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PSY2105 (102)
Chapter 3

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David Collins

Chapter 3 Heredity and Genes ­ Genetics: study of the structure and functions of genes o Genes: segment of DNA on the chromosome that codes for the production of proteins o Chromosomes: long strand of DNA ­ Heredity: sum of inherited traits and tendencies Mechanism of Inheritance ­ Cell division o Each human contains 23 pairs of chromosome o 22 pairs are autosomes o 23 pair is the sex chromosome  X carries most genetic material, Y carries fewer genes o Cells form two groups based on function:  Body cell • Reproduce by mitosis • Form the structures of the body  Germ cells • Form the reproductive cells • Reproduce my meiosis o Forms gametes: four child cells with 23 chromosomes each • Crossing over: two chromosomes pairs exchange one chromosome each o Makes sure no two people have the same genes • During conception, sperm merges with an ovum to form a new cell containing 23 pairs of chromosomes ­ Inside the chromosome o DNA: double helix structure that carries genetic information on chromosomes  Composed of 4 bases:A-T, G-C • Called base pairs: determines coded information out by the gene  Alleles: genes for the same trait found in the same place on a pair of chromosomes o How do genes affect behaviors? Two kinds of genes  Structural genes: guide the synthesis of proteins  Regulatory genes: controls activities of structural genes • Turns structural genes on and off in response to their environment ­ The human Genome Project o Purpose: determine sequence of base pairs and to identify human genes ­ Mendel’s Studies o Said that certain traits are passed from parent to child o Phenotype: expressed or observable trait, one from each parent o Genotype: arrangement of genes underlying a trait o Principles of genetic transmission:  Theory of segregation: each inheritable trait is passed on to the offspring as a separate unit  Principle of independent assortment: traits are passed on the offspring as a separate unit o Polygenic inheritance: occurs when a trait determined by a number of genes o Incomplete dominance: happens when the dominant gene doesn’t always dominate from the recessive gene o Codominance: happens when both genes are dominant and both are expressed o Genomic imprinting: when a gene from one parent is biochemically silenced and only the gene from the other parent is expressed o Genes always function according to the environment so it can affect the way the genes are exposed. Genetic and Chromosomal Disorders ­ Hereditary Disorders: abnormal genes being passed on to offspring o Huntingon’s disease  Dominant gene  Deterioration of the nervous system and results in death o Tay-Sachs disease  Recessive gene  Nervous system deterioration, early death, paralysis o Phenylketonuria  Recessive gene  If untreated, severe intellectual disability, hyperactivity, convulsions  Disease with error of metabolism  Disease where the body cannot produce the amino acid phenylalanine  Homozygous gene for making a faulty enzyme  Treatment: restrictive diet, low in amino acid o Sickle cell anemiaASK PIYUSH o Down syndrome  Autosomal disorder  Chromosome pair 21 has a third member  Mental retardation, poor muscle tone  Most occurring chromosomal disorder  3 chromosomal patterns that produce DS: • Trisomy 21 o 3 21 chromosomes, faulty cell division • Translocation o Part of chromosome 21 breaks off and attaches itself to another chromosome • Mosaicism o When unequal cell division of chromosome 21 happens in one of the initial cell divisions after fertilization causing a mixture of two types of cells, one with 46 chromosomes and the other with 47 o X-linked traits  X-linked disorders: disorder that results from recessive genes on the x chromosome, leaving males for vulnerable • Ex. Hemophilia  Fragile X-syndrome • Caused by abnormal gene on the X chromosome  Turners Syndrome: occurs when female has only 1 X chromosome  Klinefelters: occurs when males inherit extra X chromosome Studying the
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