Punnett squares can be used to depict crosses involving two factors, also called . In incomplete dominance, a heterozygote has a/n phenotype, mixing both of its parents’ phenotypes together. Human blood type is an example of , where both the A and B blood types can be expressed simultaneously. People with one copy of the allele that causes sickle cell anemia are called , while people with two copies of the allele have the disease. Respond to the following based on your reading. Using your knowledge of Punnett squares and hybridization, what is the probability that a purebred monohybrid, dihybrid, three-factor cross or higher will lead to the expression of dominant phenotypes in first-generation offspring? Why is it impossible to predict which of his or her two alleles each parent contributes for a given gene? As you've learned, thalidomide is a teratogen, meaning that it causes birth defects when taken by pregnant women. Another teratogenic compound is alcohol, which is known to cause birth defects in the developing child's nervous system and contribute to the development of fetal alcohol syndrome. Can you explain the function of teratogens such as thalidomide and alcohol in terms of environmental factors that play a role in organismal development? What does the presence of teratogens mean for pregnant women who wish to have a healthy pregnancy for both themselves and their future children? Some animals that look like they exhibit codominance actually do not. For example, the zebra, famous for its black and white stripes, obtains its pattern from a series of genes that initiate the production of a dark pigment called melanin on specific parts of its body. Different zebras can have different patterns of stripes as dictated by their genetic code. For example, the plains zebra has wide stripes, while the Grevy's zebra has narrow stripes. What are some other examples of striped and spotted animals that are genetically encoded to have these designs? The fact that the zebra's stripes are p