6.1.6 Gene Control: Body Plans

Question 1

Facts

Answer 1

Genes which are functioning or not functioning at particular times need to be switched on and off. Done by transcription factors

Question 1

Homeobox Genes

Answer 1

• DNA sequence coding for transcription factors
• Transcription factors attach to DNA at specific locations and regulate transcription of genes
• Homeobox gene contains homeobox sequence
• In animals, plants and fungi they are highly conserved so remain unchanged from an evolutionary standpoint (universal)
• If mutations in these homeobox sequences occur, then organisms may not be favourable for natural selection, which is why the sequences are so highly conserved, because only the organism with the best coded genetics can survive
• Homeobox genes are responsible for genetic control in organisms
• Help to form pattern of body
• Eg. Polarity of organism, developing into head and tail
• Control segmentation of organisms like forming distinct body parts like abdomens and limbs
• ‘Master genes’

Question 2

Hox genes

Answer 2

• Subsection of homeobox genes
• Determine identity of embryonic body regions
• Hox genes are organised into hox clusters
• Vertebrates have 4, found on different chromosomes
• Linear order, affecting regions of body they affect