Answer to Question 1
The procedure for IVF is to take a donor egg and donor sperm and mix them
together in a Petri dish in the lab. Once a viable embryo is produced, it is implanted
in the mother's uterus. The donors can be a married or committed couple or outside donors. Some of the benefits are: sperm sorting can be accomplished at the same
time to increase the likelihood of a desired sex in the fetus. Since a couple can use
their own sperm and eggs (unless physical abnormalities prevent this), the child is
biologically theirs. Some of the risks are those associated with any multiple birth
since typically more than one embryo is implanted. These risks include higher rates
of birth defects, small birthweight, and premature birth. This is especially an issue in
the United States since there are no laws regulating the number of embryos that can
be implanted.
Answer to Question 2
Monozygotic twins result from one ovum being penetrated by one sperm. At an early
point in cell division, the cluster of cells splits into two identical halves. The
genotypes are identical from conception through birth, but the phenotypes can be
altered through variations in genetic replication and environmental influences
throughout the life span. In other words identical twins may not look identical their
entire lives. Also, the genotype itself may be altered over the life span.
Dizygotic twins, also called fraternal twins, result from two separate ova being
fertilized by two separate sperm. Their genotypes, and therefore their phenotypes,
are not any more likely to be identical than regular siblings.
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An example of external fertilization.
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