dihybrid problems looking at 2 traits at the same time!
Post on 19-Jan-2018
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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 seeds r = wrinkled seedsG = green pods g = yellow pods
• Each individual has 4 alleles (letters) this time, having 2 alleles per trait
Round, Green x Wrinkled, YellowRRGG x rrgg
Determining what the parents can pass on:
• We going to use the FOIL method (just like in math class)F = FirstO = 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. SquareRG
rgRrGg
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