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Heredity and Environment

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Title: Heredity and Environment


1
Part I
Chapter Three
  • Heredity and Environment

The Genetic Code From One Cell to Many From
Genotype to Phenotype Chromosomal and Genetic
Abnormalities
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
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
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
The Beginnings of Life
  • development begins at conceptioneach human
    reproductive cell or gamete, contains 23
    chromosomes, half of that persons 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
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 organisms entire genetic inheritance, or
    genetic potential

7
From One Cell to Many
  • phenotype
  • the observable characteristic of a person,
    including appearance, personality, intelligence,
    and all other traits

8
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

9
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

10
From One Cell to Many
  • Assisted Reproduction (ART)
  • general term for the technique designed to help
    infertile couples conceive and then sustain a
    pregnancy

11
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

12
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

13
From Genotype to Phenotype
  • Each childs genes elicit other peoples
    responses, and these responses shape development.
    In other words, a childs 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

14
From Genotype to Phenotype
  • Carrier
  • a person whose genotype includes a gene that is
    not expressed in the phenotypesuch an
    unexpressed gene occurs in half of the carriers
    gametes and thus is passed on to half of the
    carriers 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.

15
From Genotype to Phenotype
  • Addiction
  • inherited biochemistry making people vulnerable
    to various addition
  • any one can abuse drugs or alcoholbut genes
    create an addictive pull that can be
    overpowering, extremely weak, or somewhere in
    between

16
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

17
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

18
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 - 60today it often appears in
    younger people
  • begins when a person is vulnerable and has more
    body fat than is ideal

19
Chromosomal and Genetic Abnormalities
  • abnormalities caused by identifiable
    problemsthose 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

20
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

21
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

22
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

23
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 genes code

24
Chromosomal and Genetic Abnormalities
  • Recessive-Gene Disorder
  • most recessive disorders are not X-linked
  • double recessive patterns are lethalone
    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

25
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

26
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

27
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

28
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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