AP PSYCH 6.1 The Lifespan and Physical Development in Childhood

Stages of Development

Germinal Stage

• The zygote is a fertilized egg
• It undergoes rapid cell division
• The cells have XX or XY 23rd chromosomes
  • This determines the sex, which is in turn determined by the father’s genotype
  • Sometimes the 23rd chromosomes are not either of that pair, resulting in an intersex infant
• At this stage, there is the least susceptibility to environmental influences
• This stage lasts from conception to two weeks

Abnormalities

• Phenylketonuria (PKU) is an inability to produce enzymes to digest proteins
  • This is an inherited disorder
  • Causes neurological impairment
• Down syndrome occurs due to a trisomy of chromosome 21
  • Not usually inherited, likely caused by gene copying error
  • Physical growth delays and intellectual disabilities
• Note that genotype relates to genetic characteristics and phenotype relates to physical characteristics

The Placenta

• The sac that encases a child from cellular stage to fetus
• It is also the method of delivery for nutrients from the mother to the fetus
• Whatever the mother breathes, eats, or drinks can pass through the placenta and alter the course of development
• Teratogens are any environmental agent that can reach the embryo or fetus during prenatal development and cause harm
  • Alcohol causes fetal alcohol syndrome, susceptibility to alcohol later in life, neurological and physical impairments
  • Tobacco can cause a cleft palate, and low birth weight

Embryonic Stage

• The embryo is provided nourishment and oxygen by the placenta
• Organs begin to form
• Heart begins to beat
• Central nervous system begins to develop and the neural tube closes
• This lasts two to eight weeks

Fetal Stage

• Sex organs differentiate
• Toes and fingers grow
• Hearing develops
• Lungs develop
• Brain undergoes rapid growth
• Bones and muscles develop

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