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genetics > ch. 3 meiosis > Flashcards

ch. 3 meiosis Flashcards

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Biology 101 flashcards
1
Q

is meiosis a cycle?

A

no

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2
Q

what does meiosis produce?

A

4 haploid cells (gametes)

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3
Q

where does mitosis occur

A

somatic cells

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4
Q

where does meiosis occur

A

germ-line cells

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5
Q

overview of meiosis 1

A
  • homologous chromosomes separate
  • centromeres don’t split
  • reduces diploid # to haploid #
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6
Q

overview of meiosis 2

A
  • sister chromatids separate
  • centromeres split
  • 4 haploid gametes
  • each gamete has one chromosome from the original diploid set of homologous chromosomes
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7
Q

mechanisms of diversity in meiosis 1

A
  • homologous chromosome pairing
  • crossing over between homologous chromosomes
  • segregation (separation) of homologous chromosomes (reduces chromosomes to haploid #)
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8
Q

stages of meiosis 1

A
  1. prophase 1
  2. metaphase 1
  3. anaphase 1
  4. telophase 1
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9
Q

five substages of prophase 1

A
  1. leptotene
  2. zygotene
  3. pachytene
  4. diplotene
  5. diakinesis
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10
Q

where does pairing and recombination of homologs take place

A

prophase 1

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11
Q

leptotene

A
  • chromosome condensation begins
  • centrosomes begin to migrate toward opposite poles
  • meiotic spindle forms as microtubules extend from centrosomes
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12
Q

zygotene

A
  • nuclear envelope disintegrates
  • homologous chromosomes undergo synapsis
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13
Q

synaptonemal complex (protein bridge_

A

tri-layer protein structure that binds non-sister chromatids of homologous chromosomes together
- forms between homologous chromosomes as they align

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14
Q

non-sister chromatids

A

belong to different members of a homologous pair

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15
Q

pachytene

A
  • chromosome condensation continues
  • tetrads form
  • crossing over begins (recombination nodules form)
  • kinetochore microtubules attach to kinetochores
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16
Q

tetrads

A

paired homologs
- all 4 chromatids visible

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17
Q

recombination nodules

A

aggregates of enzymes and proteins needed for crossing over between homologs
- form at intervals in synaptonemal complex

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18
Q

diplotene

A
  • crossing over completes
  • synaptonemal complex begins to dissolve
  • chiasma
  • nucelar envelope breakdown finishes
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19
Q

chiasma

A

locations where crossing over has occured

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20
Q

what is present between sister chromatids?

A

cohesin protein

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21
Q

what does cohesin resist

A

resists pulling forces of kinetochore microtubules

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22
Q

do centromeres split during meiosis 1?

A

no

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23
Q

diakinesis

A
  • kinetochore microtubules move synapsed chromosome pairs toward metaphase plate
  • homologs align side by side
  • centromeres remain intact
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24
Q

metaphase 1

A
  • chiasmata between homologs resolved, completes crossing over
  • homologs align on opposite sides of metaphase plate
  • kinetochore microtubules attach to both sister. chromatids of one homolog pair
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25
Q

anaphase 1

A
  • homologs separate from one another and are pulled to opposite poles of cell
  • movement caused by shortening of kinetochore microtubules
  • sister chromatids remain attached by cohesin
  • centromeres remain intact
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26
Q

telophase 1

A
  • nuclear membranes briefly reform around haploid sets of chromosomes
  • followed by cytokinesis
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27
Q

cytokinesis in meiosis

A
  • divides cytoplasm to create 2 haploid cells (n+n)
  • each cell carries 2 copies of each haploid set
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28
Q

why is meiosis I called reductional division

A

because the policy of the daughter cells is halved compared to the original diploid parent cell
- still 2 copies of each genome

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29
Q

meiosis 2 is similar to…

A

mitosis in a haploid cell

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30
Q

what does meiosis 2 divide each haploid daughter cell into

A

2 haploid cells by separating sister chromatids from one another

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31
Q

what is the independent assortment of alleles illustrated by

A

behavior of 2 pairs of homologues during meiosis

32
Q

for an organism with genotype AaBb, 2 equally likely arrangements of paired homologs can occur:

A
  • gametes AB and ab
  • games Ab and aB
33
Q

sex determination

A

involves genetic and biological processes that produce the male and female characteristics of a species

34
Q

chromosomal sex

A

presence of chromosomes characteristic of each sex and is determined at the moment of fertilization

35
Q

phenotypic sex

A

internal and external morphology of each sex, and results from differences in gene expression

36
Q

what chromosomes do placental mammals have

A

X and Y

37
Q

male mammals

A

XY (normal), XXY, or XYY

38
Q

female mammals

A

XX (normal), XO, or XXX

39
Q

pseudoautosomal regions (PAR1 and PAR2)

A

two small regions of homology that exist between the X and Y chromosomes

40
Q

what do PAR1 and PAR2 allow?

