| stem cell | an undifferentiated cell that has the ability to specialise into any type of cell |
| pluripotent | a type of stem cell that are able to differentiate into any type of cell except placental cells |
| totipotent | type stem cells that are able to differentiate into any type of cell including placental cells |
| how are stem cells used in medical therapies? | treat diseases
replace damaged tissues |
| name two sources of stem cells | embryonic stem cells from embryos
adult stem cells from the bone marrow |
| stem cell therapy disadvantages | embryos are destroyed in the process
risk of infection - may become cancerous |
| how do cells differentiate? | a stimulus acts on an unspecialised cell
activator and repressor molecules bind to the promoter region on the DNA
some genes are active whilst others not
the active genes are transcribed and mRNA is produced
the mRNA is translated in the ribosome producing a protein
the protein is able to change the structure and function of a cell |
| how are multicellular organisms organised? | cell make up tissues
tissues make up organs
organs make up the organ system |
| phenotype | the characteristics of an organism that result from the interaction of the organisms genes and its environment |
| genotype | an organisms genetic composition |
| what are epigenetic changes? | they modify the activation of certain genes
they do not change the base sequence in DNA |
| two examples of epigenetic changes | DNA methylation
histone modification |
| DNA methylation | process where methyl groups are added to DNA
modifies the function of DNA by supressing gene transcription
the change is permanent preventing the cell turning back into a stem cell or any different cell type |
| Histone modification | acetylation
methylation |
| what is polygenic inheritance? | where multiple alleles for the same gene at different loci determine the phenotype of an organism |
| examples of polygenic traits | height
eye colour
hair colour |
| why does polygenic inheritance give rise to continuous variation? | the polygenic traits are different types of variation that are able to be distributed on a continuum |
