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Chapter 12
What confounding problems could have been seen if Mendel had chosen another plant
with exposed male and female structures? (Figure 12.3)
Answer: The ability to control whether the plants self-fertilized or cross-fertilized was of
paramount importance in Mendel’s studies. Results due to cross-fertilization would have
had confounding influences on the predicted number of offspring with a particular
phenotype.
If one of the affected females in the third generation married an unaffected male, could
she produce unaffected offspring? If so, what are the chances of having unaffected
offspring? (Figure 12.8)
Answer: Each of the affected females in the study had one unaffected parent, which
means that each is heterozygous for the dominant trait. If each female marries an
unaffected (recessive) male, each could produce unaffected offspring. The chance of
having unaffected offspring is 50% in each case.
From a genetic disease standpoint, why is it never advisable for close relatives to mate
and have children? (Figure 12.9)
Answer: Genetic defects that remain hidden or dormant as heterzygotes in the recessive
state are more likely to be revealed in homozygous state among closely related
individuals.
Many studies of identical twins separated at birth have revealed phenotypic differences in
their development (height, weight, etc.). If these are identical twins, can you propose an
explanation for these differences? (Page 233)
Answer: Almost certainly, differences in major phenotypic traits of twins would be due
to environmental factors such as diet.