1. DIHYBRID CROSSES
How many different traits will be crossed in this type of cross? 2
How many total boxes? 16
How many letters at the beginning of each row and each column? 2

2. Example of a dihybrid cross

3. 2 MAIN RULES 1. KEEP LETTERS OF EACH TRAIT TOGETHER
EXAMPLE: YySs NOT YSys
2. WITHIN EACH TRAIT, KEEP THE CAPITAL LETTER FIRST.
EXAMPLE: YySs NOT yYsS

4. SIXTEEN BOXES TO COUNT UP…THAT’S A LOT…
THIS IS WHY IT’S IMPORTANT TO ALWAYS PUT THE CAPITAL LETTER FIRST IN EACH TRAIT

5. WHEN YOU COUNT UP ALL THE GENOTYPES IN 16 DIFFERENT BOXES Tt is the same as tT but very hard to recognize to the eye when counting that they are the same.

6. PEA PLANTS
Seed Shape:
Round seeds are dominant (R)over wrinkled seeds (r).
Seed color:
Yellow seed color (Y) is dominant over green seed color (y).

7. Heterozygous round and short: Rrtt

8. Homozygous round and heterozygous tall : RRTt

9. Rrtt x RRTt RT Rt RT Rt Rt Rt rt rt RRTt RRtt RRTt RRtt RRTt RRtt RRTt

10. RESULTS Genotype: 4 RRTt: 4RRtt: 4RrTt: 4Rrtt Phenotype:
8 round and tall:
8 round and short