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Grade 11 bio > Meiosis > Flashcards

Meiosis Flashcards

1
Q

what is meiosis

A

the process of cell division in eukaryotes consisting of 2 consecutive cell divisions (meiosis 1 and meiosis 2)

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2
Q

when does DNA synthesis occur

A
  • happens only once and after their is 2 nuclear divisions
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3
Q

what does the two nuclear divisions result in

A
  • 1 diploid (2n) parent cell which produces 4 haploid daughter cells
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4
Q

what are haploid cells also known as

A

gametes

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5
Q

where does meiosis happen

A

testis and ovary

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6
Q

what does the fusion of 2 haploid gametes produce

A

a diploid zygote

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7
Q

what does meiosis do

A
  1. produces 4 haploid cells from a single diploid cell
  2. it scrambles information in alleles. creating genetic diversity and is accomplished by crossing over and independent assortment
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8
Q

why do we need meiosis

A
  • it halves the number of chromosomes in sex cells
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9
Q

why does meiosis halve the number of chromosomes in sex cells

A

the sperm and egg each have 23 chromosomes so that when they come together they have 46 chromosomes

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10
Q

What are the stages of Meiosis

A
  • Meiosis 1
  • Meiosis 2
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11
Q

what happens during meiosis 1

A
  • the homologous chromosomes get separated
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12
Q

what happens in meiosis 2

A
  • sister chromatids get separated
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13
Q

what happens during prophase 1

A
  • duplicated chromosomes align with their homologues (synapsis) to form homologous pairs
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14
Q

what is a tetrad

A

the 4 chromatids of a homologous pair

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15
Q

what is crossing over

A

the exchange of segments between non sister chromatids during synapsis

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16
Q

what is chiasmata

A

the sites where chromosomes attach so they exchange genetic material

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17
Q

what are homologous chromosomes

A
  • pair of chromosomes (one maternal and one paternal) that are similar in shape and size
  • carry genes controlling the same inherited traits at the same locus
  • each locus is the same position on homologues
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18
Q

what are the types of chromosomes that humans have

A
  • autosomes
  • sex chromosomes
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19
Q

how many autosomes and chromosomes do humans have

A
  • 22 pairs of autosomes
  • 1 pair of sex chromosomes
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20
Q

what happens during metaphase 1

A
  • chromosomes (homologous pairs in tetrads) line up at the equator
  • they get attached to spindle fibres at their centromeres
  • spindle fibres connect them to the centrioles
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21
Q

what happens during anaphase 1

A
  • the spindle guides the movement of the chromosomes toward the poles
  • the homologous pairs of chromosomes separate and move toward the opposite poles as spindle fibres contract
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22
Q

What happens during Telophase 1 and cytokinesis

A
  • cytokinesis occurs simultaneously with telophase 1
  • this is the end of the first meiotic cell division
  • the cytoplasm divides, forming two new daughter cells
  • each newly formed cells has half the number of the parent chromosomes
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23
Q

what is meiosis 1 also called

A

reduction division

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24
Q

what is cytokinesis

A
  • in plant cells: cells plate forms that grows outward forming 2 daughter cells
  • in animal cells: cleavage furrow pinches inward to form 2 daughter cells
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25
Q

When does meiosis 2 begin

A

-similar to mitosis
- right after telophase 1 and cytokinesis
- no further replication of chromosomes and no interphase 2

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26
Q

what happens during prophase 2

A

-each daughter cell forms a spindle, usually at right angle to the first spindle
- chromosomes (with 2 chromatids) move toward the equator
- no crossing over happens

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27
Q

what happens during metaphase 2

A
  • the chromosomes are positioned on the metaphase plate in a mitosis like fashion
  • no homologous pairs
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28
Q

what happens during anaphase 2

A
  • centromere of sister chromatids separate and move toward opposite poles
  • individual chromosomes after anaphase 2 have only one chromatid
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29
Q

what happens during telophase 2 and cytokinesis

A
  • nuclei form at opposite poles of the cell and cytokinesis occurs
  • after cytokinesis there are 4 haploid daughter cells
30
Q

When can individual chromosomes be seen

A
  • when they are in prophase and metaphase cause they have condensed enough to be seen under a light microscope
31
Q

how are karyotypes storted

A
  • size
  • position of centromere
  • pattern of dark and light bands
32
Q

what is a karyotype

A
  • method of organizing the chromosomes of the cell in relation to number, size, and type
  • generally organized from largest to smallest chromosomes
33
Q

what are the different types of chromosomes that are based on the position of the centromere

A
  • telocentric chromosome
  • acrocentric chromosome
  • submetacentric chromosome
  • metacentric chromosome
34
Q

what is a telecentric chromosome

A

a chromosome whose centromere is located at one end

35
Q

what is a acrocentric chromosome

A

a chromosome whose centromere is located near the end

36
Q

what is a submetacentric chromosome

A

a chromosome whose centromere is located near the middle

37
Q

what is a metacentric chromosome

A

a chromosome whose centromere is centrally located

38
Q

what are the key differences between mitosis and meiosis

A
  • synapse, chiasma formation and crossing over in meiosis
39
Q

why is genetic recombination important

A

leads to variation or diversity in a population

40
Q

why is variation important

A

important raw material for natural selection and evolution helps to adapt to changing environments

