Distinguish between genotype and phenotype and explain how the environment may affect each. What ...

1) Genotype is the actual DNA sequence or genetic makeup of an individual. Teratogens (agents that cause mutations) might damage the DNA and change the genotype. For instance, the DNA in an embryo exposed to ionizing radiation might be damaged, resulting in genes that malfunction. Phenotype is the physical expression of the genes. Height, hair color, and even enzyme activity are phenotypes. If the genotype is changed by the environment, the phenotype may also be changed. A single base change in DNA is responsible for the sickle cell phenotype. Phenotype is dependent on the environment in a variety of ways. One example is that a child might have the genotype tall. If the child doesn't receive adequate nutrition, though, he still might not be as tall as his genes would ordinarily allow.

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2) d

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3) e

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4) b

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5) e

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6) c

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7) The position of the fetus and placenta is identified via ultrasound and palpation, and the skin is prepared with antiseptic and local anesthetic. A hypodermic needle is inserted through the abdominal wall and uterus to withdraw 10 mL of amniotic fluid from the amniotic cavity. The fluid and cells are examined and biochemically tested for abnormal proteins and chromosome abnormalities that may signal fetal problems and congenital defects.

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8) e

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9) d

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10) The primary germ layers are the endoderm, mesoderm and ectoderm. The endoderm ultimately develops into tissues such as epithelial linings and associated glands in the respiratory, digestive and reproductive systems. The mesoderm becomes connective tissues, muscle tissues and the dermis. The ectoderm yields the epidermis, the nervous system and some additional epithelial membranes.

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