What are sexual and asexual reproduction and how do they work?
Sexual reproduction: The process of forming a new organism from the fusion of the offspring’s
parents’ (male + female) gametes. Gametes are sex cells such as sperm and egg cells for humans.
The offspring that is formed from sexual reproduction has the genetic material that is derived from
its parents. However, in almost* all cases the offspring’s genetic material is NOT IDENTICAL to their
parents (it’s mixed). In humans and many other mammals such as cows this process of producing
gametes is called meiosis.
*Note that self pollination involves one plant (parent) and is a type of sexual reproduction. This is
because the plant can produce both pollen and ovules (male and female plant gametes). These
gametes can combine to produce either a genetically identical offspring or genetically different
offspring. Whether the offspring is genetically identical or different, it will depend of whether the
single parent plant is homozygous or heterozygous for those genes. We will learn about these two
terms when you learn about Punnett Square in Week 4’s notes.
Asexual reproduction: Asexual reproduction is the process of forming an offspring (usually a cell)
from just ONE parent through cell division. Depending on the cell division process, there may be
many names. For example, in humans and many other mammals, this cell division process is called
mitosis. Thus, the offspring has genetic materials that is IDENTICAL to that of its single parent –
offspring is a CLONE of the parent.
The most important distinguishing factor between sexual and asexual reproduction is whether or not
the fusion of gametes occurred. For sexual reproduction, there must be a fusion of gametes
whereas, in asexual reproduction, there is no fusion of gametes.
How sexual and asexual reproduction processes allow parents’ genetic information to be passed on
to their offspring, and thus, ensuring the continuity of the species?
During reproduction, the parents’ genetic information (DNA) is copied and passed onto the
offspring. The offspring’s genetic material is stored in their cells’ nucleus.
There are two types of cells: somatic and non-somatic (sex) cells. Since humans and many other
mammals cannot produce offspring via asexual means, all offsprings produced are from non-somatic
cells. Hence, only the parents’ genetic material in non-somatic cells’ (or sex cells’) genetic material is
passed onto the offspring.
Genetic information is passed onto the next generation (offspring). Thus, ensuring the continuity of
the species.
By week 3’s notes, you will see the importance of creating variation in offspring’s genetic
information (new allele combinations, increasing variation in the alleles which gametes can inherit as
well as variation in the gametes that are fertilised during fertilisation). Don’t worry if you don’t know
what genes and alleles are, we will look into their definitions and role in genetics in Week 2.
Essentially, the point is that you will see how the increased variation in the offspring’s genotype will
enhance the chances of survival of a species’ population and thus supporting the continuity of the
species. In Week 4’s notes, you will see how mutation (apart from sexual and asexual reproduction)
can also create genetic variation.
A third point is that reproduction would increase the total number of offsprings in a population,
effectively increasing population size. Thus, supporting the continuity of species.
What is evolution?
Evolution is the change in living organism’s genetic information, favourable characteristics and
phenotypes (appearance or physical traits) over many generations.
For now, just know that genetic information contributes to an organism’s phenotype. In terms of
how this works, this will be comprehensively covered in the upcoming weeks.
But what drives evolution aka. the change in genetic information, for example, how a rainbow
unicorn population can slowly turn into a pack of green unicorns, over time?