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Chapter 4

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Psychology 1000

Psychology 1000 Chapter 4 Notes (Genes, Evolution and Behaviour) Genetic Influences  One’s genotype affects one’s phenotype.  A chromosome is coiled DNA, and DNA only coils during mitosis; more specifically prophase. o A gene is a specific fragment of DNA; more specifically a set number of nucleotides on a chromosome.  An allele is one version of a gene which has more than one version.  Influence of genes is through the synthesis of proteins.  The environment has an influence in protein synthesis. o Gene will only show (simplified) if genes inherited are dominant. If genes inherited are recessive, they will not affect the phenotype of an individual unless the other gene inherited from the opposite parent is also recessive.  Recessive traits can be passed onto offspring even if they are not shown on phenotype; the genotype still has the allele present within their karyotype.  Some genes combine their alleles to influence one part of the phenotype (polygenic transmission).  Alternate forms of a gene that produces different characteristics are called alleles.  A locus is a certain position of an allele. o You cannot infer genotype from phenotype; due to hetero and homozygous allele differences.  (insert part about recombinant DNA techniques here)  Using a heritability co-efficient, you c2n approximately estimate the extent of variation in a particular characteristic within a group. (h )  Applies to groups, not individuals o If the alleles are homozygous, the phenotypic outcome is predictable. o If alleles are heterozygous, the dominant allele (usually) determines the phenotype. o Heritability does NOT indicate the extent to which genes are responsible for the expression of the trait. o h increasess as genetic diversity increases and decreases as environmental diversity increases. o Studies:  Bouchard: Twin Studies  Jim Lewis/ Jim Springer  Oskar Stohr/ Jack Yuef  Found out that h = 0.72 o Not saying that IQ is genetically determined, however that 72% of IQ can be attributed to genetic factors.  If a certain characteristic within a family has a high co-occurrence, then this usually points to a high degree of genetic contribution rather than environmental factors.  Genetic Disorders: o PKU  Recessive gene on autosome 12  Lack of enzyme that turns phenylalanine into tyrosine.  Eventually causes brain damage/ severe mental retardation o Tay-Sachs Disease  Recessive gene of pair 15  Lack of enzymes that break down fatty acids  Normal development, then blindness, deafness, inability to swallow, muscle atrophy, mental impairment, fatal by age of 4 o Huntington’s Chorea  Rare dominant gene on autosome 4  Offspring has 50% chance of acquiring gene  At first, clumsy, forgetful then progressive deterioration in muscle control (chorea), brain atrophy; terminal in 10-20 years.  Autopsy shows patient’s brain has enlarged ventricles and cortical degeneration. o Sex-Linked Disorders  Men are more susceptible than females  Less information on Y  Issues:  Baldness  Red-Green Colour Blindness  Hemophilia o Chromosomal Disorders  Normal is XX/Xy  Others can get XXX, XXy, Xyy, X?  Down Syndrome  Trisomy of autosome 21  Marked by: o Nervous system abnormality o Mild to moderate retardation o Shorter life expectancy o Physical appearance (Mongolism)  Due to accumulation of amyloid protein
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