Understanding Human Genetics and Development

2. Chapter 3 Key Questions • What is our basic genetic endowment, and how can human development go off track? • How do the environment and genetics work together to determine human characteristics? • Which human characteristics are significantly influenced by heredity? • What happens during the prenatal stages of development?

3. Chapter 3 Key Questions • What are the threats to the fetal environment, and what can be done about them?

4. Earliest Development • This first cell is created when a male reproductive cell, a sperm, pushes through the membrane of the ovum, the female reproductive cell. • Gametes The sex cells from the mother and father that form a new cell at conception • Zygote The new cell formed by the process of fertilization

5. Genes and Chromosomes: The Code of Life • Genes The basic unit of genetic information • DNA (deoxyribonucleic acid) molecules The substance that genes are composed of that determines the nature of every cell in the body and how it will function • Chromosomes Rod-shaped portions of DNA that are organized in 23 pairs Refer to page 55 – Figure 3-1

6. Genes and Chromosomes: The Code of Life • Through a process called mitosis, which accounts for the replication of most types of cells, nearly all the cells of the body will contain the same 46 chromosomes as the zygote. • When the sperm and ova are formed in the adult human body in a process called meiosis, each gamete receives one of the two chromosomes that make up each of the 23 pairs.

7. Multiple Births: Two—or More—For the Genetic Price of One • Monozygotic twins Twins who are genetically identical (Come from the same zygote) • Dizygotic twins Twins who are produced when two separate ova are fertilized by two separate sperm at roughly the same time • Multiple births have increased with fertility drugs. More in White American • Mothers carrying multiple births experiences risk of premature births.

8. Boy or Girl? Establishingthe Sex of the Child • If the sperm contributes an X chromosome when it meets an ovum (which will always contribute an X chromosome), the child will have an XX pairing on the 23rd chromosome and will be a female. • If the sperm contributes a Y chromosome, the result will be an XY pairing and will be a male

9. The Basics of Genetics: The Mixing and Matching of Traits • We need to consider the basic mechanisms involved in the way that the genes we inherit from our parents transmit information. • Dominant trait The one trait that is expressed when two competing traits are present • Recessive trait A trait within an organism that is present, but is not expressed

10. The Basics of Genetics: The Mixing and Matching of Traits • Genotype The underlying combination of genetic material present (but not outwardly visible) in an organism • Phenotype An observable trait; the trait that actually is seen • Some of the genes form pairs called alleles, genes governing traits that may take alternate forms, such as hair or eye color.

11. The Basics of Genetics: The Mixing and Matching of Traits • Homozygous Inheriting from parents similar genes for a given trait (BB - Brown eyes, or bb - Blue Eyes) • Heterozygous Inheriting from parents different forms of a gene for a given trait (Bb – Brown Eyes)

12. Transmission ofGenetic Information • We can see this process at work in humans by considering the transmission of phenylketonuria (PKU), an inherited disorder in which a child is unable to make use of phenylalanine, an essential amino acid present in proteins found in milk and other foods. (Due to a recessive gene) • This is a reason for genetic couseling

13. Polygenic Traits • Polygenic inheritance (page 58) Inheritance in which a combination of multiple gene pairs is responsible for the production of a particular trait • Genes also vary in terms of their reaction range, the potential degree of variability in the actual expression of a trait due to environmental conditions. • X-linked genes Genes that are considered recessive and located only on the X chromosome

14. The Human Genome and Behavioral Genetics: Cracking the Genetic Code • Mapping the specific sequence of genes on each chromosome stands as one of the most important moments in the history of genetics, and, for that matter, all of biology. • Already, the mapping of the gene sequence has provided important advances in our understanding of genetics.

15. Behavioral Genetics • Behavioral genetics The study of the effects of heredity on behavior

16. Genetic Basis of Disorders and Traits

17. Inherited and Genetic Disorders: When Development Goes Awry • A recessive gene responsible for a disorder may be passed on unknowingly from one generation to the next, revealing itself only when, by chance, it is paired with another recessive gene. • In some cases, genes become physically damaged.

