Answer to Question 1
A
Answer to Question 2
Simple dominance applies to a variety of physical traits such as eye color, hair color, and disorders such as PKU and Tay-Sachs disease. These traits are determined by a single pair of genes, called alleles; the dominant allele is the one that is actually expressed. A recessive trait can only be expressed if both alleles are recessive. Thus, if D stands for dark hair and d stands for blond hair, the phenotype will be dark hair with the combinations DD, Dd, and dD. The phenotype will be blond hair only with dd. Codominance occurs when the phenotype is a compromise between two alleles, as with blood type AB, which occurs when a type A allele and a type B allele combine and are equally expressed in the phenotype. Genetic imprinting occurs when a gene pair contains a biochemical marker that allows one parent's allele (either the mother's or the father's) to be expressed, regardless of its composition. This means that some traits are more likely to appear in offspring when the father displays that trait, and that other traits are more likely to be displayed in offspring when the mother displays the trait. An example of a trait that shows paternal genetic imprinting is diabetes; a trait that shows maternal genetic imprinting is Angelman syndrome.
Enzymatic features of DNA polymerase that account for its inability to copy one of the DNA strands a
Testing Infant’s Understanding of Quantity
An infant lying in the crib, looking at the mobiles hanging above him.
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Daily Calorie Intake from Sugar Drinks, United States, 2005–2008
Igneous Features