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Chapter 2The Start of Life: Genetics and Prenatal

Development

© 2006 Pearson Education/Prentice-Hall Publishing

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Heredity

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Heredity

• The human genetic code is transferred by gametes.– Sperm– Ova

• The sex cells from the mother and father that form a new cell at conception (aka sperm and ovum).

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Heredity

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Fertilization = sperm + ovum (the gametes) = one set of paired chromosomes = single new cell, a zygote.

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• The 23rd chromosome determines the sex of the child.– Females are XX.

– Males are XY.

– The FATHER’s sperm determines the sex of the child.

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• Monozygotic/DizygoticSome Terms to Remember

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• Concordance rateSome Terms to Remember

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Sandra Scarr: Genetics can influence environment in 3 ways:

1. Active (niche-picking) genotype-environment effects - children seek out environments they find compatible and stimulating

2. Passive genotype-environment effects - parents raise children in the way in which they are comfortable

3. Evocative genotype-environment effects - child’s characteristics elicit certain types of environments

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• Dominant/Recessive [next]• Genotype – genetic material• Phenotype – observable• Gregor Mendel

Some Terms to Remember

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b BB bb bB B

MotherB b

FatherB b

b

B

Blond hair

Brown hair

How Brown-Haired Parents Can Have a Blond-Haired Child

The gene for blond hair is recessive.

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Some Genetic Disorders

Down Syndrome

Sickle-Cell Anemia

Tay-Sachs

Klinefelter’s Syndrome

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Behavioral Genetics

• How behavioral disorders may have a genetic basis (e.g., schizophrenia).

• How genetic defects may be remedied.• The inheritance patterns of genetic

disorders.• How physically damaged genes

contribute to genetic disorders.• Gene therapy, genes to correct a

particular disease are injected into a patient’s bloodstream

• Germ-line gene therapy, genetic modifications can correct problems for unborn AND future generations

• Cloning

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The Start of LifeAlternate forms of fertilization

(Reproductive Technology)

Artificial Insemination

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The Start of LifeAlternate forms of fertilization

(Reproductive Technology)

In vitro fertilization (IVF)

Eggs are harvested from the woman’s ovaries, fertilized in the lab, and then deposited in the uterus

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The Start of LifeAlternate forms of fertilization

(Reproductive Technology)

Gamete intrafallopian transfer

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The Start of LifeAlternate forms of fertilization

(Reproductive Technology)

Zygote intrafallopian transfer(~ IVF + GIFT)

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Success Rates of Three Different Assisted Reproduction Techniques

0

10

20

30

40

29.2%31%

24.5%

ZIFTIVF GIFT

There is little variation in success rates based on couples’ ages.

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This single cell is transformed into a person by the human genetic code.

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Zygote

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The Start of Life The Onset of Development

Germinal Stage(first two weeks)

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Germinal disc 0.8 hours post fertilization

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The Start of Life The Onset of Development

Embryonic Stage (two to eight weeks)

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Gastrulation

• Ectoderm

• Endoderm

• Mesoderm

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The Start of Life The Onset of Development

Fetal Stage (eight weeks until birth)

During the fetal period, the proportions of the body change dramatically.

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Prenatal Testing

Chorionic Villus Sampling (CVS)

Amniocentesis-- Often goes along with genetic counseling

Ultrasound Sonography

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Threats to Prenatal Development

• Illnesses• AIDS• Aspirin• Thalidomide• Marijuana• Cocaine• Cigarettes• Alcohol