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MCB1 Block 4 > Sex Chromosomes > Flashcards

Sex Chromosomes Flashcards

1
Q

What does PAR stand for

A

pseudoautosomal region

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2
Q

The X and Y chromosomes do what during meiosis

A

pair and segregate

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3
Q

what is the pseudoautosomal region?

A

regions b/w X and Y that allow them to pair during meiosis

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4
Q

what is the important PAR region in X and Y chrom

A

PAR1

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5
Q

what is the only location crossing over occurs in in x and Y chromosomes

A

Pseudoutosomal region - PAR1

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6
Q

how many copies of PAR1 genes do males have

A

2 - because it’s on both X and Y chromosome

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7
Q

how many copies of PAR1 genes do females have

A

2 copies but on one X chromosome it is inactivated

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8
Q

the genes in pseudoautosomal region behave in what way

A

as if they are autosomes b/c they are on both the X and Y chromsoome

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9
Q

What is SRY

A

sex determining gene - determines male sex development

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10
Q

Where is SRY located

A

very close to PAR1 region

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11
Q

what gene is deleted in azoospermia

A

AZF

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12
Q

If SRY why is present what will happen

A

male sexual development

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13
Q

What is testes determining factor

A

SRY

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14
Q

If you are 46, XX with SRY what will happen

A

phenotypically male

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15
Q

If SRY has recombination what happens

A

The X chromosome would have SRY and present phenotypically as males or the Y will not have SRY and will present phenotypically as females

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16
Q

Are 46, XX with SRY + be fretil

A

No, missing other genes for spermatogenesis

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17
Q

46, XY SRY- are what

A

phenotypcically female

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18
Q

are 46, XY SRY- fertile?

A

no

need both copies of X chromosome for normal oocyte development

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19
Q

What is the master regulating gene for female developmen

A

WNT4

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20
Q

What does WNT4 activate to specify ovarian development

A

DAX1

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21
Q

What does SRY acticate

A

SOX9

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22
Q

What does SOX9 activate

A

SF1 and other genes

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23
Q

What does SOX9 inhibit

A

WNT4 development

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24
Q

What does DAX1 inhibit

A

SOX9

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25
Q

What does SF1 and other genes do

A

testes develop

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26
Q

Once ovaries develop, what is produced

A

estradiol

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27
Q

what does estradiol signal for development

A

external female genitalia

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28
Q

what do mullerian ducts form

A

internal female genitalia

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29
Q

Once testes are present what androgen is synthesized

A

testosterone

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30
Q

what does testosterone initiate development of

A

external male genitalia & with wolifan ducts the internal male genitalia

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31
Q

Dihydrotestosterone is what

A

more potent than testosterone

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32
Q

testosterone with 5 alpha reductase makes what

A

dihydrotestosterone

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33
Q

What does dihydortestosterone do regarding testes

A

accelerates development of testes

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34
Q

What happens if androgen signaling is not working properly

A

Androgen insensitivity syndrome

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35
Q

androgens are what

A

steroid hormones

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36
Q

what hormone does testes produce besides testosterone

A

MIF - mullerian inhibitory factor

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37
Q

In the absence of AR what pathway will stay active

A

MIF pathway

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38
Q

What does AR stand for

A

Androgen receptor

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39
Q

In absence of AR what happens phenotypically

A

may be external female genitalia but will not be functional

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40
Q

An individual with null mutation in SRY gene would be expected to appear as a:

A

infertile female

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41
Q

DSD stands for what

A

Disorders of sex development

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42
Q

what is male pseudohermapharoditism now called

A

XY DSD

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43
Q

What is female pseudohermaphroditism now called

A

XX DSD

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44
Q

If there is SOX9 loss of function what happens

A

testicular development won’t occur, no inhition of female part

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45
Q

What happens if there is SOX9 loss of function or DAX1 gain of function

A

46 XY sex reversal ,intersex or gonadal dysgenesis is common

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46
Q

What happens if there is DAX1 loss of function or SOX9 gain of function

A

46, XX sex reversal, intersex or gonadal dysgensis is common

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47
Q

DAX1 loss of function is another form of what

A

X-linked form of congenital adrenal hyperplasia

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48
Q

very generally what happens so SOX9/DAX1 gain of function

A

allelic heterogeneity, enhancer mutations, or the usual explanations for variable expressivity: the effect of modifier genes or stochastic events.

