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Gene regulation > Sex determination in mammals and drosophila 2 > Flashcards

Sex determination in mammals and drosophila 2 Flashcards

1
Q

What is the first step in x inactivation?

A

Xist initiates gene silencing

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2
Q

Which enzyme does Xist activate?

A

Histone deacetylase

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3
Q

What is the effect of removing acetyl groups from histones?

A

Reduced translation

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4
Q

What happens in X inactivation after activation of histone deacetylase?

A

Polycomb protein activated

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5
Q

How is polycomb protein involved in X inactivation?

A

Xist binds to the polycomb repressor complex and causes methylation of H3K27

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6
Q

What is the third stage of X inactivation?

A

DNA methylation on CPG islands by DNA methyltransferase

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7
Q

How does a cell count the number of X chromosomes it has?

A

RNF12 targets REX1 TF. REX1 inhibits Xist. More RNF12=more Xist. RNF12 is on X chromosome so more RNF12=more X inactivation

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8
Q

What happens upon ectopic RNF12 expression?

A

Xist is expressed in male cells

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9
Q

What sex do XX flies develop into?

A

Females

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10
Q

What sex do XY flies develop in?

A

males

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11
Q

Main observable difference between female and male drosophila?

A

Males have a dark tip at the end of the abdomen

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12
Q

What sex do XO flies develop into?

A

Males, but they are sterile

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13
Q

Which sex chromosome pair shows a difference in phenotypic sex between humans and drosophila?

A

XO (human female, drosophila male) and XXY (human male, drosophila female)

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14
Q

What determines sex in drosophila?

A

The ratio of X chromosomes to autosomes

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15
Q

What is the sex of a drosophila organism that has X:AA (0.5)?

A

Male

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16
Q

What is the sex of a drosophila organism that has XX:AA (1)?

A

Female

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17
Q

What is the sex of a drosophila organism that has XX:AAA (0.66)?

A

It will develop with both male and female characteristics–> intersex

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18
Q

What are gynandromorphs?

A

Animals composed partly of XX cells and partly of XO cells

19
Q

How are gynandromorphs generated?

A

XX embryos that loses one of the X chromosomes early in embryogenesis–> the organism is half XX and half XO if the loss occurs at the first division

20
Q

Difference in sex determination between mammals and drosophila?

A

In mammals the sex based differentiation depends upon hormones secreted by gonads, in the fly the sex based differentiation depend on the chromosomal sex of the cells that differentiate

21
Q

What is the Sxl (sex lethal) gene required for in drosophila?

A

Female development

22
Q

What happens to a female fly that has a loss of function mutation in the Sxl gene?

A

It is lethal but only to the female

23
Q

What type of mutations in the Sxl gene are lethal to males?

A

Gain of function mutations

24
Q

In what state must the Sxl gene be to promote male development?

A

Inactive

25
Q

In what state must the Sxl gene be to promote female development?

A

Active

26
Q

What female specific effect does mutations in sisterless-a and sisterless-b have?

A

They are lethal

27
Q

What do the sisterless genes encode?

A

Basic helix-loop-helix (bHLH) proteins

28
Q

What type of protein (their role) are bHLH proteins?

A

TFs, DNA binding motifs

29
Q

Which chromosomes has the sis-a and sis-b genes?

A

X-chromosome

30
Q

How much sis-a and sis-b protein do XX cells make compared to XY or XO cells?

A

Twice as much

31
Q

What happens if sis proteins homodimerises?

A

It can bind DNA and act as a TF

32
Q

What is a target of a sis protein homodimer?

A

Sxl, activating Sx

33
Q

What happens if a sis protein heterodimerises with an autosomal bHLH?

A

They result in inactive complexes

34
Q

Why are sis proteins more likely to form homodimers in XX individuals?

A

There is a higher ratio of sis bHLH proteins to autosomal bHLH proteins

35
Q

What happens if more sis bHLH homodimers form?

A

The Sxl gene is turned on, so that cell is female

36
Q

What process does the Sxl gene regulate?

A

Splicing of mRNA

37
Q

What is the RRM type proteins that Sxl contains?

A

RNA binding proteins

38
Q

Which sequences does Sxl recognise?

A

Sequences with long Poly U stretches interrupter by guanosines

39
Q

Where are the Sxl recognition sequences located?

A

In introns flanking the third exon

40
Q

What specifically does Sxl bind to?

A

SPF45

41
Q

What effect does Sxl binding have on SPF45?

A

SPF45 is inactivated

42
Q

What effect does Sxl have on mature mRNA formation?

A

Exon 2 is fused with Exon 4 instead of exon 3 being in the middle–> female development

43
Q
A

Gene regulation (12 decks)

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