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warm up
  • A green-leafed plant (LL) is crossed with a plant with yellow leaves(ll).  The cross produces the F1 generation: 185 green-leafed plants. (a) What is the genotype ratio of the 185 green leafed plants?(b)Give the genotype & phenotype ratio of the offspring that would be produced by crossing two of the F1 green-leafed plants obtained from the initial cross.
  • Mendel found that crossing wrinkle-seeded plants (ww) with pure round-seeded plants (WW) produced only round-seeded plants.What genotypes & phenotypes can be expected from a cross of a wrinkle-seeded plant & a plant heterozygous for this trait ? (include ratios for each)
ch 11 3 exploring mendelian genetics
Ch. 11-3 Exploring Mendelian Genetics
  • Objectives:
  • Explain the principle of independent assortment.
  • Describe the inheritance patters that exist aside from simple dominance.
  • Explain how Mendel’s principles apply to all organisms.
independent assortment
Independent Assortment
  • The law of independent assortment – the inheritance of one trait does not influence the inheritance of another trait.
    • For example, the alleles for seed color have no effect on the alleles for seed shape.
    • Mendel discovered this with a Two-Factor Cross

RRYY x rryy

(Round Yellow) x (Green wrinkled)

R = Round

r = wrinkled

Y = Yellow

y = green

independent assortment cont
Independent Assortment (cont.)
  • F1 plants (RrYy) were crossed with each other to determine if the alleles would segregate from each other in the F2 generation.
    • RrYy ×RrYy
    • Independent assortment would mean the new combinations of phenotypes would be seen.
    • If independent assortment were not true only the original phenotypes would be observed.
independent assortment cont1
Independent Assortment (cont.)

Mendel’s results: 9 : 3 : 3 :1 ratio in the F2 generation.

patterns of heredity can be complex
Patterns of Heredity can be Complex
  • Polygenic trait – a characteristic controlled by more than one gene.
    • Many different phenotypic combos are seen in offspring. The effect of one gene is difficult to trace.
    • Ex. Height, weight, skin, and hair color.
patterns of heredity can be complex1
Patterns of Heredity can be Complex
  • Incomplete Dominance – phenotype is intermediate between two parents.
    • Ex. Flower color in “Four O’Clock plants”: Red and white flowered parents produce pink offspring.
patterns of heredity can be complex2
Patterns of Heredity can be Complex
  • Codominance – Two alleles are expressed at the same time and both traits are seen.
    • Ex. Roan horses: Have both red and white hairs. 1 parent = red, other parent = white.
patterns of heredity can be complex3
Patterns of Heredity can be Complex
  • Multiple alleles – some genes have three or more alleles for one trait.


C = full color; dominant

to all other alleles

cch= chinchilla; partial defect in pigmentation; dominant to ch and c alleles

ch = Himalayan; color in certain parts of the

body; dominant to

c allele

c = albino; no color;

recessive to all other


Full color: CC, Ccch, Cch, or Cc

Chinchilla: cchch, cchcch, or cchc

Himalayan: chc, or chch

AIbino: cc

patterns of heredity can be complex4
Patterns of Heredity can be Complex
  • Traits influenced by environment:
    • An individual’s phenotype often depends on conditions in the environment.

Ex. 1 hydrangea flower color of blue to pink depends on the acidity of the soil.

Ex. 2 The artic fox’s coat color depends on the temperature: warm temps produce enzymes that cause a darker coat color. Therefore white in winter to blend in with the snow!

Ex. 3 Human height is influenced by nutrition

  • Read the section on p. 272 titled “A Summary of Mendel’s Principles” and summarize Mendel’s four principles in your notebook.
  • Complete Cornell Notes
  • Ch. 11-3 RSW
  • Study your Flashcards!!
mendel s principles and complex patterns of heridity
Mendel’s Principles and Complex Patterns of Heridity
  • Read pp. 272-274
    • summarize Mendel’s four principles in your notebook
    • Explain with an example the following: Incomplete Dominance, Codominance, Multiple Alleles, and Polygenic traits.
  • Complete your Cornell Notes.
  • Complete your Ch. 11-3 RSW.
  • Study your Flashcards!