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49
Q

what is hermaphroditism

A

gonads change

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50
Q

what is pseudohermatphrotisism

A

gonds are what they should be, external genitalia is different

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51
Q

What causes Androgen insensitivey syndrome

A

mutations in Androgen Receptor Gene

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52
Q

What does AR gene stand for

A

androgen receptor gene

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53
Q

What does AIS stand for

A

androgen insensitivity syndrome

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54
Q

AIS is also known as what

A

XY DSD

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55
Q

XY DSD was formerly called what

A

male pseudohermaphroditism

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56
Q

What is MOI of AIS

A

X-linked recessive

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57
Q

how is AIS X-linked recessive

A

rare transcription factor mutation resulting in recessive inheritance

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58
Q

If pt is 46 XY with AIS what happens

A

feminization of male genitalia
undermasculinized to ambiguous to complete sex reversal
femal secondary sexual phenotypes
testes develop (why it’s pseudohermaphroditism) ,inferfility
no ovaries or uterus

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59
Q

If pt is 46, XX with AIS what happens

A

heterozygous carriers

minimally affected

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60
Q

Why are females not reallyk affeted with AIS

A

females do’nt really use androgens

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61
Q

What is most severe form of AIS

A

complete androgen insensitivey syndrome (CAIS)

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62
Q

What does CAIS stand for

A

Complete androgen insensitivyt syndrome

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63
Q

What is intermediate AIS

A

Partial androgen insensitivy syndrome( PAID)

64
Q

what is mild form of AIS

A

mild androgen insensitivity syndrome (MAIS)

65
Q

Severe
Female genitalia & secondary sex characteristic
Often present as teenagers due to amenorrhea
is what?

A

CAIS

66
Q

Intermediate
Variable, predominant male, female or ambiguous genitalia
is what?

A

PAIS

67
Q

Mild
Male genitalia with possible undermasculinization, infertility
is what?

A

MAIS

68
Q

androgen receptor gene has what repeat

A

CAG & GGN

69
Q

In GGN repeat in exon 1 of androgen receptor gene what can the repeated nucleotide be?

A

anything except A

70
Q

GGN repeat leads to what aa

A

glycine

71
Q

variation in GGN repeat is associated with what

A

male patterned baldness

72
Q

CAG repeat in AR gene can lead to what

A

loss of function of androgen receptor

73
Q

complete loss of funciton of AR gene is what

A

AIS

74
Q

partial loss of function of AR gene is what

A

male pseudohermaphroditism

75
Q

What is dosage compensation

A

in females, one of the x chromosomes is inactivated which balances what is expessed on x chromosome b/w male and females - so males and females express same amount of gene product

76
Q

What do mammals always use for dosage compensation

A

X inactivation

77
Q

What is another term for x chromosome inactivation

A

lyoniztion

78
Q

what is lyonization onw called

A

the lyon law

79
Q

when is x chromosome inactive in males

A

in males during spermatogonia

80
Q

before primordial germ cell can go into meiosis what has to happen with X chromosomes

A

the inactive x chromosome needs to be reactivated

81
Q

when will female have both x chromosomes active

A

during meiosis

82
Q

will zygote have two active x chromosomes

A

yes

83
Q

when does blastocyst inactive x chromosome

A

week 1

84
Q

which x chromosome will be inactive in fetus

A

random

85
Q

about half of the cells in female adult will have 1/2 what and 1/2 what regarding X chromosome

A

1/2 maternal X chromosome

1/2 paternal X chromosome

86
Q

how are females mosaics

A

they have 1/2 paternal and 1/2 maternal X expresed in their cells

87
Q

Androgen receptor is a what

A

transcription factor

88
Q

If there is 70:30 of paternal/maternal X chromosomes activated is that normal

A

yes

89
Q

what do inactive chromosomes do to not be expressed

A

condensed into heterochromatin

90
Q

What does inactive x chromosome look like under microscope

A

Barr body

91
Q

Even though 1 X chromosome is inactivated, what is not?

A

PAR1 region - it is still expressed in inactive chromosome

92
Q

Besides PAR1 region what else stays active in inactive X chromosome

A

10-15% of chromosome ia active

another 10% if variably active

93
Q

What is X inacrivation contorlled by

A

X inactivation center

94
Q

what does XIC stand for

A

X inactivation Center

95
Q

XIC contains what important gene

A

XIST gene

96
Q

what gene controls X inactivation

A

XIST gene

97
Q

What does XIST stand for

A

X inactivation specific transcript

98
Q

what is strange about evolutionary conservation in XIST

A

it has low evolutionary conservation w/b different species

99
Q

XIST is a functional:

A

RNA molecule

100
Q

Does XIST have an open reading frame

A

no - it doesnt make protein

101
Q

Is XIST protein coding

A

no - it is a functional RNA

102
Q

XIST is expressed from which chromosomes

A

both but mainly the inactive one

103
Q

where is XIST expressed on active X

A

pinpoint of it

104
Q

XIST does what to inactive X

A

coats it and induces chromatin condensation thereofre gene silencing

105
Q

at what stage does XIST RNA increase dramatically

A

late blastocyst stage when X chromosomes need to be randomly inactivated

106
Q

silencing of X chromosome can be blocked by what

A

antisense RNA

107
Q

If Xis is overproduced what can happen

A

it can spread to autosomal sequences and even silence genes in male

108
Q

blocking factor is expressed from what

A

autosome NOT sex chromosome

109
Q

how does blockin factor ensure only one X chromosome will be inactive

A

there is only enough produced to bind to one X chromosome

110
Q

Where does blocking factor bind to X chromosome

A

near Xist gene

111
Q

the x chromosome that is bound by blocking factor is

A

active

112
Q

why is the x chromosome that is bound by blocking factor active

A

it binds to Xist which stops it from spreading and inactivating the chromosome

113
Q

how does blockin protein allow activation

A

stops Xist gene from spreading which would cause inactivation. It binds near xist gene

