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1.2 - Development II.pdf

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Arnav Agarwal 2011 Development II Module 1: Introduction to Hereditary Transmission - Review -> maturation: biologically-timed unfolding of changes within an individual according to a genetic plan - Genes and environment interact to determine who one becomes Chromosomes and Genes - Zygote is formed when a sperm penetrates an ovum - Zygote: single cell containing 46 chromosomes, 23 from each parent - Chromosome: threadlike structure made from deoxyribonucleic acid (DNA) - Genes provide the chemical code for development and are contained in DNA segments - Human Genome Project: human chromosomes contain between 30 000 to 40 000 genes (about 1/3 more than a simple roundworm organism) - Zygote quickly divides at an exponential rate (2 cells -> 4 cells -> 16 cells) o Birth: billions of different cells present, each with the same 46 chromosomes inherited at conception Cell Division - Each parent can produce more than 8 million different genetic combinations from his sperm or her ova o Therefore, each couple could theoretically produce 64 trillion genetically distinct offspring o Exception: identical twins - Monozygotin twins: genetically-identical individuals originating from the same sperm and ovum (formed one zygote, split into two separate zygotes) - Dizygotic twins: not more genetically-similar than normal, originating from different sperm and ova, and start off as two different zygotes from the beginning (conception) Arnav Agarwal 2011 Arnav Agarwal 2011 Arnav Agarwal 2011 Arnav Agarwal 2011 Arnav Agarwal 2011 Arnav Agarwal 2011 Arnav Agarwal 2011 Arnav Agarwal 2011 Sex Chromosomes - Male determines the gender of the child (contrary to popular belief in the past and present) - 23 chromosomes: o 22 autosomes: similar in males and females o 23 chromosome pair: determines person’s gender  Female: XX  Always passes on X chromosome  Male: XY  Can pass X chromosome or Y chromosome o If X: female offspring o If Y: male offspring Arnav Agarwal 2011 From Genotype to Phenotype - Genotype: an individula’s inherited genes, consisting of all the genes on the 46 chromosomes an individual has - Phenotype: the expression of an individual’s genotype in terms of observable characteristics True/false, genetics: - True: children inherit DNA from their parents via chromsomes. An equal number of chromosomes are inherited from each parent. - False: fraternal (dizygotic) twins share more genes than non-twin siblings, but fewer genes than identical twins - False: an individual’s genotype is determined by their phenotype - True: chromosomes contain the DNA, forming the genes that code for various traits. From Genotype to Phenotype - Expression of genotype to phenotype for particular traits can follow one of several inheritance patterns, resulting in different phenotypic characteristics in even siblings with the same parents - Four main patterms of genetic expression: o Simple dominant-recessive inheritance o Polygenetic inheritance o Codominance o Sex-linked inheritance - Simple dominant-recessive inheritance: single pair of alleles involved in determining phenotype o Pattern of inheritance in which the expression of a trait is determined by a single pair of alleles o Allele: single pair of genes o This pair of alleles determines the phenotypic expression for a particular trait o Homozygous: two alleles are the same and have the same effect on phenotype o Heterozygous: two alleles are different and have different effects on phenotype  Both allele types are carried but only the dominant allele is expressed  The carier allele is “recessive” o Note: assumption here is that phenotypic expression is the outcome of a single gene pair; in reality, it is the outcome of many genetic factors and multiple pairs of genes (eg: eye color) Arnav Agarwal 2011 - Polygenetic inheritance: multiple genes involved in trait expression o Multiple genes determine traits like height and weight; no single gene is responsible o It is the interaction between multiple genes that determine the trait - Codominance: two dominant alleles are fully and equally expressed o The phenotype produced is a compromise between the two genes o Eg: ABO blood type proteins (humans)  Two dominant alleles (A or B)  One recessive allele (O)  When both dominant alleles are present, instead of one overpowering the other, the offspring expressed both equally (blood type AB) - Sex-linked inheritance: involves genes expressed on the X chromosome o XY male: inherits X from mother and Y from father o XX female: inherits X from mother and X from father o Some recessive genes expressed on the X chromosome cause hemophilia and color blindness o As females have two X chromosomes, phenotypic expression of the recessive allele occurs less frequently in females relative to males (only one X chromosome)  Therefore, females have less sex-linked recessive gene disorders despite being genetic carriers sometimes - Examples: o Dominant-recessive inheritance: eye color o Sex-linked inheritance: color blindness Arnav Agarwal 2011 o Codominance: blood type o Polygenetic inheritance: IQ - Review: o Dominant-recessive inheritance: one pair of genes (alleles) determines trait expression. o Sex-linked inheritance: results in traits more often expressed in males than in females. o Codominance: two alleles are both expressed, to produce an intermediate or combined phenotype. o Polygenetic inheritance: several genes contribute to the expression of a trait, often showing large variation. Module 2: The Interactionist Perspective - Nature vs. nurture debate: o Behaviorist view: nurture was all-important and an individual’s development is largely independent of genetic factors  Watson: with proper environmental control and training, any individual can be made into a doctor, musician, athlete or criminal o Genetic view: who someone becomes is largely predetermined by inherited genes and the environment has a minimal effect  Intelligent, good-looking parents = intelligent, good-looking child o Modern popular view: nature-nurture debate is obsolete; genetic and environmental influences interact to produce complex traits like intelligence (genotype isn’t a fixed plan; environment influences the plan) - Canalization principle: the genotype restricts the phenotype to a small number of possible developmental outcomes o Some developmental processes are buffered or protected from variability in the environment o Eg: infant babbling -> despite the vast range of language cultures children are born into and despite some being deaf and others being able to hear, they all babble the same; the universal phonemic sensitivity is independent of the environment  Later, cultural influences shape final phonemes that are selected to remain; each culture retains phonemes for its language but loses some phonemes for others (eg: /ja/ and /jja/ in Korean) - Range of reaction principle (important for understanding complex gene-environment interactions): genotype establishes a range of possible responses to different kinds of life experiences. o Eg: although height depends on a number of factors (eg: nutrition), the potential range across poor and optimal environmental conditions is determined by genetic factors (cannot grow infinitely tall regardless of environment) Arnav Agarwal 2011 o Therefore, the genes determine the range of potentials for different traits, and the input that you receive from your environment influences how your genotype is expressed as a phenotype - Review question: what best describes the current status of the “nature vs. nurture” debate? o Psychologists generally agree that nature and nurture interact to produce the expression of individual traits, and are now interested in the extent which nature and nurture derive individual traits. o The nature vs. nurture debate has been largely “resolved” in that we know most traits are influenced by a combination of the two. Psychologists often dissect ind
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