Video Transcript
Which of the following is a
defining feature of a gamete? (A) A gamete contains double the
genetic material of a normal body cell. (B) A gamete contains half the
genetic material of a normal body cell. (C) A gamete is able to replicate
and divide indefinitely. Or (D) a gamete is formed by
mitosis, not meiosis.
This question asks us about
gametes, otherwise known as sex cells, which are very important for the process of
sexual reproduction. Can you remember how sex cells are
formed? They are produced through a process
called meiosis. Most cells in the human body are
called somatic cells, and they make up every organ and tissue apart from the sex
cells contained in the gonads. Human somatic cells tend to contain
46 chromosomes. They are called diploid cells
because they have a full set of genetic material having received DNA from both a
biological mother and biological father.
These two sets of DNA are provided
by the gametes, which are haploid cells as they contain half the number of
chromosomes of typical somatic cells, which in humans is only 23 chromosomes as
opposed to 46. Gametes are called egg cells in
biological females and sperm cells in biological males. Unlike gametes, which are formed
through meiosis, somatic cells are produced by mitosis, which allows normal body
tissues to grow by increasing their cell number. As this question focuses on the
defining features of gametes, let’s take a closer look at meiosis.
The process of meiosis converts a
diploid cell into four haploid cells by halving the genetic information in the
original cell. Let’s take a look at an example of
a diploid cell with six chromosomes, three that came from the biological mother and
three that came from the biological father, arranged into homologous pairs. Before meiosis can begin, these six
chromosomes are replicated. During the first phase of meiosis,
the homologous pairs of chromosomes are pulled apart into separate cells, halving
the number of chromosomes in each cell compared to the original diploid cell.
The cells will then undergo a
second division during meiosis, which pulls apart each replicated chromosome to
produce four haploid gametes, which in this example will each contain only three
chromosomes. In other words, each gamete
contains half the genetic material of the original diploid body cell. We now have enough information to
answer our question. The defining feature of a gamete is
(B). A gamete contains half the genetic
material of a normal body cell.