The Developing Person Through the Life Span 8e by Kathleen Stassen Berger

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The Developing Person Through the Life Span 8e
by Kathleen Stassen Berger

• Chapter 3 Heredity and Environment

PowerPoint Slides developed by Martin Wolfger
and Michael James Ivy Tech Community
College-Bloomington Reviewed by Raquel Henry Lone
Star College, Kingwood
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The Genetic Code

• What Genes Are
• DNA (deoxyribonucleic acid)
• Molecule that contains the chemical instructions
  for cells to manufacture various proteins
• Promotes growth and sustains life

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What Genes Are

• Chromosomes
• Molecules of DNA
• DNA consists of 46 chromosomes arranged in 23
  pairs

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What Genes Are

• Genes
• Specific sections of a chromosome carry
  instructions via four chemicals.
• Chemicals organized in four pairs (A-T, T-A, C-G,
  G-C).
• Each person has about 3 billion pairs.

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What Genes Are

• Allele
• A variation that makes a gene different in some
  way from other genes for the same characteristics
• Many genes never vary others have several
  possible alleles
• Genome
• The full set of genes that are the instructions
  to make an individual member of a certain species

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The Beginnings of Life

• Gametes
• Reproductive cells (sperm and ova)
• Each consists of 23 chromosomes.
• Zygote
• Two gametes (sperm and ovum) combine and produce
  a new individual with 23 chromosomes from each
  parent.

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The Beginnings of Life
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Matching Genes

• Genes are passed down from generation to
  generation
• Genotype
• An organisms genetic inheritance, or genetic
  potential
• Unique for each organism

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Matching Genes

• Homozygous
• Two genes of one pair that are exactly the same
  in every letter of their code.
• Heterozygous
• Two genes of one pair that differ in some way.
• Typically one allele has only a few base pairs
  that differ from the other member of the pair.

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Male or Female?

• Humans usually possess 46 chromosomes.
• 44 autosomes and 2 sex chromosomes termed the
  23rd pair
• Females XX
• Males XY
• Sex of offspring depends on whether the fathers
  Y sperm or X sperm fertilizes the ovum.

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Male and Female
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The Beginnings of Life

• The zygote begins duplication and division then
  differentiation and specialization occur.
• Cells change from being stem cells, those from
  which any other specialized type of cell can
  form, to being only one kind of cell.

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Twins

• Monozygotic (identical) twins
• Originate from one zygote that splits very early
  in development
• Same genotype
• Dizygotic (fraternal) twins
• Result from fertilization of two separate ova
• by two separate sperm
• Incidence is genetic and varies by ethnicity
• and age.

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Assisted Reproduction

• Assisted reproductive technology (ART)
• a general term for the techniques that help
  infertile couples conceive and sustain a
  pregnancy
• In vitro fertilization (IVF)
• takes place outside a womans body
• involves mixing sperm with ova surgically removed
  from the womans ovary
• if a zygote is produced, it is inserted into a
  womans uterus, where it may implant and develop
  into a baby.

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From One Cell to Many

• Phenotype
• The observable characteristics of a person,
  including appearance personality, intelligence,
  and all other traits
• Intimately connected with genotype
• Almost every trait is
• polygenic (affected by many genes)
• multifactorial (influenced by many factors)

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Epigenetics

• Referring to environmental factors that affect
  genes and genetic expression

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Gene-Gene Interactions

• Human Genome Project
• International effort to map the complete human
  genetic code
• Essentially completed in 2001 analysis is
  ongoing
• Found only about 20,000 genes in humans
• Exact number is unknown

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Additive Heredity

• Additive genes
• Genes that add something to some aspect of the
  phenotype
• Effects of additive genes add up to make the
  phenotype
• Example Height is affected by the contributions
  of about 100 genes

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Dominant-Recessive Heredity

• Dominant-recessive pattern - Dominant gene is
  more influential than the recessive gene
  (non-additive).
• Dominant gene can completely control the
  phenotype with no noticeable effect of recessive
  gene.
• Genes for blood type B and Rh-positive blood are
  dominant.

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Dominant-Recessive Heredity

• Carrier a person whose genotype includes a gene
  that is not expressed in the phenotype
• Unexpressed gene occurs in half of the carriers
  gametes and is passed on to half of the carriers
  offspring
• Offspring can be carrier or express the gene in
  the phenotype (e.g. when unexpressed gene is
  inherited by both parents)

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Dominant-Recessive Heredity

• X-linked A gene carried on the x chromosome

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Alcoholism

• Alcoholism probably has a genetic basis
• Genes can cause an overpowering addictive pull in
  some people
• Environmental conditions can modify the genetic
  effects
• Nature and nurture combine to create an alcoholic

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Nearsightedness

• Termed myopia
• Low nearsightedness runs in families and is
  associated with minor variations in the Pax6 gene
• Environment also plays a role
• Increase in nearsightedness among East Asian
  schoolchildren
• Increased schoolwork may have caused
  nearsightedness in children with a Pax6 allelle

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Heritability

• Statistical term that indicates what portion of
  the variation in a particular trait within a
  particular population is inherited.
• Example 90 of the height differences among
  children of the same age is genetic.
• Environment can affect the expression of
  inherited genes.

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Not Exactly 46

• Down Syndrome (Trisomy-21)
• Three copies of chromosome 21
• Specific facial characteristics (thick tongue,
  round face, slanted eyes)
• Hearing losses, heart abnormalities, muscle
  weakness, short stature
• Slow to develop language
• Accelerated aging (cataracts, dementia, certain
  forms of cancer common at age 40)

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Gene Disorders

• Dominant-Gene Disorders
• Half of the offspring of parents with a dominant
  disorder will have the disorder.
• Most dominant disorders begin in adulthood (fatal
  dominant childhood conditions cannot be passed
  on).
• Many dominant disorders have relatively mild or
  variable symptoms.
• Tourette syndrome
• Some who inherit the dominant gene exhibit
  uncontrollable tics and explosive outbursts
• Most have milder, barely noticeable symptoms

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Gene Disorders

• Recessive Disorders
• Fragile X syndrome
• Most common form of inherited mental retardation
• Additional symptoms include muscle weakness,
  shyness, and poor social skills
• Sickle-cell trait
• Offers some protection against malaria
• African carriers are more likely than
  non-carriers to survive

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Genetic Problems
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Genetic Counseling and Testing

• Genetic Counseling
• Consultation and testing by trained professionals
• Enables prospective parents to learn about their
  genetic heritage, including harmful conditions
  that may be passed on to their offspring
• Ethical Guidelines
• Test results are kept confidential
• Decisions regarding sterilization, adoption,
  abortion, or carrying a pregnancy to term are
  made by the clients

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Genetic Counseling and Testing

• Phenylketonuria (PKU)
• Recessive condition
• Results in inability to metabolize phenylalanine
  (amino acid found in many foods)
• Buildup of phenylalanine causes brain damage,
  progressive mental retardation, and other
  symptoms
• Early testing and a special diet usually results
  in normal development