Friday January 31 2014 Developmental Psychology Chapter 3 Genetics and Heredity Nature Nurture How do nature and nurture interact in development The phenotype the observable behaviors and characteristics of an individual is the product of complex multiple factors interacting between genotype and environment Environment includes biological contexts ranging from the composition of the cells to the foods we eat but it also includes the experiences provided by caregivers and others These environmental factors influence the functioning of genes immediately after conception and continue to have an impact throughout development As a consequence experiential factors are tightly interwoven with and may even modify the operation of genes to produce the range and variety of behaviors and characteristics an individual displays Determining the relationship between genotype and environment is further complicated by passive reactive and niche picking correlations Risk Resilience What factors promote risk or resilience in development Individual differences are pervasive in intellectual temperamental and a host of other cognitive social and emotional aspects of development Hereditary and environmental factors work in combination to determine these differences Certain experiences also may turn the ability of genes on or off and therefore increase risk or resilience A distinctive combination of genes and experiences underlies both the risk and the resilience we observe in human abilities and behavior 1 Friday January 31 2014 Principles of Hereditary Transmission The genetic endowment inherited by an individual is the genotype A phenotype refers to the traits and behaviors displayed by an individual The phenotype is the result of complex multiple factors interacting between the genotype and the experiences provided in the environment The entire inventory of nucleotide base pairs that compose the genes and chromosomes in humans is called the human genome The structures associated with the principles of heredity must be examined at several different levels An individual s body is composed of trillions of cells 23 pairs of chromosomes a total of 46 consisting of deoxyribonucleic acid or DNA are located int he nucleus of most cells in the human body A central unit of hereditary information is the gene a segment of a chromosome Nucleotides are two different sets of pairs of repeating molecules that form the biochemical building blocks for the genes and the basic structure of the chromosomes The human karyotype consists of 22 pairs of autosomes one member of each pair inherited from the mother the second from the father Males and females differ in the composition of the 23rd pair of chromosomes In females both members of the pair normally are X chromosomes In males one is normally an X chromosome and the other is a Y chromosome Cell division in the human body takes place in two different ways Mitosis is the process of cell division by which the 46 chromosomes are duplicated in the body cells The gametes or sperm and egg cells are formed by meiosis a process of a cell division that results in 23 chromosomes in each of these cells The random process by which a member of each of the 23 pairs of chromosomes is selected for the gametes combined with crossing over during meiosis ensures that every individual with the exceptions of identical twins has a unique 2 Friday January 31 2014 hereditary blueprint Once the fertilized egg is called a zygote gametes combine the Variants of genes on the 23 pairs of chromosomes or alleles often interact with one another to establish probabilities of inheritance for particular traits or characteristics A dominant allele will reflect its characteristics even when it is part of a heterozygous genotype in which alleles of a gene are different A recessive allele is expressed only when it is a homozygous genotype in which two alleles of a gene are the same Codominance refers to the condition in which unblended characteristics of two alleles are reflected in the phenotype Many human traits however are polygenic that is they are influenced by many different genes Genetic information coded in DNA is recoded into mRNA a process called transcription The mRNA migrates to regions outside of the cell nucleus where the genetic information is translated into the production of proteins that result in different cell functions The field of epigenetics is concerned with identifying how environmental conditions influence these processes of transcription and translation Genomic imprinting refers to instances of genetic transmission in which the parental source of the gene from mother or father determines how the gene is expressed Gene and Chromosomal Abnormalities Mutations or spontaneous changes int he molecular structures of genes can have wide ranging influences on development from almost no consequence to death Some of these genetic or chromosomal problems can be passed from one generation to the next Williams syndrome is caused by deletion of a small number of genes on chromosome 7 The phenotypic features include a short upturned nose full lips and curvature of the knee 3 Friday January 31 2014 and hips Children with Williams syndrome display uneven developmental profiles they often have unusual skill in music and show considerable attention to social stimuli but typically have poor spatial numerical and problem solving skills Phenylketonuria PKU results from the presence of two recessive genes for the trait Untreated children with PKU may exhibit convulsions severe intellectual impairment and hyperactivity Early intervention with a modified diet can prevent many of these symptoms from manifesting themselves Sickle cell disease arises from the presence of two recessive genes that cause the red blood cells to become less efficient in transporting oxygen The result can be anemia jaundice infection and vulnerability to stroke organ damage and pain An individual with sickle cell trait has only one of the recessive alleles but may still show symptoms under conditions of low oxygen The presence of this allele provides protection against malaria Fragile X syndrome results from a constriction in one region of the X chromosome and is said to be sex linked The phenotypic will typically result in an individual having a long narrow face large ears and large testes Fragile X is the most frequently inherited source of intellectual impairment for males The inheritance of only one chromosome on the