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genetics > chapter 3 part 2 (meiosis) > Flashcards

chapter 3 part 2 (meiosis) Flashcards

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1
Q

is meiosis a cycle?

A

no

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2
Q

what does meiosis produce?

A

gametes for sexual reproduction that are genetically different

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3
Q

what happens big picture in meiosis 1?

A

-homologous chromosomes separate
-centromeres DO NOT split
-reduces diploid number of chromosomes to the haploid number

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4
Q

what happens in meiosis ii big picture?

A

-sister chromatids separate
-centromeres split
-produce four haploid gametes
-each gamete has one chromosome from the original diploid set of homologous chromosomes

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5
Q

what is unique to meiosis?

A

homologous chromosome pairing
crossing over between homologous chromosomes

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6
Q

what happens when we segregate the homologous chromosomes?

A

the chromosomes are reduced to the haploid number (n)

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7
Q

what are the means of generating genetic diversity by sexual reproduction?

A

crossing over between homologous chromosomes
segregation of homologous chromosomes

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8
Q

stages of meiosis I

A

-prophase 1
-metaphase 1
-anaphase 1
-telophase 1

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9
Q

when does pairing & recombination of homologous chromosomes take place?

A

in prophase 1

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10
Q

what are the 5 stages of prophase 1?

A
  1. leptotene
  2. zygotene
  3. pachytene
  4. diplotene
  5. diakinesis
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11
Q

when does chromosome condensation begin?

A

leptotene

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12
Q

leptotene & zygotene

A

-chromosome condensation begins in leptotene
-meiotic spindle forms as microtubules extend out from centrosomes
-nuclear envelope disintegrates during zygotene
-homologous chromosomes undergo synapsis

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13
Q

when does nuclear envelope disentegrate?

A

during zygotene

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14
Q

what is the synaptonemal complex?

A

-forms between homologous chromosomes as they align
-tri-layer protein structure binds to non-sister chromatids (of homologous chromosomes) together
-non-sister chromatids belong to different members of a homologous pair

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15
Q

where does chromosome condensation continue?

A

in pachytene

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16
Q

what are paired homologs called?

A

tedtrads (all 4 chromatids are visible)
-this is in pachytene

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17
Q

where do recombination nodules form?

A

in the synaptonemal complex

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18
Q

what are recombination nodules?

A

aggregates of enzymes & proteins needed for crossing over between homologs

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19
Q

where do chromosomes even further condense?

A

in diplotene- then the synaponemal complex behins to dissolve

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20
Q

when homologs slightly pull apart in finalizing crossing over, what is revealed at locations where crossing over has occured?

A

chiasma

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21
Q

what protein is present between sister chromatids?

A

cohesin

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22
Q

what does cohesin do?

A

resists the pulling force of kinetechore microtubules

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23
Q

do centromeres split in meiosis 1?

A

NO

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24
Q

what happens in diakinesis?

A

kinetochore microtubules move synapsed chromosome pairs toward the metaphase plate
-homologs align side by side.
CENTROMERES REMAIN INTACT

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25
Q

by metaphase 1, what has happened?

A

chiasmata between homologs are resolved, which completes crossing over

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26
Q

what happens in metaphase 1

A

-homologs align on opposite sides of the metaphase plate (different arrangement than what happens suring mitosis)
-kinetochore microtubules attach to both sister chromatids of one homolog pair (kinetochore microtubules from the opposite pole do the same for the other homolog)

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27
Q

what occurs in anaphase 1?

A

-sister chromatids remain firmly attached by cohesion
CENTROMERES REMAIN INTACT

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28
Q

when does anaphase 1 begin?

A

-when homologs separate from one another & are pulled to opposite poles of the cell (movement caused by shortening of kinetochore microtubules)

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29
Q

what occurs in telophase 1?

A

the nuclear membranes briefly reform around the separated haploid sets of chromosomes

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30
Q

what follows telophase 1 & what happens?

A

cytokinesis, it divides the cytoplasm to create two haploid cells (n=n)
-each cell carries two copies of each haploid set (sister chromatids)
-diversity of information has been reduced !!!!!!

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31
Q

Meiosis I is called the ________ _________ because the ploidy of the daughter cells is _______ compared to the original diploid parent cell

A

reductional division
halved

-but there are still two copies of each genome

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32
Q

what does meisos II divide each haploid daughter cell into?

A

two haploid cells, by separating sister chromatids from one another

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33
Q

what is meisos II similar to?

A

mitosis in a haploid cell

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34
Q

what is produced in meisos II?

A

four genetically distinct haploid cells, each carrying one chromosome from a homologous pair

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35
Q

what is the major means of generating genetic diversity?

A

independent assortment

36
Q

what is the independent assortment of alleles illustrated by?

