9) Hunchback serves as a silencer protein for the gene encoding Ultrabithorax. A

Question

9) Hunchback serves as a silencer protein for the gene encoding Ultrabithorax. A) Which of these two genes is epistatic to the other? B) How do you know?

Hunch beck has (hb) gene and Ultrabithorax has (Ubx) gene.

hb is the epistatic gene, which suppresses the effect of Ubx; Hunchback is epistatic to Ultrabithorax. Is this correct and why?

Don’t understand how do you know this? Can a Punnett square be done to figure this out? What work can I show for how do you know this? I have asked this several times and received an explanation copy from the internet, which I did not understand when I looked it up. Can you please explain in simple terms and can a Punnett square show how to do this? Thank you

Explanation / Answer

A. Hunchback or hb gene is epistatic to ultrabithorax or ubx gene because

Hunchback is a segmentation gene, determines the head and thorax structures. Hunchback or hb gene code transcription factors that control the expression of further embryonic genes eg pair rule genes and homeotic genes. Thats why it acts as epistatic to ubx gene.

B. Ultrabithorax is a homeotic gene that specify the development of posterior portion. Hb gene binding sites are present on ubx control regions which cause direct repression or silencing of the homeotic gene ultrabithorax. The silencing or repressing function of hb gene is determined by the ubx promoter.

Punnett square can not show how to do this.

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