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chapter 3

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  • 1. Prepared by Madeleine Lacefield Tattoon, M.A.
    1
    Part I
    Heredity and Environment
    Chapter Three
    The Genetic Code
    From One Cell to Many
    From Genotype to Phenotype
    Chromosomal and Genetic Abnormalities
  • 2. 2
    The Genetic Code
    “Genes play a leading role in the drama of human development, yet they rarely take center stage. Genes are pervasive and powerful, but they are also hidden and elusive.”
  • 3. 3
    What Genes Are
    DNA (deoxyribonucleic acid)
    Molecule that contains the chemical instructions for cells to manufacture various proteins.
    Chromosome
    a molecule of DNA that contains the instructions to make proteins
    Humans have 46 chromosomes (23 pairs), and about 25,000 genes.
    Genome
    the code for making a human being
    Every person has a slightly different code, but the human genome is 99.5% the same for any 2 people.
  • 4. 4
    What Genes Are
    Genes are as section of chromosomes and the basic unit for the transmission of heredity, consisting of a string of chemicals that code for the manufacture of certain proteins.
  • 5. 5
    The Beginnings of Life
    “…development begins at conception…each human reproductive cell or gamete, contains 23 chromosomes, half of that person’s 46…”
    gamete
    A reproductive cell; that is, a sperm or ovum that can produce a new individual if it combines with a gamete from the other sex to make a zygote
  • 6. 6
    The Beginnings of Life
    Matching Genes
    conception occurs in the usual way
    zygote
    the single cell formed from the fusing of two gametes, a sperm and an ovum
    genotype
    An organism’s entire genetic inheritance, or genetic potential
  • 7. 7
    The Beginnings of Life
    Male or Female?
  • 8. 8
    From One Cell to Many
    phenotype
    the observable characteristic of a person, including appearance, personality, intelligence, and all other traits
  • 9. 9
    From One Cell to Many
    New Cells, New Functions
    Gene-Gene Interactions
    occurs through cell differentiation, gene-gene (polygenic), and gene-environment interaction
    Multifactorial
    refers to a trait that is affected by many factors, both genetic and environmental
    The Human Genome Project is an international effort to map the entire human genome
    researchers have found that humans have only about 25,000 genes, 99% of which are present in the genomes of other creatures as well
  • 10. 10
    From One Cell to Many
    Additive Heredity
    an allele is a slight, normal variation of a particular gene
    some alleles are…
    additive genes combine to make a phenotype
  • 11. 11
    From One Cell to Many
    Dominant-Recessive Heredity
    the interaction of a pair of alleles in such a way that the phenotype reveals the influence of one allele (the dominant gene) more than that of the other (the recessive gene)
    a special case of the dominant-recessive pattern occurs with genes that are x-linked, located on the x chromosome
  • 12. 12
    From One Cell to Many
    More Complications
    A small alteration in the sequence of base pairs or several extra repetitions in one triplet ma be inconsequential or may cascade to create a major problem
  • 13. 13
    From One Cell to Many
    Twins, Clones, Assisted Reproduction (ART)
    dizygotic (fraternal) twins
    result from two sperm penetrating two ova, and share 50% of their genes
    monozygotic (identical) twins
    originate from one zygote, and share 100% genes
    a clone
    originates from a live organism
    ART
    general term for the technique designed to help infertile couples conceive and then sustain a pregnancy
  • 14. 14
    From One Cell to Many
    Assisted Reproduction (ART)
    general term for the technique designed to help infertile couples conceive and then sustain a pregnancy
  • 15. 15
    From Genotype to Phenotype
    Scientist in many nations have studied thousands of twins, both monozygotic and dizygotic, raised together in the same home and raised separately in different homes
  • 16. 16
    From Genotype to Phenotype
    Genes affect every aspect of human behavior, including social and cognitive behavior
    Most environmental influences on children raised in the same home are not shared
  • 17. 17
    From Genotype to Phenotype
    Each child’s genes elicit other people’s responses, and these responses shape development. In other words, a child’s environment is partly the result of his or her genes.
    Children, adolescents, and especially adults choose environments that are compatible with their genes (called niche-picking), and thus genetic influences in adulthood
  • 18. 18
    From Genotype to Phenotype
    Carrier
    a person whose genotype includes a gene that is not expressed in the phenotype…such an unexpressed gene occurs in half of the carrier’s gametes and thus is passed on to half of the carrier’s children, who will most likely be carriers, too…
    Generally, only when the gene is inherited from both parents does the characteristic appear in the phenotype.
