Video Transcript
Which of the following statements
about chromosomes is true? (A) Chromosomes are linear
molecules within the cytoplasm of cells that contain protein chains. (B) In general, every somatic cell
of a particular living organism contains the same number of chromosomes. (C) In every new generation of a
species, the number of chromosomes doubles. Or (D) each human somatic cell
contains 46 pairs of chromosomes.
To answer this question, let’s
first define what chromosome means. Chromosomes are highly compacted,
long strands of DNA that contain instructions for the functions of life and
reproduction. Typically, the majority of an
organism’s genetic material is stored within a chromosome.
In eukaryotic cells, like plant or
animal cells, chromosomes are contained in the nucleus of the cell. So we can eliminate (A), as the
cytoplasm is the area in a cell outside of the nucleus.
In humans, the cell nucleus
contains 46 total chromosomes, or 23 pairs of chromosomes. So we can eliminate (D), as it
indicates human cells contain 46 pairs of chromosomes, which would be 92 chromosomes
in total. This is not correct.
These 46 total chromosomes in human
cells come from the joining of the parents’ gametes, or sex cells. Typically, each sperm and egg will
contain 23 chromosomes, or half of what other body cells contain. When the contents of the parents’
gametes are joined together, it results in an offspring with 46 total chromosomes in
its cells. When this offspring produces its
own gametes, those gametes will also contain half of the total chromosomes, that is,
23 chromosomes.
Since the total chromosomes in an
individual will be halved every time that gametes are produced, every new generation
of offspring will receive the same number of chromosomes from their parents. That is, each offspring will
receive 23 chromosomes from each parent, resulting in 46 chromosomes total for that
individual. So we can eliminate (C), since each
generation receives the same number of chromosomes, not double.
The gametes we just mentioned are
referred to as sex cells, whereas other cells in the body are referred to as somatic
cells. A major difference between these
types of cells is the number of chromosomes they contain. Somatic cells will contain an
individual’s entire genetic information, whereas sex cells will contain only half of
it.
Additionally, although somatic
cells may differentiate into different types of specialized cells, such as heart
cells, or lung cells, or liver cells, they all contain the same DNA. That is, they all contain the same
full number of chromosomes, which in humans is 46. They may express the genes within
the chromosomal DNA differently, but all the chromosomes are there in any type of
somatic cell.
Therefore, the correct answer to
this question is (B). The true statement is that, in
general, every somatic cell of a particular living organism contains the same number
of chromosomes.