18. Inherited and Genetic Disorders: When Development Goes Awry • For instance, genes may break down due to wear-and-tear or to chance events occurring during the cell division processes of meiosis and mitosis. And sometimes, for no known reason, genes spontaneously change their form, a process called spontaneous mutation.

19. Inherited and Genetic Disorders: When Development Goes Awry Other inherited and genetic disorders include: • Down syndrome A disorder produced by the presence of an extra chromosome on the 21st pair; once referred to as mongolism • Fragile X syndrome A disorder produced by injury to a gene on the X chromosome, producing mild to moderate mental retardation

20. Inherited and Genetic Disorders: When Development Goes Awry • Sickle-cell anemia A blood disorder that gets its name from the shape of the red blood cells in those who have it • Tay-Sachs disease A disorder that produces blindness and muscle degeneration prior to death; there is no treatment • Klinefelter’s syndrome A disorder resulting from the presence of an extra X chromosome that produces underdeveloped genitals, extreme height, and enlarged breasts

21. Inherited and Genetic Disorders: When Development Goes Awry • Due to advances in behavioral genetics, genetic difficulties increasingly can be forecast, anticipated, and planned for before a child’s birth, enabling parents to take steps before the child is born to reduce the severity of certain genetic conditions.

22. Genetic Counseling: Predicting the Future From the Genes of the Present • Genetic counseling The discipline that focuses on helping people deal with issues relating to inherited disorders • Possible genetic defects, such as the presence of an extra sex chromosome, can be identified by assembling a karyotype, a chart containing enlarged photos of each of the chromosomes.

23. Prenatal Testing • Ultrasound sonography A process in which high-frequency sound waves scan the mother’s womb to produce an image of the unborn baby, whose size and shape can then be assessed • Chorionic villus sampling (CVS) A test used to find genetic defects that involves taking samples of hairlike material that surrounds the embryo

24. Prenatal Testing • Amniocentesis The process of identifying genetic defects by examining a small sample of fetal cells drawn by a needle inserted into the amniotic fluid surrounding the unborn fetus

25. Fetal DevelopmentMonitoring Techniques - page 63

26. Screening forFuture Problems • The newest role for genetic counselors involves testing people to identify whether they themselves, rather than their children, are susceptible to future disorders because of genetic abnormalities. • As our understanding of genetics continues to grow, researchers and medical practitioners have moved beyond testing and counseling to actively working to change flawed genes.

27. DNA-Based Genetic Tests page 64

28. DNA-Based Genetic Tests, cont’d

29. The Role of the Environment in Determining the Expression of Genes: From Genotypes to Phenotypes • As developmental research accumulates, it is becoming increasingly clear that to view behavior as due to either genetic or environmental factors is inappropriate. • A given behavior is not caused just by genetic factors; nor is it caused solely by environmental forces.

30. Temperament • Temperament Patterns of arousal and emotionality that represent consistent and enduring characteristics in an individual

31. Interaction of Factors • Such findings illustrate that many traits reflect multifactorial transmission, meaning that they are determined by a combination of both genetic and environmental factors. • In multifactorial transmission, a genotype provides a particular range within which a phenotype may achieve expression.

32. Studying Development: How MuchIs Nature? How Much Is Nurture? • Nonhuman Animal Studies: Controlling Both Genetics and Environment • It is relatively simple to develop breeds of animals that are genetically similar to one another in terms of specific traits. • By observing animals with similar genetic backgrounds in different environments, scientists can determine, with reasonable precision, the effects of specific kinds of environmental stimulation.

33. Contrasting Relatedness and Behavior: Adoption, Twin, and Family Studies • Nature conveniently has provided the potential to carry out various kinds of “natural experiments”—in the form of twins. • Because the inherited backgrounds of identical, monozygotic twins are precisely the same, any variations in their behavior must be due entirely to environmental factors.

