Heredity and Environment

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Heredity and Environment Prenatal Development
and Birth

• Lecture 2
• Chapters 3 and 4
• Psych 1643

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Genetic Foundations

• genotype - our genetic code
• phenotype - the observable characteristics that
  are the expression of our genotype.
• Chromosomes store and transmit genetic
  information
• DNA (deoxribonucleic acid) - molecules that make
  up chromosomes
• gene - a segment of a DNA molecule
• karyotype -

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The Sex Cells

• mitosis - normal cell division, cells have full
  compliment of genetic material
• meiosis - cell division that results in cells
  that have a half compliment of genetic material
• these resulting cells are called gametes - or sex
  cells (sperm ova)
• Conception occurs when two gametes join to form
  one new cell with the entire compliment of
  genetic information (46 chromosomes) - a zygote

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Boy, Girl, or Twins?

• autosomes - first 22 pairs
• sex chromosomes - 23rd pair
• XX - female
• XY - male
• Identical - monozygotic - come from one zygote,
  which splits in two
• Fraternal - dizygotic - result when two separate
  sperm fertilize two separate ova - forming two
  genetically different zygotes
• Single births simply come from a single zygote

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Patterns of Genetic Inheritance

• alleles - genes located in a certain place on a
  chromosome (on on each of a pair)
• homozygous - child inherited two identical
  alleles from the parents
• heterozygous - child inherited two different
  alleles from the parents

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Dominant - Recessive Inheritance

• In a heterozygous situation, only one alleles
  influence is exhibited
• dominant allele - will be exhibited in a
  heterozygous situation - (capital letter)
• recessive allele - will only be exhibited in a
  homozygous situation - (lowercase letter)

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X-linked Inheritance

• occurs when a recessive gene is carried on the X
  chromosome
• males are most likely to be affected, because
  they cant get the dominant gene from another X
  chromosome
• women are generally not affected, but can be
  carriers for this type of inheritance
• this type of inheritance is responsible for
• hemophilia
• color blindness

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Polygenic Inheritance

• the type of inheritance that complex traits
  follow, where many genes are involved in
  determining the characteristic (additive pattern)
• eye color is actually a polygenic trait

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Activity - Dominant/Recessive

• G- heterozygous dark hair J- homozygous blond
  hair
• How would you write out Gilberts genotype?
• How would you write out Jans genotype?
• What is Gilberts phenotype?
• What is Jans phenotype?
• What proportion of their children are likely to
  have blond hair?

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Activity - Tongue Rolling
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Activity - X-linked Traits
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The Germinal Period

• amnion - a membrane that encloses the conceptus
  in amniotic fluid
• amniotic fluid - functions as a cushion and a
  temperature regulator
• chorion - a protective membrane that forms around
  the amnion (end of 2nd week)
• placenta - an organ that allows food and oxygen
  to reach the conceptus - it also carries waste
  products away
• umbilical cord - connects the placenta to the
  conceptus

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Period of the Embryo

• Lasts from implantation through the 8th week of
  pregnancy
• To Swell
• organogenesis.
• During this period - the embryonic disk - inner
  part of the blastocyst folds in on itself to form
  three layers

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Three Layers of the Embryo
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Period of the Fetus

• Begins at beginning of second trimester - ends at
  birth
• This period is the growth and finishing phase
  that lasts until the end of pregnancy.
• Young One
• The Third Month
• the organs, muscles, and nervous system organize
  and connect
• the external genitals are well-formed, and the
  sex of the fetus is evident

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Period of the Fetus

• The Second Trimester
• the quickening - 17-20 weeks
• endogenous -
• exogenous -
• Vernix Caseosa - protects skin from becoming
  chapped in the amniotic fluid
• Lanugo - the white downy hair helps the vernix
  stick to the skin.

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Period of the Fetus

• The Third Trimester
• The age of viability - between 22 and 26 weeks
• Growth of the fetus slows and body systems become
  more complete.
• the cerebral cortex enlarges
• fat develops under the skin
• moves into and upside-down position

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Environmental Effects on Conceptus

• teratogens - does not get passed down to the
  descendants of the conceptus
• mutagens - may get passed down to the descendants
  of the conceptus.

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Principles of Teratogenic Effects

• The susceptibility of a developing organism
  varies with the developmental stage the organism
  is in at the time of the exposure (sensitive
  period).
• Not all organisms are affected in the same way by
  exposure to a given amount of a particular
  teratogen.
• Susceptibility depends of the physiological state
  of the mother.
• The greater the concentration of teratogenic
  agents, the greater the risk of abnormal
  development.
• Levels of teratogens that can produce defects in
  the conceptus may affect the mother only mildly
  or not at all.

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