Ch3: Mendelian Genetics

Gregor Mendel

• discovered how traits are inherited using pea plants

  • work led to transmission genetics (how genes are passed down)

true breeding strains

phenotype never changes no matter how many times you cross breed

Monohybrid Cross

• cross involving one trait (e.g., tall vs dwarf)

• true-breeding parents → F₁ generation self → F₂

Mendel’s 3 Postulates:

1. Unit factors in pairs (genes come in pairs).

2. Dominance/recessiveness (one can hide the other).

3. Segregation (genes split randomly into gametes).

Test Cross:

Use a recessive individual to test if a dominant-looking individual is homozygous or heterozygous.

Mendel’s 4th Postulate:

Independent Assortment: Genes for different traits are passed on independently.

Pedigrees:

• Show how traits pass through generations, parents connected by horizontal line, vertical = offspring

  • related parents (consanguineous) = double line

  • Circles = females, Squares = males.

  • siblings left to right in order connected w/ horizontal line

    • fraternal twins = diagonal line

    • identical twins = diagonal + horizontal

  • Shaded = shows trait.

  • Dot = heterozygous carrier.

  • generations are designated by Roman Numeral

  • deceased = diagonal line through them

  • individual for who the pedigree was made for = p

Tay–Sachs Disease:

• Recessive disease.

• Caused by missing enzyme Hex-A.

• Leads to nervous system damage due to buildup of fats in brain cells.