Sex determination in mammals and drosophila 2

Question 1

What is the first step in x inactivation?

Answer 1

Xist initiates gene silencing

Question 2

Which enzyme does Xist activate?

Answer 2

Histone deacetylase

Question 3

What is the effect of removing acetyl groups from histones?

Answer 3

Reduced translation

Question 4

What happens in X inactivation after activation of histone deacetylase?

Answer 4

Polycomb protein activated

Question 5

How is polycomb protein involved in X inactivation?

Answer 5

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

Question 6

What is the third stage of X inactivation?

Answer 6

DNA methylation on CPG islands by DNA methyltransferase

Question 7

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

Answer 7

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

Question 8

What happens upon ectopic RNF12 expression?

Answer 8

Xist is expressed in male cells

Question 9

What sex do XX flies develop into?

Answer 9

Females

Question 10

What sex do XY flies develop in?

Answer 10

males

Question 11

Main observable difference between female and male drosophila?

Answer 11

Males have a dark tip at the end of the abdomen

Question 12

What sex do XO flies develop into?

Answer 12

Males, but they are sterile

Question 13

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

Answer 13

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

Question 14

What determines sex in drosophila?

Answer 14

The ratio of X chromosomes to autosomes

Question 15

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

Answer 15

Male

Question 16

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

Answer 16

Female

Question 17

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

Answer 17

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

Question 18

What are gynandromorphs?

Answer 18

Animals composed partly of XX cells and partly of XO cells

Question 19

How are gynandromorphs generated?

Answer 19

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

Question 20

Difference in sex determination between mammals and drosophila?

Answer 20

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

Question 21

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

Answer 21

Female development

Question 22

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

Answer 22

It is lethal but only to the female

Question 23

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

Answer 23

Gain of function mutations

Question 24

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

Answer 24

Inactive

Question 25

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

Answer 25

Active

Question 26

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

Answer 26

They are lethal

Question 27

What do the sisterless genes encode?

Answer 27

Basic helix-loop-helix (bHLH) proteins

Question 28

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

Answer 28

TFs, DNA binding motifs

Question 29

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

Answer 29

X-chromosome

Question 30

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

Answer 30

Twice as much

Question 31

What happens if sis proteins homodimerises?

Answer 31

It can bind DNA and act as a TF

Question 32

What is a target of a sis protein homodimer?

Answer 32

Sxl, activating Sx

Question 33

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

Answer 33

They result in inactive complexes

Question 34

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

Answer 34

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

Question 35

What happens if more sis bHLH homodimers form?

Answer 35

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

Question 36

What process does the Sxl gene regulate?

Answer 36

Splicing of mRNA

Question 37

What is the RRM type proteins that Sxl contains?

Answer 37

RNA binding proteins

Question 38

Which sequences does Sxl recognise?

Answer 38

Sequences with long Poly U stretches interrupter by guanosines

Question 39

Where are the Sxl recognition sequences located?

Answer 39

In introns flanking the third exon

Question 40

What specifically does Sxl bind to?

Answer 40

SPF45

Question 41

What effect does Sxl binding have on SPF45?

Answer 41

SPF45 is inactivated

Question 42

What effect does Sxl have on mature mRNA formation?

Answer 42

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