Dihybrid Problems Looking at 2 traits at the same time!

Remember Mendel? Worked with 7 traits on pea plants - Ex. Height, flower color, pod shape, etc. Worked with ONLY 1 trait at a time What if he wanted to look at 2 traits at the same time? Would it change things?

Law of Independent Assortment A principle that states that genes on different chromosomes behave independently –Two traits are inherited separately –The two traits are NOT influence by one another –Example: Green/yellow peas and purple/white flower color

Dihybrid Cross A cross involving two pairs of contrasting traits (ex. seed shape and pod color) R = round seedsr = wrinkled seeds G = green podsg = yellow pods Each individual has 4 alleles (letters) this time, having 2 alleles per trait Round, Green x Wrinkled, Yellow RRGG x rrgg

Determining what the parents can pass on: We going to use the FOIL method (just like in math class) F = First O = Outer I = Inner L = Last When using FOIL, you should get one of each type of letter (ex. R & G)

Using the FOIL method Let’s take the first parent: RRGG To make this easier, pretend (R+R) (G+G) –First = RG –Outer = RG –Inner = RG –Last = RG *All allele possibilities for this parent are the same *Notice that each possibility has 1 R/r and 1 G/g…you NEVER see 2 R/r’s or 2 G/g’s together. Ex. RR or gg or Gg

Second parent FOIL rrgg –First = rg –Outer = rg –Inner = rg –Last = rg * Again we see that this parent only has 1 combo of alleles to pass on

Then make a Punnett Square We only need 1 box for this P. Square RG rg RrGg