3C Cell Differentiation

the process by which a less specialised cell becomes more specialised for a particular function

• by comparing the proteins contained in cells - this enables us to work out which genes have been expressed and which have been supressed

place on a chromosome where any particular gene is found

• some features are determined by multiple alleles, meaning that there are more than two possible variants • no matter how many possible alleles there are, any one diploid individual will only inherit two of them • example= human ABO blood group system, A and B are dominant to O, so the O blood group is recessive, but A and B are codominant

both alleles are expressed in phenotype and produce a protein

• characteristic is coded by more than one gene on different loci • example= eye colour, weight • further variety is added by interaction with environment

• small sample size • experimental error • process is random so the unexpected can happen • could mean that the genes being examined are both on the same chromosome (linked)

9:3:3:1

when genes for two different characteristics are found on the same chromosome and are close together so they are linked and inherited as a single unit

• when genes are closely linked (located close to each other on the chromosome) then recombination events which separate them rarely occur during meiosis • if the genes are located further appart on chromosome, then the number of recombination events in meiosis may be higher • so the tightness of the linkage of a pair of genes is related to how close together the linked genes are located on the chromosome • genes that are very close together are less likely to be split during the crossing over stage of meiosis than genes that are further appart • if genes are further appart, crossing over is more likely to occur