Intro

Question 1

What are HOM genes?

Answer 1

HOM gene are homeotic genes which regulate the development of anatomical structures in various organisms such as insects, mammals and plants.

Responsible for homeotic transformations.

Question 2

What is their role?

Answer 2

HOM-C genes in Drosophila specifiy PS identity

Question 3

What is a parasegment?

Answer 3

A parasegment is a transegmental unit of posterior compartment of one segment and the anterior compartment of the immediately posterior segment.

Question 4

Why are there segments and parasegments?

Answer 4

Expression patterns in early embryo are designated by PS boundaries so they are fundamental to embryonic gene expression - basic unit of embryonic construction. Segments are better used to describe the adult body plan.

Question 5

Describe the structure of the HOM-C (homeotic complex) in Drosophila

Answer 5

2 complexes on chromosome 3 separated by 9.6Mb

• Antennapedia complex (ANT-C)
• Bithorax complex (BX-C)

Question 6

What is the role of ANT-C?

Answer 6

Made up of 5 genes needed for development of anterior - head and thorax

Question 7

What is the role of BX-C?

Answer 7

Composed of 3 genes needed for development of posterior - abdominal and thorax

Question 8

What is the current model for how PS identity is regulated by HOM-C?

Answer 8

Based on Lewis’ genetic model using BX-C homeotic mutations and clarified by further molecular evidence, it states the most posterior acting gene determines PS identity and the earlier the gene in order on chromosome, the earlier it is expressed.