Cells go through a repeating cycle of events in growth regions such as plant root tips and animal embryos. Outline this cell cycle.

Draw a labelled diagram of the formation of a chiasma by crossing over.

Explain the control of gene expression in eukaryotes.

a. mitosis is the division of a nucleus to produce two genetically identical daughter nuclei 

b. consists of four phases: prophase, metaphase, anaphase, telophase 

c. cytokinesis occurs after mitosis 

d. interphase is the metabolically active phase between cell divisions  OWTTE

e. the interphase consists of the S phase, G1 and G2 

f. DNA replicates in the S phase 

g. cell growth
OR
preparation for mitosis
OR
duplication of organelles in G1 and G2

a. «crossing over/chiasmata shown between» homologous chromosomes  

b. centromere drawn and labelled  

c. single strand break «SSB»/DNA cut between homologous chromosomes 

d. non-sister chromatids labelled
OR
sister chromatids labelled 

e. chiasma between homologous chromosomes labelled «shown forming after SSB»

Homologous chromosomes must be labelled and correctly drawn.

It is likely that more than one diagram will need to be included to demonstrate the stages.

a. mRNA conveys genetic information from DNA to the ribosomes «where it guides polypeptide production» 

b. gene expression requires the production of specific mRNA «through transcription» 

c. most genes are turned off/not being transcribed at any one time/regulated
OR
some genes are only expressed at certain times 

d. some genes are only expressed in certain cells/tissues
OR
«cell» differentiation involves changes in gene expression 

e. transcription factors/proteins can increase/decrease transcription 

f. hormones/chemical environment of cell can affect gene expression 

g. example of cell environment
eg: auxin/insulin/cytoplasmic gradient in embryo

h. transcription factors/proteins may prevent or enhance the binding of RNA polymerase 

i. nucleosomes limit access of transcription factors to DNA/regulate gene expression/transcription
OR
activate or silence genes 

j. DNA methylation/acetylation appears to control gene expression «as epigenetic factor»
OR
methylated genes are silenced 

k. «some» DNA methylation patterns are inherited 

l. introns may contain positive or negative gene regulators
OR
gene expression can be regulated by post-transcriptional modification/splicing/mRNA processing