Biology 11 – Unifying Concepts of Biology
“Activity 4.1 – BISDAK Headline: Zygote from two sperm
cells?”
After reading an excerpt of the news, answer the following question:
Which of the following predictions do you think they would make? Justify your choice,
and explain why you rejected each of the other choices.
Answer: b. the zygote could be genetically identical to the gamete donor, but it is much
more likely that it would have an unpredictable mixture of chromosomes from the
gamete donor's parents.
Consider what would have to happen to produce a zygote genetically identical to
the gamete donor: the zygote would have to have a complete set of the donor's material
chromosomes and a complete set of the donor's parental chromosomes. The first gamete
in this union could contain any mixture of maternal and parental chromosomes, but once
that first gamete was "chosen," the second one would have to have one particular
combination of chromosomes- the combination that supplies whatever the first gamete
did not supply. So, for example, if the first three chromosomes of the first gamete were
maternal, maternal, and parental, the first three of the second gamete would have to be
paternal, paternal, and maternal. The chance that all 23 chromosome pairs would be
complementary in this way is only one in 2^23 (or one is 8,388,608). Because of
independent assortment, it is much more likely that the zygote would have an
unpredictable combination of chromosomes from the donor's father and mother.
Rejected Choices:
a.) The zygote would have 46 chromosomes, all of which came from the gamete
donor (its one parent), so the zygote would be genetically identical to the gamete
donor.
= Indeed the zygote would have 46 chromosomes from the 23 chromosomes each
from the gametes. However, this does not mean that the zygote would genetically
identical to the gamete donor since it would not only have to have a complete set
of the donor's material chromosomes, but also a complete set of the donor's
parental chromosomes.
“Activity 4.1 – BISDAK Headline: Zygote from two sperm
cells?”
After reading an excerpt of the news, answer the following question:
Which of the following predictions do you think they would make? Justify your choice,
and explain why you rejected each of the other choices.
Answer: b. the zygote could be genetically identical to the gamete donor, but it is much
more likely that it would have an unpredictable mixture of chromosomes from the
gamete donor's parents.
Consider what would have to happen to produce a zygote genetically identical to
the gamete donor: the zygote would have to have a complete set of the donor's material
chromosomes and a complete set of the donor's parental chromosomes. The first gamete
in this union could contain any mixture of maternal and parental chromosomes, but once
that first gamete was "chosen," the second one would have to have one particular
combination of chromosomes- the combination that supplies whatever the first gamete
did not supply. So, for example, if the first three chromosomes of the first gamete were
maternal, maternal, and parental, the first three of the second gamete would have to be
paternal, paternal, and maternal. The chance that all 23 chromosome pairs would be
complementary in this way is only one in 2^23 (or one is 8,388,608). Because of
independent assortment, it is much more likely that the zygote would have an
unpredictable combination of chromosomes from the donor's father and mother.
Rejected Choices:
a.) The zygote would have 46 chromosomes, all of which came from the gamete
donor (its one parent), so the zygote would be genetically identical to the gamete
donor.
= Indeed the zygote would have 46 chromosomes from the 23 chromosomes each
from the gametes. However, this does not mean that the zygote would genetically
identical to the gamete donor since it would not only have to have a complete set
of the donor's material chromosomes, but also a complete set of the donor's
parental chromosomes.
