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Chapter 2

Chapter 2 notes

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Mark Schmuckler

Psyb20-ch 2 Heredity and the environment Genotype: the particular set of genes that a person inherits from her parents. No one has the same genotype besides identical twins The genotype interacts with the environment in complex ways to produce the phenotype Phenotype: the observable and measurable expression of an individuals physical and behavioral characteristics The process of genetic transmission Zygote: results from the union of the male and female gamete and carries the genetic info Ovum: the egg, woman gamete is the largest human cell Sperm: the male gamete, the smallest of all human cells Chromosomes and genes -chromosomes and genes are located inside the nucleus -23 chromosomes from each of these cells join to make 23 pairs 46 total -chromosomes: they carry the genetic information that helps direct development -each chromosome is homologous -each reproductive cell contains only 23 single chromosomes instead of the usual 46, because when they join they create one cell composed of 46 during development -the gametes undergo a special form of cell division meiosis where the 23 pairs are halved -the halving process mixes the chromosomes that originate from the individuals father with the chromosomes that originated from the individuals mother -further genetic variability is added during meiosis by a process called crossing over where equivalent sections of homologous chromosomes randomly switch places -mitosis: occurs in all autosomes (chromosomes that contain matching pairs) and sex chromosomes, where a cell duplicates its chromosomes and then divides into daughter cells that have the exact same number of chromosomes as their parent cell Genes, DNA , and proteins -DNA: deoxyribonucleic acid, a molecule that stores genetic info and transmits it during the reproduction, made up of nucleotides -nucleotide: compounds of nitrogen base, a simple sugar and a phosphate group -only those with bases compatible with each other will bind together to form the staircase - adenosine (A) and thymine (T) bind and cytosine (C) and guanine (G) -portions of the chromosomes DNA, genes, are located on particular sites on the chromosome where they code for the production of certain kinds of proteins -the gene or DNA segment splits down the midd;e so that its pairs of bases are no longer joined -the free nucleotides are up to form new pairs -the resulting copy of the gene then acts as a template for building protein molecules -the proteins have different functions such as giving physical properties, some may do others jobs as triggering chemical reactions, carrying chemical messages -proteins work together to function the body Genetic influences on development Genes never work in isolation but always in combination with environmental influences. Its coded message cannot be read unless it Is embedded in an environment The transmission of traits: a basic model -principle of segregation: each inherited trait comes from ones parent as a separate unit -principle of independent assortment: inheritance of various traits occurs independently of one another -at any given genes position on two homologous chromosomes, there can be more than one form of that gene -alleles: alternative form of a gene, a gene has 2 alleles, 1 from the mother 1 from the father -if the alleles from the two parents are the same, the organism Is homozygous -if the alleles are different, the organism is heterozygous -if A represents one allele and a another, then there are clearly 3 possible combinations: AA, aa, Aa (aA) -the combination of two dissimilar alleles will produce an outcome intermediate between the traits, for which each single allele codes -both alleles will express their traits simultaneously, that is the two traits will combine but not blend. This is co-dominance as seen in blood types -a heterozygous combination the characteristics associated with only one of the alleles is expressed -the more powerful is dominant, the least is recessive -many inherited characteristics follow this dominant-recessive type of relation -many harmful alleles are recessive, which greatly reduces the incidence of genetic abnormalities Genes on the sex chromosomes: exceptions to the rule -one of 23 pairs, or two of the 46 chromosomes are called sex chromosomes -they have important function of determining the individuals gender, they differ in males and females -a female has 2 large homologous XX chromosomes-the male has XY, X from the mother and the Y from the father -X is 5 times longer than Y and so it carries more genes -x linked genes: genes that are carried on the X chromosome and that may have no analogous genes on the Y chromosome in males -hemophilia: example of x linked recessive characteristic. A female may have lesser chance because she has an extra X chromosome. For men, if it is on the X chromosome he has a greater danger of developing hemophilia -disorders are more common inn men than in women, such as certain types of blindness. And certain childhood diseases Interactions among genes -most of the characteristics that are of the greatest interest to psychologists, such as intelligence, creativity, sociability and style of emotional expression, are probably influenced by the interaction of multiple genes -development of traits depends on a certain configuration of many genes, and that particular configuration is not likely to be passed on from parent to child - a single pair of alleles may influence more than one trait -modifier genes: genes that exert their influence indirectly, by affecting the expression of still other genes -ex: nature of cataract formation is influenced by mod
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