  • 19. 19
    From Genotype to Phenotype
    Addiction
    …inherited biochemistry making people vulnerable to various addition…
    …any one can abuse drugs or alcohol…but genes create an addictive pull that can be overpowering, extremely weak, or somewhere in between…
  • 20. 20
    From Genotype to Phenotype
    Visual Acuity
    New borns cannot focus more than 2 feet away
    Children see better each year until about age 8
    Many adolescents become nearsighted when eyeball shape changes
    Vision is more likely to improve than to worsen until age 40
  • 21. 21
    From Genotype to Phenotype
    Visual Acuity
    In middle age, the elasticity of the lens decrease and the eyeball shape change again, so that many people become farsighted and need reading glasses
    Among the old, eye diseases, including cataracts, are common
    About 10 percent of people over age 90 are blind
  • 22. 22
    From Genotype to Phenotype
    Nearsightedness and Genes
    If children have a vision problem it is most often myopia (nearsightedness)
    Nearsightedness is a symptom in more than 150 genetic syndromes
    Caused by physical trauma or illness, such as the rubella virus, or poor nutrition (such as vitamin A deficiency
    These factors cause “high” nearsightedness, so severe that it can lead to blindness
  • 23. 23
    From Genotype to Phenotype
    Culture and Cohort
    genes are not the major cause of poor vision
    historical and multicultural research finds that environment also influences nearsightedness
    if diet is deficient of vitamin A
  • 24. 24
    From Genotype to Phenotype
    Practical Application
    developmental application of nature-nurture interaction
    family history of genetic problems
    someone inherited a problem
    alcoholism in the genes
    lack of outdoor play
  • 25. 25
    From Genotype to Phenotype
    Practical Application
    type 2 diabetes (adult-onset diabetes)
    a chronic disease which the body does not produce enough insulin to adequately metabolize carbohydrate (glucose)… it typically developed in people aged 50 - 60…today it often appears in younger people
    begins when a person is vulnerable and has more body fat than is ideal
  • 26. 26
    From Genotype to Phenotype
  • 27. 27
    Chromosomal and Genetic Abnormalities
    abnormalities caused by identifiable problems…those with an extra chromosome or a single gene
    study of these problems is relevant to the study of development…
    providing insight into the complexities of nature and nurture
    knowing their origins helps limit these effects
    information combats the prejudice that surrounds such problems
  • 28. 28
    Chromosomal and Genetic Abnormalities
    Not Exactly 46 Chromosomes
    a variable that most often correlates with chromosomal abnormalities is the age of the mother
    occur not only in the formation of gametes but also in their early duplication
    mosaic is having a condition (mosaicism) that involves having a mixture of cells, some normal and some with an odd number of chromosomes or a sense of missing genes
  • 29. 29
    Chromosomal and Genetic Abnormalities
    Down Syndrome
    a condition in which a person has 47 chromosomes instead of the usual 46, with three rather than two chromosomes at the 21st position
    people with Down Syndrome typically have distinctive characteristics, including unusual facial features, heart abnormities, and language difficulties
  • 30. 30
    Chromosomal and Genetic Abnormalities
    Abnormalities of the 23rd Pair
    humans have at least 44 autosomes and one X chromosome
    an embryo cannot develop without an X chromosome
    an odd number of X chromosomes impairs cognition and psychosocial development and sexual maturation
    if a child has three sex chromosomes instead of two he/she may seem normal until puberty
  • 31. 31
    Chromosomal and Genetic Abnormalities
    Dominant-Gene Disorders
    everyone carries genes or alleles that could produce serous diseases or handicaps in the next generation
    7,000 single-gene disorders
    their dominant effects are apparent in the phenotype
  • 32. 32
    Chromosomal and Genetic Abnormalities
    Fragile X Syndrome
    a genetic disorder in which part of the X chromosome seems to be attached to the rest of it by a very thin string of molecules
    the actual cause is too many repetitions of a particular part of a gene’s code
  • 33. 33
    Chromosomal and Genetic Abnormalities
    Recessive-Gene Disorder
    most recessive disorders are not X-linked
    double recessive patterns are lethal…one recessive gene is protective
    sometimes a person who carried a lethal gene has many descendants who marry each other… the genetic disease then becomes common in that group
  • 34. 34
    Chromosomal and Genetic Abnormalities
    Genetic Counseling and Testing
    consultation and testing by trained experts that enable individuals to learn about their genetic heritage, including harmful conditions that they might pass along to any children they may conceive
  • 35. 35
    Chromosomal and Genetic Abnormalities
    Who Should Get Counseling, and When?
    genetic counseling
    consultation and testing by trained experts that enable individuals to learn about their genetic heritage, including harmful conditions that they might pass along to any children they may conceive
  • 36. 36
    Chromosomal and Genetic Abnormalities
    Is knowledge Always Power?
    Genetic counselors, scientist, and the general public usually favor testing
    having some information is better than having none
    high risk individuals (who might hear bad news) do not always want to know
    the truth might jeopardize their marriage, their insurance coverage, or their chance of parenthood
  • 37. 37
    Chromosomal and Genetic Abnormalities
    Coping with Uncertainty
    much is uncertain in genetic testing and counseling
    those who learn that they have a harmful dominant gene have new information, as well as new uncertainties
    interaction of genes and the environment makes development overt the life span unpredictable, even if the genes are known

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