A

homologous pairing between X and Y and meiosis
- there is evidence that crossing over occurs within this regions

41
Q

undifferentiated gonads

A

clusters of tissue in early mammalian embryos that can develop as ovaries or testes

42
Q

what does sex determination depend on

A

presence of absence of single gene, SRY, found on Y chromosome

43
Q

SRY

A

transcription factor needed for male-specific gene expression

44
Q

what does the expression of SRY initiate

A

testicular development of undifferentiated gonads

45
Q

what does absence of SRY result in

A

allows default, female state to develop

46
Q

sex determination for birds, some reptiles, some fish, butterflies, and moths

A

Z/W system
- females: 2 different sex chromosomes (ZW)
- males: 2 same sex chromosomes (ZZ)

47
Q

sex chromosomes of platypus

A

5 pairs of sex chromosomes:
- 5 XY pairs in males
- 5 XX pairs in females

48
Q

sex determination in Drosophila

A
  • females: 2 X chromosomes (XXY, XX)
  • males: 1 X chromosome (X0, XYY, XY)
49
Q

what does the dosage of the X chromosome determine in Drosophila

A

outcome of a sex determination gene regulation cascade

50
Q

X/A ratio (X:autosome)

A

determines gender based on number of X chromosomes to sets of autosomes
- males: 0.5
- females: 1.0

51
Q

dosage compensation

A

any mechanism that compensates for the difference in number of copies of genes between males and females

52
Q

how many mechanisms of dosage compensation

A

4

53
Q

what happens early in mammalian development to 1 of X chromosomes

A

randomly inactivated

54
Q

Lyon hypothesis

A

random X inactivation hypothesis named after Mary Lyon (1962)

55
Q

Barr body

A

inactive condensed X chromosome visible near nuclear wall

56
Q

once X inactivation has occurred in a cell…

A

it is permanent in al the descendants of that cell

57
Q

how can some female mammals be mosaics of 2 populations of cells

A

one cell expresses maternal X, other paternal X

58
Q

what does the X chromosome carry a gene for in cats

A

coat color

59
Q

tortoiseshell cats and mosaicism

A

random X inactivation in heterozygous females leads to pattern of orange/black patches unique to each ind.

60
Q

random X inactivation requires what?

A

X-linked gene called Xist (X-inactivation-specific-transcript)

61
Q

what does the Xist gene do

A
  • produces large RNA moelcules that spread out and cover/pain chromosome to be inactivated
62
Q

what can Xist only act on

A

the chromosome from which it is being transcribed, not the homolog

63
Q

do all genes on the inactivate X undergo inactivation?

A

no, some escape

64
Q

X-linked recessive inheritance

A

females homozygous for recessive allele or males homozygous for it display recessive phenotype

65
Q

hemizygous

A

when only one copy is present

66
Q

hemizygous males

A

display any allele on their single X whether the allele is recessive or dominant in females

67
Q

X-linked dominant traits

A

heterozygous females and hemizygous males for dom allele express the dominant phenotype

68
Q

hallmark of recessive X-linked inheritance

A

expression of trait much more often in males than females

69
Q

do more males or females have X-linked recessive trait

A

males due to hemizygosity

70
Q

hemophilia A

A

X-linked recessive trait caused by mutation in factor VIII gene on X chromosome

71
Q

what does the mutant allele of hemophilia A produce

A

nonfunctional blood-clotting protein

72
Q

frequency in sexes of X-linked dominant traits

A

appears relatively equally in males and females

73
Q

congenital hypertrichosis (CGH)

A

rare X-linked dominant disorder in humans that leads to large increased in number of hair follicles on body

74
Q

Y-linked trait transmission

A

exclusively male-to-male pattern

75
Q

how many genes on Y chromosome in males

A

fewer than 50

76
Q

do genes on the Y chromosome have a copy on the X chromosome?

A

no

genetics (47 decks)

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