homologous non-sister chromatids.

73
Q

What are chromatics that have undergone crossing over called?

A

Recombinant chromosomes

74
Q

What does ’recombinants’ refer to?

A

In the context of meiosis: chromatids which have undergone crossing over and thus are a mixture of maternal and paternal DNA.

75
Q

What does ’recombination’ refer to?

A

Crossing over.

76
Q

During what phase of meiosis does crossing over occur?

A

It begins during early prophase I

77
Q

How specifically does crossing over lead to variation?

A

It allows linked genes carried on the same chromosome to be separated and thus inherited independently.

During Metaphase II the chromosomes which contain recombinant chromatids assort independently (although this is technically not independent assortment)

78
Q

What is ‘random fertilisation’?

A

The idea that the male produces many unique gametes, as does the female.

As it is random which sperm fertilises the egg ‘random fertilisation’ increases total number of zygote combinations.

79
Q

What is the idea in which the specific gametes which fuse is random?

A

‘Random fertilisation’

80
Q

How can genetical variation be increased in asexually reproducing species?

A

Through ‘horizontal gene transfer’

81
Q

What does ’horizontal gene transfer’ refer to?

A

The process by which genetic information is passed between organisms of the same or different species.

82
Q

What is ‘horizontal gene transfer’ used for?

A

In many asexually reproducing species it is used to increase genetic variation.

In viruses it is used to inject DNA into their hosts and thus cause the production of viral proteins.

3 Genetics (9 decks)

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