1 Gene expression • Review sessions wt Jackie: 3-5PM Thursdays, room 8 Illick • Previous: www.esf.edu/efb/powell/Gen_L8_3.pdf www.esf.edu/efb/powell/Gen_L8_6.pdf www.esf.edu/efb/powell/Gen_L9_3.pdf www.esf.edu/efb/powell/Gen_L9_6.pdf www.esf.edu/efb/powell/Gen_L10_3.pdf www.esf.edu/efb/powell/Gen_L10_6.pdf Next Tuesday: www.esf.edu/efb/powell/Gen_L11_3.pdf www.esf.edu/efb/powell/Gen_L11_6.pdf Lac operon in E. coli • What if glucose and lactose are present? – Note: takes less resources to use glucose • Lac operon is not turned on • Catabolite Repression – A product of glucose catabolism inhibits the formation cAMP (cyclic adenosine monophosphate) – Increase glucose = decrease cAMP – Decrease glucose = increase cAMP Lac operon in E. coli • How does cAMP effect the Lac operon? • cAMP binds to a protein called CAP (catabolite activator protein) • cAMP/CAP increases binding of RNA polymerase to the Lac operon’s promoter, therefore increases expression • cAMP/CAP - example of positive control (required for activation)
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dsx-F protein dsx-M proteinRepression ofmale-specific genes
Repression offemale-specific genes
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Drosophila• Null mutation of Sxl?• Male• Null mutation of Tra?• Male• Therefore, male is default pathway• Null mutation of dsx• Characteristics of both male and female
– No suppression of genes
Female: X:A = 1 Male: X:A = 0.5
Sxl (on) Sxl (off)
tra (on) tra (off)
dsx mRNAfemale splice
dsx mRNAmale splice
dsx-F protein dsx-M protein
Repression ofmale-specific genes
Repression offemale-specific genes
Sex determination in mammals
Comparison: Drosophila MammalsX:A ratio
Sex determination in mammals
Comparison: Drosophila MammalsX:A ratio Y chromosome
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Sex determination in mammals
Comparison: Drosophila MammalsX:A ratio Y chromosome
autonomous non-autonomous every cell global
Sex determination in mammals
Comparison: Drosophila MammalsX:A ratio Y chromosomeautonomous non-autonomousevery cell global
mosaics: male and female male or female
Sex determination in mammals
Comparison: Drosophila MammalsX:A ratio Y chromosomeautonomous non-autonomousevery cell global
mosaics: male and female male or female
Why? - secondary sexual phenotypes are driven by the presence or absence of the testes
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Human development
• Gonads form within first two months fromconception
• If Y chromosome is present, then testes form• If no Y, then ovaries form• testes secrete testosterone (steroid hormone)• Testosterone binds to androgen-receptors in
all the cells of the body (global)• These act as transcription factors which
enhance male specific gene expression
Human development
• If no testosterone, androgen-receptors are notactivated, therefore female genes are expressed bydefault
• What would happen if a null mutation occurred in theandrogen-receptor gene?
• Testicular feminization (Tfm) syndrome– XY female– Female secondary characteristics, but has testes
instead of ovaries (demo. of global affect)• Several types of mutations that effect sex
determination
(Caster)
Human development
• Testosterone - developmentally specific for sometraits– developmental timing is important