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Chapter 2

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Diane Mangalindan

Chapter 2: Heredity and the Environment  The moment babies are born, they differ from each other physically and in behaviour  Transactions among a vast array of hereditary and environmental factors begin before birthbetween genes and the environment make each baby unique  What provides a framework for exploring the interactions of genes and environment is the concept of genotype and phenotype:  genotype- is the particular set of genes that a person inherits from her parents, no two people have exactly the same genotype-except identical twins; during the course of the development, the genotype interacts with the environment in complex ways to produce the phenotype  phenotype-the observable and measurable expression of an individual’s physical and behavioural characteristics, ie) motor abilities, intellectual skills, social behaviour and personality traitspsychologists study these kinds of characteristics to increase our understanding of how genetic and environmental factors interact to produce each unique human being The Process of Genetic Transmission  the sperm and the egg unite together to create a new living organism that has the potential to develop into a human being—zygote  zygote- new organism, results from the union of male and female gametes, or reproductive cells, each other which carries genetic information  ovum- (or egg) the largest human cell, is about 90 000 times as heavy as the sperm that penetrates it (smaller than the punctuation period.)  sperm- the smallest of all human cells, shape of a head, where the hereditary information is, with a whip-like tail, uses to propel itself through the woman’s reproductive system in search of the ovum  (beginning of a 9-month period that ends with a full term baby, 7 or 8lbs & ~50cm long) Chromosomes and Genes (located inside the nucleus-centre of the cell  at the moment of human conception, when the sperm and the egg unite, 23 chromosomes from each of these cells join together to create 23 chromosome pairs, or 46 chromosomes in all (1/2 from mom 1/2 from dad)  chromosomes-thread-like structures located in the centre of the nucleus that carry genetic info to help direct development  each chromosome is homologous—similar in shape & function-so pairing is possible  each reproductive cell contains only 23 single chromosomes instead of the usual 46 because during its development, it undergoes a special form of cell division, called meiosis in which its 23 chromosome pairs are halved  23 chromosomes from sperm combine with 23 chromosomes from the egg to produce the correct number of 46 chromosomes for a new human being  meiosis- a type of cell division that produces male and female reproductive cells  -both meiosis and sexual reproduction are crucial to the process of genetic transmission because each facilitates the production of a tremendous diversity of genetic combinations  -random assortment of homologous chromosomes makes possible the production of about 8 million different chromosome combinations in both the female’s eggs and the male’s sperms  further genetic variability is added during meiosis by a process called crossing overin which equivalent sections of homologous chromosomes randomly switch places so that genetic info is shuffled even more o this is why the chance of any given man and woman producing two genetically identical children is one in many trillions (except when a single fertilized egg splits to form identical twins)  by a process called mitosis, which occurs in all autosomes (chromosomes that contain matching pairs) and sex chromosomes, a cell duplicates its chromosomes and then divides into daughter cells that have the exact same number of chromosomes as their parent cell  Mitosis-the process in which a body cell divides in two, first duplicating its chromosomes so that the new daughter cells contain the usual 46 chromosomes  Autosomes-the 22 paired non-sex chromosomes  Thus the zygote divides and continues to divide, each time producing new cells that have the full complement of 46 chromosomes, and gradually becomes a multi-cellular organism Genes, DNA, and Proteins  the binding element of a chromosome is a long, thin molecule of deoxyribonucleic acid, or DNA for short  DNA-a ladder-like molecule that store genetic info in cells and transmits it during reproduction  DNA is made up of building blocks called nucleotides that are held together by two long, twisted parallel strands that resemble the two side rails of spiral staircase  Nucleotide-a compound containing a nitrogen base, a simple sugar, and a phosphate group  From each nucleotide, 4 different nitrogen-containing bases projects out towards the base on its opposite side to form one of the staircase’s risers (only bases that are compatible with each other will bond together (fig 2-3 pg 47 shows adenine and thymine form a bond, as do cytosine and guanine, but no other combinations of this 4 is possible)  Portions of the chromosome’s DNA molecule, called genesare located at particular sites on the chromosomes where they code for the production of certain kinds of proteins  Proteins- fundamental components of all living cells, and are any of a group of complex organic molecules containing carbon, hydrogen, oxygen, nitrogen and usually sulphur, and that are composed of one or more chains of amino acids Genetic Influences on Development  Scientists continue to learn about how genes exert their influences on development-central message that they discovered with respect to behaviour, genes never work in isolation, but always in combination with environmental influences  A gene alone is useless, its coded message cannot be read unless its embedded in an environment that signals when and how it should respond The Transmission of Traits: A Basic Model  much of the original work that is the basis of modern genetics was done in the 19 C by Gregor Mendel, an Austrian monk, who, from his observation of pea plants, worked out the basic principles that govern the inheritance of characteristics from one generation to the next  he spent years cross-breeding pea plants and then cataloguing the results of these hybridizations: observationsmany of the characteristics of the pea plans, such aspects as flower colour, the height of the stalks etc, varied from one generation to the next, with a trait that had been present in one generation disappearing in the next generation but, then, reappearing again in a following generation  from the observa
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