6.1.6 Gene Control: Body Plans

Question 1

What is a homeobox? And so what is a homeobox gene?

Answer 1

DNA sequence coding for transcription factor protein

A gene containing a homeobox sequence

Question 2

Why are homeobox sequences so similar in plants, animals and fungi?

Answer 2

• Maintained by natural selection and evolution
• Mutations causing change in these homeobox sequences can lead to organisms being unfavourable by natural selection (strong negative selection pressure keeps sequences highly conserved)
• They all code for the same amino acids because DNA binding regions must all be the same shape

Question 3

What are homeobox genes responsible for?

Answer 3

• Genetic control of development of body plans in different organisms
• So form basic pattern of body
• Eg. By controlling polarity of organism (which end forms the head, the tail, etc)
• Eg 2. Controls segmentation of organisms like insects, or in mammals limbs, and what organs are present where
• ‘Master’ genes controlling which other genes function and when at different stages of development

Question 4

What are hox genes?

Answer 4

• Subset of homeobox genes
• Determine identity of embryonic body regions along head-tail axis
• Organised into hox clusters
• Vertebrates have 4 (each containing 9-11 hox genes), found on different chromosomes
• Linear order to hox genes in their clusters, directly related to the order of the regions of the body they affect