1													2
																		3		4
							5				6				7																		8									9
									10					11								12																		13
	14
				15		16		17
													18
																								19
																											20		21									22
23
													24
								25																		26
																															27									28
					29
		30								31																							32
	33																																										34
								35
										36																						37
					38
																					39
	40														41
																							42
						43												44		45
					46			47																			48
	49
																				50
51
																							52
																				53											54
			55																								56
	57																58										59

Across 1. the result of two separate eggs fertilized by two sperm, also called fraternal twins 5. substance that protects the fetus's skin during development 7. variations of genes 12. newborns who weigh less than 3 pounds 17. disorder affecting babies whose mothers consumed large amounts of alcohol while they were pregnant 18. group of nucleotide bases that provides a specific set of biochemical instructions 20. allele whose instructions are ignored in the presence of a dominant allele 23. prenatal diagnostic technique that uses a syringe to withdraw a sample of amniotic fluid through the mother's abdomen 24. newborns who weigh less than 2 pounds 25. effort to improve the human species by letting only people whose characteristics are valued by a society mate and pass along their genes 27. apperance of the top of the baby's head during labor 29. process by which sperm and an egg are mixed in a petri dish to create a zygote, which is then placed in a woman's uterus 32. inner sac in which the developing child rests 33. molecule composed of four nucleotide bases that is the biochemical basis of heredity 35. principle of physical growth that states that structure nearest the center of the body develop first 36. physical, behavioral, and psychological features that result from the interaction between one's genes and the environment 38. surgical removal of infant from the uterus through an incision made in the mother's abdomen 39. a birth complication in which umbilical blood flow is disrupted and the infant does not receive adequate oxygen 40. newborns who weigh less than 5 pounds 42. person's hereditary makeup 43. threadlike structures in the nuclei of cells that contain genetic material 45. a measure of the extent to which a trait or characteristic is inherited 47. the result of a single fertilized egg splitting to form two new individuals; also called identical twins 48. fertilized egg 50. longest period of prenatal development, extending from the 9th until the 38th week after conception 51. structure containing veins and arteries that connects the developing child to the placenta 53. term given to the zygote once it is completely embedded in the uterine wall 54. disorder in which the embryo's neural tube does not close properly 55. outer layer of the embryo, which will become the hair, the outer layer of skin, and the nervous system 56. middle layer of the embryo, which becomes the muscles, bones, and circulatory system 57. prenatal diagnostic technique that uses sound waves to generate an image of the fetus 58. inner layer of the embryo, which becomes the lungs and the digestive system 59. the number of infants out of 1,000 births who die before their first birthday

Down 2. forces within a family that make siblings different from one another 3. 23rd pair of chromosomes; these determine the sex of the child 4. a principle of physical growth that states that structures nearest the head develop first 6. step in which the zygote burrows into the uterine wall and establishes connections with a woman's blood vessels 8. physical and psychological responses to threatening or challenging conditions 9. field of medicine concerned with treating prenatal problems before birth 10. inherited disorder in which the infant lacks a liver enzyme 11. structure through which nutrients and wastes are exchanged between the mother and the developing child 13. small cluster of cells near the center of the zygote that will eventually develop into a baby 14. first 22 pairs of chromosomes 15. an agent that causes abnormal prenatal development 16. when phenotypes are the result of the combined activity of many separate genes 19. age at which a fetus can survive because most of its bodily systems function adequately; typically at 7 months after conception 21. prenatal diagnostic technique that involves taking a sample of tissue from the chorion 22. progressive and fatal type of dementia caused by dominant alleles 26. fluid that surrounds the fetus 28. the branch of genetics that studies the inheritance of behavioral and psychological traits 30. wrinkled surface of the brain that regulates many functions that are distinctly human 31. situation in which one allele does not dominate another completely 34. disorder in which individuals show signs of mild anemia when they are deprived of oxygen; occurs in individuals who have one dominant allele for normal blood cells and one recessive sickle-cell allele 37. the many changes that turn a fertilized egg into a newborn human 41. when the alleles in a pair of chromosomes differ from each other 44. process of deliberately seeking environments that are compatible with one's genetic makeup 46. form of an allele whose chemical instructions are followed 49. when the alleles in a pair of chromosomes are the same 52. babies born before the 36th week after conception