A

behavior of two pairs of homologues during meiosis

37
Q

for an organism with genotype AaBb, how many arrangements can occur, what are they, and what is the likelihood of each?

A

2
AB and ab
Ab and aB
-they are all equally likely to occur

38
Q

what does sex determination involve?

A

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

39
Q

what is chromosomal sex

A

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

40
Q

what is phenotypic sex?

A

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

41
Q

what type of chromosomes do placental mammals have?

A

X & Y chromosomes

42
Q

mammal female chromosomes

A

normal: XX
XO or XXX

43
Q

mammal male chromosomes

A

normal: XY
XXY or XYY

44
Q

psuedoautosomal regions

A

(PAR1 & PAR2)
exist between X & Y chromosomes

45
Q

what allows homologous pairing between X & Y at meisosis

A

psuedoautosomal regions

-also evidence that crossing over occurs within these regions during meiosis

46
Q

what in the mammal can either develop as testes or ovaries?

A

undifferentiated gonads
-(are clusters of tissue in mammalian embryos)

47
Q

what is SRY?

A

a transcription factor needed for male specific gene expression

48
Q

what is the single gene that its absence or presence determines the sex?

A

SRY, found on the Y chromosome

49
Q

what does expression of SRY initiate?

A

testicular development of undifferentiated gonads

50
Q

what does the absence of SRY allow?

A

the ‘default’ female state to develop

51
Q

what chromosomal system do birds, some reptiles, some fish, & moths use?

A

the Z/Y system

52
Q

in the systems that birds, some reptiles, some fish, & moths use, what makes up a female?

A

ZW (two different sex chromosomes)

53
Q

in the systems that birds, some reptiles, some fish, & moths use, what makes up a male?

A

ZZ (same two sex chromosomes)

54
Q

how many pairs of sex chromosomes do platypuses have?

A

5 XY pairs in males
5 XX pairs in females

55
Q

drosophila female chromosomes

A

XXY or XX (normal)

56
Q

drosophila male chromosomes

A

X0, XYY or XY (normal)

57
Q

what ratio do male dropshila have?

A

X/A ration of 0.5

58
Q

what ratio do female drosophila have?

A

1.0

59
Q

what determines the outome of a sex determination gene regulation is drosophila?

A

the dosage of the X chromosome

60
Q

how many different mechanisms of dosage are there?

A

4

61
Q

Any mechanism that compensates for the difference in number of copies of genes between males and females is called

A

dosage compensation

62
Q

what is the random X inactivation process also called?

A

the Lyon hypothesis

63
Q

in mammalian development, what is randomly inactivated?

A

one of the two X Chromosomes

64
Q

what is condensed as a Barr Body?

A

the inactive X chromosome that is visible near the nuclear wall

65
Q

once X inactivation has occured in one cell, it is what

A

permanent in all the descendants of that cell

66
Q

in cats, the X chromosome carries a gene responsible for what?

A

coat color

67
Q

what does random x inactivation of heterozygous females lead to in cats?

A

a pattern of orange & black patches that is unique to each individual

68
Q

what does random X-inactivation require?

A

an x-linked gene called Xist

69
Q

what does Xist produce?

A

large molecules that spread out & cover (or paint) the chromosome to be inactivated

70
Q

Xist can only act on what?

A

on the chromosome from which it is being transcribed

71
Q

what sometimes escaped X inactivation

A

some genes on the inactive X

72
Q

what is something common/expected with recessive X-linked inheritance?

A

the expression of the trait much more often in males than females

73
Q

hemizygous

A

a diploid organsim is hemizygous when only one copy is present
the cell or organism is called a hemizygote
hemizygosity is also oberserved when one copy of a gene is deleted, or in the heterogametic sex when a gene is located on a sex chromosome

74
Q

hemizygous males

A

-they display any allele on their single X whether the allele is recessive of dominant in females

75
Q

who displays the recessive phenotype for X-linked recessive?

A

males hemizgyous for it or females homozygous for the recessive allele

76
Q

in X-linked dominant traits, who expresses the dominant phenotype

A

heterozygous females & hemizygous males for the dominant allele

77
Q

what does the mutant allele of hemphilia A produce?

A

a nonfunctional blood-clotting protein

78
Q

what is de-novo

A

newly occurring mutation

79
Q

what is hemophilia A caused by?

A

mutation in the factor VIII gene on the X chromosome

80
Q

how is hemophilia A inherited?

A

as an x-linked recessive trait

81
Q

for dominant x-linked traits it is equally likely for males & females to have it

A

true

82
Q

what type of disorder is congenital hypertrichosis?

A

a rare x-linked dominant disorder

83
Q

what does congenital hypertrichosis lead to??

A

large increase in the number of hair follicles on the body

84
Q

Y linked traits transmission

A

exclusively male-to-male

85
Q

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

A

no

genetics (23 decks)

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