Video Transcript
Which of the following Punnett
squares correctly shows the inheritance of sex chromosomes in humans?
A Punnett square is a useful tool
to show the inheritance of genetic material in the offspring from their parents. When organisms reproduce, their
gametes or sex cells combine during fertilization. Each gamete contains 23 chromosomes
to give a total of 46 chromosomes in the embryo. The first 22 pairs of chromosomes
are called autosomes, and the 23rd pair are called the sex chromosomes.
In humans, there are two types of
sex chromosomes, called X and Y. Biological females have two copies
of the X chromosome, and biological males have a single copy of the X chromosome and
a single copy of the Y chromosome. So when gametes are produced, the
ovum will always contain an X chromosome, while the sperm will contain an X or a Y
chromosome.
Now let’s fill in a Punnett square
to determine the inheritance of sex chromosomes in humans. On the top will be the female
gametes, which will be either X or X. And on the side will be the male’s
gametes, which will be either X or Y. Now we simply combine them, so the
first combination will be a female with one X chromosome from each parent. And if we complete the rest of the
Punnett square, we’ll see that the correct answer is answer choice (D).
