Presentation on theme: "Dihybrid Crosses Biology 30 Mrs. S. Pipke-Painchaud."— Presentation transcript:
Dihybrid Crosses Biology 30 Mrs. S. Pipke-Painchaud
Dihybrid Crosses the natural progression for Mendel was to study 2 characteristics at the same time. thus, the study of 2 pairs of contrasting traits at the same time = a dihybrid cross ex.. round yellow seeds X wrinkled green seeds
Mendel’s Fourth Law The Law of Independent Assortment During gamete formation, segregating pairs of unit factors assort independently of each other. the two traits are inherited totally independently of each other. i.e. color is inherited independently of seed shape. Example: Homozygous round green X wrinkled homozygous yellow
Solving Dihybrid Crosses Follow the steps If you were to cross a Homozygous round green X wrinkled homozygous yellow plant, what would your phenotypic and genotypic ratios be?
Step 1: Make a Key…. G= yellow g = green W = round w = wrinkled
Step 2: Give the genotypes of the parents... Step 2: Give the genotypes of the parents... Homozygous round green X wrinkled homozygous yellow plant P1 = WWgg X wwGG
Step 3: Determine the Gametes... WWgg X wwGG WWgg = Wg, Wg, Wg, Wg wwGG = wG, wG, wG, wG HINT: Foil to get the gametes
Step 4: Fill in the Punnett square... WgWgWgWg wGWwGgWwGgWwGgWwGg wGWwGgWwGgWwGgWwGg wGWwGgWwGgWwGgWwGg wGWwGgWwGgWwGgWwGg
Step 5: Answer any questions... Genotypic ratio = all WwGg Phenotypic ratio = all round yellow G= yellow g = green W = round w = wrinkled
F1 X F1 = WwGg X WwGg Remember to determine the gametes for your punnett square.
Fill in the Punnett Square WGWgwGwgWGWWGGWWGgWwGGWwGg WgWWGgWWggWwGgWwgg wGWwGGWwGgwwGGwwGg wgWwGgWwggwwGgwwgg
The PATTERN... WGWgwGwg WG WWGG WWGg WwGG WwGg Wg WWGg WWgg WwGg Wwgg wG WwGG WwGg wwGG wwGg Wg WwGg Wwgg wwGg wwgg
The Short Cut: can only be used if you have (Big little Big little X Big little Big little) BbTt x BbTt Do these fit? BBTt X BbTt BbTt x Bb tt
Try this: C= Inflated Podc = constricted pod D = Talld = dwarf The cross: a plant heterozygous for inflated pod and heterozygous tall is crossed with a another heterozygous inflated pod and heterozygous tall plant. What are the genotypic and phenotypic ratios? The parents are: CcDd x CcDd
Example: Does this fit the short cut? Yes C= Inflated Pod c = constricted pod D = Tall d = dwarf Genotypic Ratio: 1 2 1 2 4 2 1 2 1 Genotypic Ratio: 1 CCDD 2 CCDd 1 CCdd 2 CcDD 4 CcDd 2 Ccdd 1 ccDD 2 ccDd 1 ccdd Phenotypic Ratio: (D) (D) 9 (D) ® 3 ® (D) 3 ® ® 1 Phenotypic Ratio: (D) (D) 9 Inflated Tall (D) ® 3 Inflated Dwarf ® (D) 3 Constricted Tall ® ® 1 Constricted Dwarf
Now try... Refer to the assigned questions in your duotang.