114
Q

histone acetylation is associated with what

A

open chromatin

a = active

115
Q

histone methylation is associated with what

A

heterochromatin

116
Q

What does blocking factor do

A

binds to presumptive active X

117
Q

What is nonrandom (skewed) X inactivation

A

one of the X chromosomes being preferetially activated it’s outside of 70:30 ratio

118
Q

Even in Nonrandom/skewed X inactivation, what is happening

A

they are still being randomly activated, it just happens that one of them is more activated than another
skewed is better nerve

119
Q

X activation is always

A

random

120
Q

what can lead to the skewing of X inactivation

A

If one of the X chromosomes carry a mutation then the cell may die which leads to advantage of one of the X chromosomes being active, and against the other X chromosome being active

121
Q

If X chromosome and autosome has translocation describe what happens

A

severe imbalance, part of X is being expressed that shouldn’t be, part of autosome is not being expressed that should be. the cell is not viable so will die.

122
Q

describe nonrandom X inactivation in female DMD

A

All genes are expressed in right proportions but there is not functional dystrophin gene expressed
The case where the functional dystrophin gene would be activated ,there is not equal translocation being expressed, part of the X was translocated to a autoaomse so there is extra X being expressed, cell dies

123
Q

What does SCID stand for

A

severe combined immunodeficiency

124
Q

what are the two forms of SCID

A

ADA Deficiency

X-linked SCID

125
Q

Desribe ADA deficiency

A

deficiency of adenosine deaminase

126
Q

Describe X-linked SCID

A

Deficiency of IL2RG

127
Q

Describe how ADA deficiency and X-linked SCID are related

A

both do not have functional lymphocytes, so they don’t have functional immune system. any little illness is very dangerous for them.

128
Q

What is MOI for ADA deficiency

A

AR

129
Q

What is MOI for X-linked SCID

A

X-linked recessive

130
Q

Describe the X-linked skewing you could expect to see in cases like X-linked SCID

A

mutant X chromosome is inactive in most cell types

131
Q

What is one way you can look at the inactive vs. active X chromosome when comparing through PCR tests

A

if it is methylated it is inactive (heterochromatin) so look at the methylation

132
Q

What SHOULD you see regarding peaks when looking at X chromosome for activation

A

Should see two smaller peaks b/c half of them should be active in each cell

133
Q

The X chromosome carrying the mutation will be preferentially

A

inactivated

134
Q

What does it mean if you only see one peak when looking at PCR digested with HpaII

A

one peak means that only one chromsomoe is activated - this means there is mutation in the inactive one. The inactive one is what you see when you digest with HpaII

135
Q

What does undigested DNA look at on PCR for alleles

A

what alleles they have, not whether something is active or inactive

136
Q

What does ATRX stand for

A

Alpha thalassemia with mental retardation

137
Q

Where has mutation in ATRX

A

ATRX gene

138
Q

What does ATRX gene encode

A

SWI2/SNF protein

139
Q

What does SWI2/SNF protein do

A

chromatin remodelng - helicase that determines chromatin structure and regulates gene expression

140
Q

Do female carriers of hemophelia have skewed activation?

A

no

141
Q

What doe CFNS stand for

A

craniofrontonasal syndrome

142
Q

What is MOI of CFNS

A

X-linked dominant

143
Q

Where is mutation in CFNS

A

EFNB1

144
Q

what does EFNB1 encode

A

Ephrin B1

145
Q

severe hyperelorism, coronal synostosis, grooved tip of nose, longitudinal nail split is what disease

A

CFNS

146
Q

Which chromosome is the mutation on in ATRX

A

active X chromsome (this is exception, usually it’s on the inactive)

147
Q

What protein is affected in CFNS

A

Ephrin B1

148
Q

What does defect in Ephrin B1 cause

A

defect in boundaries

149
Q

Why are males with CFNS less severe phenotypically than females

A

They still have boundaries b/c there is no Ephrin B1 expressed at all, so other things make up. So the boundary isn’t perfect but there is still a boundary. In females there is some expression of Ephrin B1, trying to use one signaling pathway, other cells using another signaling pathway, boundary forms incorrectly giving severe phenotype

150
Q

What is MOI of Rett Syndrome

A

X-linked dominant

151
Q

What gender does Rett Syndrome afect

A

females - affects males so severley they don’t survive

152
Q

What gene is mtuated in Rett Syndrome

A

MEPC2

153
Q

What does MEPC2 encode?

A

MePC2

154
Q

What does MePC2 stand for

A

Methyl CpG-binding protein 2

155
Q

Why are females and not males affect in X-linked Rett Syndrome

A

males are so severely affected they die

156
Q

symptoms: profound mental retardation in females, early onset, characteristic hand-wringing, progressive microcephaly, some have seizures is what disease

A

rett syndrome

MCB1 Block 4 (17 decks)

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