- Sexual reproduction is seen across unicellular and multi-cellular organisms.
- In isogamous systems seen in unicellular organisms, instead of having male or female sexes, the organisms belong to either ‘plus’ or ‘minus’ categories which are similar to each other, but fusion can only take place in cells of opposite types.
- In the more complex organisms anisogamous system is seen where in there is sexual dimorphism and the organisms produce either of the distinct looking cells – a small motile sperm or a large stationary ovum (egg).
- The genetic basis for the transition from mating types to sexes has been a mystery.
- Until now, scientists believed that many genes, including the gamete-size determining gene, along with the sex determining genes allowed generation of distinct sex cells. But a recent experiment has proven that the MID gene alone was responsible for determination of sexes in algae.
- Scientists used the gene CrMID that determines the mating types from a unicellular algae namely Chlamydomonas reinhardtii , and a similar gene VcMID in the evolutionarily advanced Volvox carteri that produces distinct male and female reproductive cells (gametes).
- It was found that addition of VcMID gene to female V. carteri cells induced them to produce sperm and fertilise other females and removal of VcMID from male cells caused them to behave like and be fertilised by sperm like normal egg cells, though not as efficiently.
- They also established that VcMID works as the master sex-determining gene and attempts to substitute it with CrMID failed, proving that considerable changes have occurred in the gene over time.
- The study of reproductive evolution in algae will be useful in coming up with improved varieties of algae, which are now important as they are used in the production of biofuel.