Video Transcript
Complete the following
sentence. Asexual reproduction produces
offspring that are blank identical to the parents, so it reduces genetic blank. (A) Not, expression; (B)
genetically, variation; (C) almost, mutations; or (D) partially, similarities.
The two words in each answer choice
will be used to fill in each of the two blanks. For example, if we choose the
answer choice almost, mutations, then we would be saying that the correct sentence
should read “Asexual reproduction produces offspring that are almost identical to
the parents, so it reduces genetic mutations.” To fill in the first blank of the
sentence, we need to know the relationship between offspring produced by asexual
reproduction and their parents.
You may recall that asexual
reproduction requires only one parent. So let’s take a look at a single
bacterium as it undergoes the common form of asexual reproduction called binary
fission. Bacteria are prokaryotes, so their
DNA floats freely in the cytoplasm, often in the form of a circular chromosome. As the bacterium enlarges to
prepare for division, it makes a copy of its chromosome. The bacterium then splits into two
daughter bacteria, each containing a copy of the chromosome. Because there is no second parent
to mix genes with, the two daughter bacteria are genetically identical. Or to put it another way, they are
clones of each other. So we have determined that the
correct term to fill in the first blank is genetically.
Unlike asexual reproduction, sexual
reproduction requires two parents, with the biological father typically providing
the sperm cell and the biological mother providing an egg cell. After the sperm and egg unite in a
process called fertilization, they form a structure called a zygote. And the nucleus of the zygote will
have genetic material from both of the biological parents, represented here by green
and pink squiggly lines. The zygote will divide and grow,
eventually becoming a fully functioning offspring.
Because of how genes are rearranged
and inherited during sexual reproduction, this new offspring will be genetically
unique from its biological parents and from any additional offspring those same
parents have together. Each instance of sexual
reproduction produces genetically unique offspring. And over time, this increases the
genetic variation within a population, which refers to the differences in the
genetic material between individuals in the same population.
In contrast, if we look at asexual
reproduction over time, we can see that the same chromosome is copied and passed
down to each generation of offspring, leading to a population of clones with reduced
genetic variation. This example shows that the correct
term to fill in the second blank is variation. So the correct complete sentence is
“Asexual reproduction produces offspring that are genetically identical to the
parents, so it reduces genetic variation.”