41
Q

how does meiosis create genetic variation

A
  • sexual reproduction - fusion of sperm & egg/ egg & pollen
  • crossing over (prophase 1)
  • independent assortment (metaphase 1)
42
Q

what happens during sexual reproduction

A

fusion of sex cells (egg and sperm) of two individuals to form an offspring that inherits genetic information form both parents

43
Q

what is spermatogenesis

A

the process in which four sperms are produced in male testes by the process of meiosis

44
Q

what is oogenesis

A

the process in which one ovum and 3 polar bodies are produced in female ovaries by the process of meiosis

45
Q

what is fertilization

A

the process by which a sperm fuses with an egg to form a zygote and restore the diploid number of the species

46
Q

why can spermatogonia and oogonia reproduce

A
  • they have 46 chromosomes which is the number needed to do mitosis
47
Q

what are the phases in spermatogenesis and oogenesis

A
  1. multiplication phase
  2. growth phase
  3. differentiation phase
48
Q

what happens during the multiplication phase in spermatogenesis

A

one diploid spermatogonium multiplies to become 2 primary diploid spermatocytes

49
Q

what happens during the growth phase in spermatogenesis

A

each of the primary spermatocytes split and become 2 secondary haploid spermatocytes

50
Q

what happens during the differentiation phase in spermatogenesis

A

each secondary spermatocytes becomes 2 haploid spermatids which then become sperm

51
Q

what happens during the multiplication phase in oogenesis

A

one diploid oogonium multiples to become 2 primary diploid oocytes

52
Q

what happens during the growth phase in oogenesis

A

each primary oocytes becomes a secondary haploid oocyte and the first polar body

53
Q

what happens during the differentiation phase in oogenesis

A

the secondary oocyte splits to become a haploid ootid and first polar body grows a second polar body which then becomes the ovum

54
Q

what does crossing over do

A

creates new combinations of genetic material

55
Q

what is independent assortment

A
  • orientation of each chromosome pair is random with respect to other chromosome pairs in metaphase 1
  • daughter cells inherit a mix of maternal and paternal chromosomes
  • produces 2^23 gametes
56
Q

what happens if there are errors in meiosis

A
  • humans get disorders called syndromes
  • e.g. down syndrome
57
Q

how do errors in meiosis happen

A
  • happens in non-disjunction
58
Q

what is non-disjuction

A
  • when chromosomes fail to separate
59
Q

when can non disjunction happen during meiosis

A
  • anaphase 1 when homologous pairs fail to separate
  • anaphase 2 when sister chromatids fail to separate
60
Q

What happens during non-disjunction in anaphase 1

A
  • homologous pairs fail to separate
  • two gametes get an extra chromosome (trisomy; n+1); two gametes get none (n-1)
  • abnormal gametes: 100%
61
Q

what happens during non-disjunction in anaphase 2

A
  • sister chromatids fail to separate
  • two gametes are normal (n), one has an extra chromosome (trisomy: n+1), one gamete has one less chromosome (n-1)
  • abnormal gametes: 50%
62
Q

what are some examples of non-disjunction

A
  • down syndrome: 21 trisomy
  • turner syndrome: X chromosome monosomy
  • edward’s syndrome: trisomy 18
63
Q

what are the two types of chromosomal abnormalities

A
  • abnormal chromosome number
  • abnormal chromosome structure
64
Q

what is aneuploidy

A
  • non disjuction occurs leading to a cell which is trisomy (n+1) or monosomy (n-1)
  • most situations are lethal in humans
65
Q

what is polyploidy

A
  • a zygote produced by fertilization of a haploid gamete with a diploid cell producing a cell with more than 2 sets of chromosomes
66
Q

what can cause abnormal chromosome structure

A
  • deletion
  • translocation
  • duplication
  • inversion
67
Q

when can abnormal chromosome structure happen

A
  • crossing over when genetic material that is exchanged doesn’t reattach properly
  • mistakes during DNA replication
68
Q

what happens in deletion

A
  • detached fragment of DNA does not get reattached and is lost
  • example: Wolf-Hirschhorn syndrome
69
Q

what happens in translocation

A
  • detached segment of DNA reattaches to a non - homologous chromosome
70
Q

what happens in duplication

A
  • a segment of DNA is duplicated during DNA replication
71
Q

what happens in duplication during crossing over

A
  • results in one chromosome becoming longer while the other is shorter
  • longer chromosome will have a duplicated section
  • shorter chromosome will have a deletion
72
Q

what happens in inversion

A
  • detached fragment reverses its orientation and reattaches to the original chromosome

Grade 11 bio (16 decks)

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