34. Contrasting Relatedness and Behavior: Adoption, Twin, and Family Studies • Studies of nonidentical, dizygotic twins also present opportunities to learn about the relative contributions of nature and nurture. • The general conclusion resulting from decades of research: Virtually all traits, characteristics, and behaviors are the joint result of the combination and interaction of nature and nurture.

35. Physical Traits:Family Resemblances • Monozygotic twins are merely the most extreme example of the fact that the more genetically similar two people are, the more likely they are to share physical characteristics. • Other, less obvious physical characteristics also show strong genetic influences. For instance, blood pressure, respiration rates, and even the age at which life ends are more similar in closely related individuals than in those who are less genetically alike.

36. Intelligence: More Research, More Controversy • No other issue involving the relative influence of heredity and environment has generated more research than the topic of intelligence. • Genetics plays a significant role in intelligence.

37. Intelligence: More Research, More Controversy • Studies have shown that the closer the genetic link between two individuals, the greater the correspondence of their overall IQ scores. • Although it is clear that heredity plays an important role in intelligence, investigators are much more divided on the question of the degree to which it is inherited.

38. Genetic and Environmental Influences on Personality: Born to Be Outgoing? • Increasing research evidence suggests that some of our most basic personality traits have genetic roots. • Neuroticism, as used by personality researchers, is the degree of emotional stability an individual characteristically displays.

39. Genetic and Environmental Influences on Personality: Born to Be Outgoing? • Extroversion is the degree to which a person seeks to be with others, to behave in an outgoing manner, and generally to be sociable. • Clearly, genetic factors play a role in determining personality. At the same time, the environment in which a child is raised also affects personality development.

40. Mean Behavioral Scores

41. Psychological Disorders: The Role of Genetics and Environment • If genetics were the sole cause of psychological disorder, the risk for an identical twin would be 100%. • However, other factors account for disorders, ranging from structural abnormalities in the brain to a biochemical imbalance. • Several other psychological disorders have been shown to be related, at least in part, to genetic factors.

42. Psychological Disorders: The Role of Genetics and Environment • The role of genetics is often to produce tendency toward a future course of development. When and whether a certain behavioral characteristic will actually be displayed depends on the nature of the environment.

43. Can Genes Influence the Environment? • According to Scarr, the genetic endowment provided to children by their parents not only determines their genetic characteristics, but also actively influences their environment. • Children tend to actively focus on those aspects of their environment that are most connected with their genetically determined abilities.

44. Can Genes Influence the Environment? • Children also pay less attention to those aspects of the environment that are less compatible with their genetic endowment. • The genetically driven temperament of a child may evoke certain environmental influences.

45. Fertilization: The Momentof Conception • Fertilization The process by which a sperm and an ovum—the male and female gametes, respectively—join to form a single new cell • When sperm enter the vagina, they begin a winding journey that takes them through the cervix, the opening into the uterus, and into the fallopian tube, where fertilization may take place.

46. Fertilization: The Momentof Conception • Only a tiny fraction of the 300 million cells that are typically ejaculated during sexual intercourse ultimately survive the journey.

47. The Stages of the Prenatal Period: The Onset of Development The prenatal period consists of three phases: • germinal • embryonic • fetal

48. Stages of the Prenatal Period

49. The Germinal Stage: Fertilization to 2 Weeks • Germinal stage The first, and shortest, stage of the prenatal period, which takes place during the first 2 weeks following conception • Placenta A conduit between the mother and fetus, providing nourishment and oxygen via the umbilical cord

50. The Embryonic Stage: 2 Weeks to 8 Weeks • Embryonic stage The period from 2 to 8 weeks following fertilization during which significant growth occurs in the major organs and body systems • The outer layer of the embryo, the ectoderm, will form skin, hair, teeth, sense organs, and the brain and spinal cord.