Prenatal Development Truth or Fiction

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Chapter 2Heredity and Conception
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The Influence of Heredity on Development

• The Nature of Nature

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What Is Meant by Heredity?

• Heredity
• Defines ones nature
• Genetics
• Field within the science of biology that studies
  heredity
• Genetic influences
• Physical traits
• Behavioral traits
• Psychological disorders

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What Are Chromosomes and Genes?

• Chromosomes
• Found in cells
• 23 pairs of rod-like structures
• Genes
• Segments within chromosomes
• Regulate development of traits
• DNA
• Large strands make up genes
• Double spiral (helix)
• Composed of phosphate (P), sugars (S), and base
  pairs

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Figure 2.1 Cells, Chromosomes, and DNA
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What Happens During Cell Division?

• Mitosis
• Cell division by which growth occurs
• Strands of DNA break apart and are rebuilt
• Result is identical copies of DNA strand

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Figure 2.2 Mitosis
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What Happens During Cell Division?

• Meiosis
• Cell division by which sperm and ova are produced
• 23 chromosome pairs divide
• Result is new cell with only 23 chromosomes
• 23 pairs are autosomes
• 23rd pair determines gender X from mother and X
  or Y from father

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How Are Twins Formed?

• Monozygotic Twins (MX)
• Derived from a single zygote that has split in
  two
• Genetically identical
• Dizygotic Twins (DZ)
• Derived from two zygotes
• Share 50 of genetic material

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How Do Genes Determine Traits?

• Traits are determined by alleles
• Pair of genes
• Homozygous
• Alleles for a trait are the same
• Heterozygous
• Alleles for a trait are different

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Dominant and Recessive Traits Mendels Laws of
Heredity

• Averaging
• Effects of both alleles are shown
• Incomplete dominance and codominance
• Law of Dominance
• Dominant allele paired with recessive allele
• Dominant allele appears in child

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Figure 2.4 Transmission of Dominant and Recessive
Traits
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Table 2.1
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Chromosomal Abnormalities Down Syndrome

• Cause extra chromosome on 21st pair
• Probability increases with increased age of
  parent
• Characteristics of children
• Facial features
• Cognitive and physical deficiencies
• Adjustment of children

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Table 2.2
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Genetic Abnormalities

• Recessive gene abnormalities
• PKU (phenylketonuria)
• Sickle-Cell Anemia
• Tay-Sachs disease
• Cystic Fibrosis

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Genetic Abnormalities

• Dominant gene abnormalities
• Huntingtons disease
• Sex-linked abnormalities
• Hemophilia
• Duchenne muscular dystrophy

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Genetic Counseling and Prenatal Testing

• Genetic Counseling
• Addresses probability of genetic abnormalities

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Genetic Counseling and Prenatal Testing

• Amniocentesis
• Routine among American women over age 35
• Used to detect over 100 chromosomal and genetic
  abnormalities
• Indicates the sex of the baby
• Some risk of miscarriage

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Figure 2.6 Amniocentesis
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Genetic Counseling and Prenatal Testing

• Chorionic Villus Sampling (CVS)
• Can diagnosis abnormalities earlier than
  amniocentesis
• Slightly greater risk of spontaneous abortion
• Ultrasound
• Sonogram picture of fetus
• Beneficial in determining position of fetus
• Blood Tests
• Alpha-Fetoprotein (AFP) assay

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Heredity and the Environment

• Nature versus Nurture

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What Is the Difference Between Our Genotypes and
Our Phenotypes?

• Genotypes
• Set of traits inherited from parents
• Phenotypes
• Actual sets of traits product of genetics and
  environment

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Using Research to Sort Out the Effects of
Genetics and Environmental Influences on
Development

• Kinship studies
• Genetic closeness of relatives
• Twin Studies
• Monozygotic twins share 100 of genes
• Dizygotic twins share 50 of genes (same as other
  siblings)
• Reared together versus reared apart
• Adoption studies

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Conception

• Against All Odds

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Conception Against All Odds

• Ova
• Begin to mature at puberty
• Monthly release of mature egg into Fallopian tube
• Egg is propelled by cilia
• If not fertilized, egg is discharged in the
  menstrual flow

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Conception Against All Odds

• Sperm
• Self propelled, and smaller than ova
• Sperm with Y chromosome swim faster than sperm
  with X chromosome
• From 200 to 400 million in ejaculate only 1 in
  1,000 arrive in vicinity of ovum
• Sperm are attracted by chemical odor secreted by
  ova

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Figure 2.9 Female Reproductive Organs
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What Process Brings Together the Genes From Each
Parent?

• Only one sperm enters the zona pellucida
• Sperm secrete enzyme hyaluronidase to allow
  penetration of the zona pellucida
• When one sperm enters, the zona pellucida
  thickens, locking out other sperm
• Chromosomes from sperm and egg combine to form 23
  new pairs

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Infertility and Other Ways of Becoming
Parents What Are the Causes of Infertility?

• Major fertility problems among men
• Low sperm count
• Deformed sperm
• Low sperm motility
• Infections diseases
• Direct trauma to testes
• Causes
• Genetic factors, environmental poisons, diabetes,
  STIs, overheating testes, pressure to testes,
  aging and effects of drugs

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Infertility and Other Ways of Becoming
Parents What Are the Causes of Infertility?

• Major fertility problems among women
• Failure to ovulate
• Fertility drugs are used to cause women to
  ovulate
• Infections
• Pelvic inflammatory disease (PID)
• Endometriosis
• Obstruct Fallopian tubes
• Barriers of disorders in passageways (i.e.,
  Fallopian tubes)

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Infertility and Other Ways of Becoming
Parents How Are Couples Helped to Have Children?

• Artificial insemination
• Sperm injected into mothers uterus
• In Vitro Fertilization
• Ova and sperm are fertilized, then implanted in
  mothers uterus
• Donor IVF
• Ovum harvested from donor woman fertilized in
  vitro and implanted in recipients uterus

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Infertility and Other Ways of Becoming Parents

• Surrogate Mothers
• Surrogate substitutes bring babies to term for
  another woman
• Adoption
• Option chosen by singles and infertile couples

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Selecting the Sex of Your Child

• Cultural Folklore
• Sperm-Separation Procedures
• Preimplantation Genetic Diagnosis (PGD)
• Moral and Ethical Questions