D2.2  Gene Expression

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How is gene expression changed in a cell?
• How can patterns of gene expression be conserved through inheritance?

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What mechanisms are there for inhibition in biological systems? 
• In what ways does the environment stimulate diversification? 

AHL ​​​​​​​D2.2.1— Gene expression as the mechanism by which information in genes has effects on the phenotype.

• Define genotype and phenotype.
• Define gene expression.  
• List the most common stages in the process of gene expression.​

AHL ​​​​​​​D2.2.2— Regulation of transcription by proteins that bind to specific base sequences in DNA. 

• Explain the regulation of transcription by a transcription factor binding to the promoter sequence of DNA.
• Compare the function of enhancer and silencer DNA sequences. 
• Compare the function of repressor and activator transcription factors.

AHL ​​​​​​​D2.2.3-- Control of the degradation of mRNA as a means of regulating translation.

• Outline how the length of the poly-A tail on mRNA impacts degradation of mRNA by nucleases.
• Outline how the degradation of mRNA is a mechanism of regulating translation.

AHL ​​​​​​​D2.2.4- Epigenesis as the development of patterns of differentiation in the cells of a multicellular organism.  

• Define epigenesis and epigenome.​

AHL ​​​​​​​D2.2.5— Differences between the genome, transcriptome and proteome of individual cells.

• Compare the genome, transcriptome and proteome.​

AHL ​​​​​​​D2.2.6- Methylation of the promoter and histones in nucleosomes as examples of epigenetic tags.

• Describe the impact of methylation of DNA in the promoter of DNA on gene expression.
• Describe the impact of acetylation and methylation of histone proteins on gene expression.

 AHL ​​​​​​​​​​​D2.2.7- Epigenetic inheritance through heritable changes to gene expression.

• Describe the inheritance of epigenetic tags in differentiated cells of a multicellular organism.
• Discuss the consequences of reprogramming and imprinting of epigenetic tags in haploid gametes.

AHL ​​​​​​​D2.2.8- Examples of environmental effects on gene expression in cells and organisms.

• Outline the impact of air pollution on the epigenetic regulation of genes associated with the immune response. 

AHL ​​​​​​​D2.2.9- Consequences of removal of most but not all epigenetic tags from the ovum and sperm.

• Discuss how imprinting of epigenetic tags impacts gene expression in a diploid cell.
• Outline the epigenetic origins in the difference in size between tigons and ligers (lion–tiger hybrids).

AHL ​​​​​​​D2.2.10- Monozygotic twin studies.

• Explain the reason why monozygotic twin studies are often used to measure the impact of the environment on gene expression.​

AHL ​​​​​​​D2.2.11- External factors impacting the pattern of gene expression.

• Outline the mechanism by which the presence of lactose regulates the expression of genes related to digestion and use of lactose in E. coli. 
• Outline the mechanism by which the presence of oestrogen in a cell’s environment regulates the expression of genes related to endometrium development and maintenance during the uterine cycle.  ​