Beginnings PART 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Guideposts for Study 1. How does conception normally occur, and how have beliefs about conception changed? 2.What causes multiple births? 4. What genetic mechanisms determine sex, physical appearance, and other characteristics?

Conception ___________ – to make a genetic copy of an individual A single sperm, one of millions from the biological father, joins an ovum, one of several hundred thousand produced by the biological mother's body  ____________

Uniqueness Which sperm meets which ovum will have tremendous implications for the new person Changing ideas: Did a stork bring you? Are you a boy because you were conceived under a new moon?

Becoming Parents What Causes Multiple Births? ________________twins: Twins conceived by the union of two different ova (or a single ova that has split) with two different sperm cells; also called fraternal twins. ________________ twins: Twins resulting from the division of a single zygote after fertilization; also called identical twins. The rise in multiple births is due to a trend toward delayed childbearing and increased use of fertility drugs _______________________ Inability to conceive a baby after 12 months of trying

Mechanisms Of Heredity The Genetic Code Basis of heredity is a chemical called deoxyribonucleic acid ( ), which contains all the inherited material passed from biological parents to children Every cell except the sex cells has _____ pairs of chromosomes – _______in all Genetic action that triggers growth of body and brain is often regulated by hormones

The Genetic Code continued… Chromosomes: Coils of DNA that carry genes. _________: Small segments of DNA located in definite positions on particular chromosomes. Human genome: Complete sequence or mapping of genes in the human body and their locations. _________: Complex process of cell division in which each gamete (sperm or ovum) ends up with only 23 chromosomes-one from each pair. _________: Process by which cells divide in half over and over again duplicating themselves.

Mechanisms Of Heredity What Determines Sex? Sex chromosomes are either ___ chromosomes or _____chromosomes When an ovum (___) is fertilized by an X- carrying sperm, the zygote formed is ______, a female When an ovum (X) is fertilized by a _____- carrying sperm, the resulting zygote is ______, a male

_____: Paired genes that affect a trait. Homozygous: two identical alleles for a trait. Heterozygous: two different alleles for a trait. ________________ inheritance: Pattern of inheritance in which, when a child recieves contradictory alleles, only the dominant one is expressed. _________________ inheritance: Pattern of inheritance in which a child recieves identical recessive alleles resulting in expression of a nondominat trait. Multifactorial transmission: Combination of genetic and environmental factors to produce certain complex traits.

Mechanisms Of Heredity Patterns of Genetic Transmission When an offspring receives alleles for two contradictory traits, only one of them, the dominant one, shows itself The expression of a _______________ trait occurs only when a person receives the recessive allele from both parents

Dominant and recessive inheritance

Can you … Explain why no two people, other than monozygotic twins, have the same genetic heritage? Explain why it is the sperm that determines a baby's sex? Tell how dominant inheritance and recessive inheritance work, and why most normal traits are not the products of simple dominant or recessive transmission?

Genotypes and Phenotypes: ___________________: Observable characteristics of a person ___________________: Genetic makeup of a person, containing both expressed and unexpressed characteristics.

Nature and Nurture Studying the Relative Influences of Heredity and Environment If heredity is an important influence on a particular trait: __________ should be more alike than cousins with regard to that trait monozygotic twins should be more alike than _______________ twins __________ children should be more like their biological than their adoptive parents

Nature and Nurture Some Characteristics Influenced by Heredity and Environment Monozygotic twins generally look alike; they are also more concordant than dizygotic twins in their risk for such medical disorders as _________________ (high blood pressure), heart disease, stroke, rheumatoid arthritis, peptic ulcers, and ___________

Some Characteristics Influenced by Heredity and Environment _________________ children's IQs are consistently closer to the IQs of their biological mothers than to those of their adoptive parents and siblings Analysis of five major groupings of traits— ____________________, neuroticism, conscientiousness, agreeableness, and openness to experience—suggest a heritability of about 40 percent Nature and Nurture

Some Characteristics Influenced by Heredity and Environment ______________________ Intelligence and School Achievement ______________________ Psychopathology Schizophrenia Autism Depression

What practical difference does it make whether a trait such as obesity, intelligence, or shyness is influenced more by heredity or by environment, since heritability can be measured only for a population, not for an individual?