Biological and Environmental Foundations

Textbook Ch 2

The beginnings of Ontogeny

• Everyone began life as a single fertilized cell (zygote) which contained our entire genetic code
• Each of us carries a “genetic code” from our parents
• This single cell then begins to divide…

Mitosis

• All body cells (except the sperm and egg)
  • 46 chromosomes in 23 pairs
• Body cells reproduce by a process called  mitosis
  • (except sperm & egg - meiosis)
• During mitosis, the cell’s nucleus -including the chromosomes—duplicates itself and the cell divides
• 2 new cells are formed, each containing the same chromosomes, genes, and DNA as the original cell

Deoxyribonucleic acid (DNA)

• Chromosomes: thread-like structures made up of deoxyribonucleic acid (DNA)
• DNA is a complex molecule that has a double helix shape, like a spiral staircase, and contains genetic information
• Any 2 humans are 99.6% identical in their DNA!
  • Vanishing influence of ancestry

"Adam" and "Eve"

• Y-chromosome Adam: ~120-156 thousand years ago
• Mitochondrial Eve: ~150 years ago
• Before human dispersion across planet
• Subsequent "bottle necks" may explain low genetic variance in humans

 Genes & DNA

• Genes are segments of DNA
  • ~20,000 genes in the humans
• Genes direct cells to
  • reproduce themselves
  • assemble proteins (100,000  in the body)
• Proteins: the building blocks of cells and life
  • Regulators that direct the body’s processes (Mader, 2008)

Proteins, bro💪

• These 100,000 proteins, once produced, determine many physical characteristics
• Genotype is translated into the Phenotype
  • Environment
• Natural Selection: the phenotype which  “fits” the environment will successfully reproduce, passing on the genotype

Patterns of Inheritance

• Dominant and Recessive genes
  • Punnett square
  • Carriers
  • Incomplete Dominance

Sex and intersex

• 23rd pair known as "sex chromosomes". XX/XY
  • Y chromosome has sex-determining region Y (SRY) protein
  • X-linked and y-linked
• XXY: Klinefelter syndrome
• XO: Turner’s syndrome
• XXX: Triple X syndrome
• XYY: XYY syndrome
• XX SRY-positive karyotype
• XY: Androgen insensitivity

Autosomal (Non-Sex) Chromosome Diseases

• Phenylketonuria (PKU): individual cannot properly metabolize phenylalanine, an amino acid
  • Recessive
• Sickle-Cell Anemia: impairs the body’s red blood cells
  • Recessive (not typical D-R expression)
• Huntington Disease: central nervous system degeneration
  • Dominant

Studying impact of heritability

• Kinship Studies
  • Identical and Fraternal twin studies
• Limitations
  • Societal/environmental factors

How do Genes interact with the Environment?

Theories

• Reaction Range- Genes offer range of reaction to  the environment

Theories

• Reaction Range- Genes offer range of reaction to  the environment

• Canalization- restrict outcomes
• Gene-Enviro correlation

What if I told you, the environment can change genetic expression and inheritance regardless of genotype?

Tune in next time for epigenetics and prenatal development!