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Copyright © 2010, Pearson Education Inc., All rights reserved. Chapter 2 Heredity and Environment

Copyright © 2010, Pearson Education Inc., All rights reserved.  Genes and Human Reproduction  How Traits and Genetic Abnormalities Are Inherited  How Genes and Environments Interact  Behavior Genetics: Measuring the Heritability of Traits

Copyright © 2010, Pearson Education Inc., All rights reserved.  In general, do you believe that traits like intelligence and personality are more inherited or more learned?  Why do you believe this?

Copyright © 2010, Pearson Education Inc., All rights reserved.  Each one of us began as a single cell – a fertilized egg cell.  Genes and the Magical Four-Letter Code  Human Reproduction and Cell Division

Copyright © 2010, Pearson Education Inc., All rights reserved.  Chromosomes ◦ Strands of deoxyribonucleic acid molecules that contain the genetic code.  DNA ◦ Two strands of molecules that twist around each other connected by a series of nucleotide bases.  Gene ◦ A segment of DNA that provides an instruction for a particular structure, function, or trait.  Human Genome Project ◦ An effort to map the nucleotide bases and genes contained in chromosomes.

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 Fertilization ◦ The union of the father’s sperm cell with the mother’s egg  Allele ◦ An alternative version of a gene; alleles operate in pairs across matched chromosomes  Zygote ◦ Human organism after egg cell begins to divide  Mitosis ◦ Copy division

Copyright © 2010, Pearson Education Inc., All rights reserved.  Meiosis ◦ Reduction division  Monozygotic (MZ) Twins ◦ Identical twins ◦ These twins form when one zygote divides  Dizygotic (DZ) Twins ◦ Fraternal twins ◦ These twins form when two eggs are fertilized by two different sperm cells  Sex Chromosomes ◦ The 23 rd pair of chromosomes specialized to determine the sex of the child

Copyright © 2010, Pearson Education Inc., All rights reserved.  Dominant-Recessive Traits  Chromosome Abnormalities  Prenatal Screening and Genetic Testing

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 Dominant-Recessive Relationships ◦ To express a recessive trait, the individual needs to inherit two recessive alleles – one on each chromosome.  Dominant Gene Diseases ◦ Individuals only need one dominant allele to inherit the trait.  Recessive Gene Diseases ◦ Individuals must inherit two recessive alleles – one from each parent – to show the trait.  X-linked (sex-linked) Traits ◦ Traits that differ in rate of occurrence between male and female.

Copyright © 2010, Pearson Education Inc., All rights reserved.  Down Syndrome ◦ A genetic disorder that occurs when there is an extra 21 st chromosome. ◦ Low IQ, facial defects, heart problems, and shortened life span.  Sex Chromosome Abnormalities ◦ Abnormalities in the number of sex chromosomes are among the most common of all human genetic disorders. ◦ Abnormalities occur in about 1 in every 500 live births.

Copyright © 2010, Pearson Education Inc., All rights reserved. Figure 2.10 Risk of Down Syndrome Due to Mother’s Age

Copyright © 2010, Pearson Education Inc., All rights reserved.  Ultrasonography (ultrasound) ◦ Images of the fetus inside the mother’s womb – produced by sound waves ◦ Used to help monitor fetal growth and detect defects  Amniocentesis ◦ Procedure used to detect chromosomal and genetic abnormalities in the fetus ◦ A needle is inserted in the mother’s abdomen and cells are withdrawn from the amniotic fluid  Chorionic Villus Sampling (CVS) ◦ A catheter is inserted into uterus and cells are taken to test. Prenatal Screening and Genetic Testing

Copyright © 2010, Pearson Education Inc., All rights reserved. Figure 2.11 Ultrasound Image of a Fetus

Copyright © 2010, Pearson Education Inc., All rights reserved. Figure 2.12 Genetic Testing During Pregnancy

Copyright © 2010, Pearson Education Inc., All rights reserved.  G x E Interaction ◦ The interacting effects of genetics and the environment on the development of traits and characteristics How Genes and Environments Interact

Copyright © 2010, Pearson Education Inc., All rights reserved.  Range of Reaction ◦ Genotype  The genetic code a person inherits ◦ Phenotype  The observable trait a person shows, resulting in part from his or her inherited genotype ◦ Range of reaction  The range of possible phenotypes that exist for a particular genotype Range of Reaction, Canalization, and Niche-Picking

Copyright © 2010, Pearson Education Inc., All rights reserved.  Canalization ◦ Genetic limits on the effects of the environment  Niche-Picking ◦ The tendency to pick activities and environments that fit with our genetic predispositions  Probabilistic Epigenesis ◦ The likelihood that specific environmental conditions will activate specific genes that lead to specific outcomes Range of Reaction, Canalization, and Niche-Picking (continued)

Copyright © 2010, Pearson Education Inc., All rights reserved. Figure 2.13 Range of Reaction for Cognitive Skills of Three Children

Copyright © 2010, Pearson Education Inc., All rights reserved.  How different are you from your siblings and parents?  What accounts for the differences and similarities?  Behavior genetics is a field that tries to answer these questions. Behavior Genetics: Measuring the Heritability

Copyright © 2010, Pearson Education Inc., All rights reserved.  Heritability ◦ Estimate of the degree of genetic influence for a given trait or behavior  Shared Environments ◦ Experiences and aspects of the environment that are common across all individuals who are living together  Nonshared Environment ◦ Experiences and aspects of the environment that differ across people Behavior Genetics, Heritability, Shared and Nonshared Environments

Copyright © 2010, Pearson Education Inc., All rights reserved.  Twin Studies ◦ Comparisons between measurements of identical and fraternal twins, used to estimate the genetic contribution to traits and characteristics  Adoption Studies ◦ Comparisons between measurements of children and their adoptive and biological parents used to estimate the genetic contribution to traits and characteristics How Is Heritability Estimated?

Copyright © 2010, Pearson Education Inc., All rights reserved.  Heritability of Cognitive Skills ◦ Probably the most extensively studied behavioral trait is intelligence. ◦ A variety of cognitive skills have a significant hereditary component.  Heritability of Personality and Temperament ◦ Genetics is an important influence on personality and temperament. Heritability of Complex Characteristics

Copyright © 2010, Pearson Education Inc., All rights reserved. Figure 2.16 Heritability of Verbal and Spatial Abilities