Biology Unit 3: Genetics
Types of Genetic Crosses
Name _____________________________
Date ________________ Per __________
1.
Monohybrid  A cross involving ____________________________________________________. a.
Key  Use 1 Letter (Upper and Lowercase)
Ex: B= Black (dominant) b= white (recessive) b.
Number of Genotypes  3
Ex: BB, Bb, bb c.
Number of Phenotypes  2
Ex: BB or Bb = black bb = white d.
Examples  ____________________________________________________________________
2.
Codominance  A cross involving _________________________________________________.
Both alleles are expressed in a ___________________________ offspring. a.
Key  Use 2 Letters (ALL CAPITALS!)
Ex: R = Red (dominant) W = White (dominant) RW = Roan (both expressed) b.
Number of Genotypes  3
Ex: RR, WW, RW c.
Number of Phenotypes  3
Ex. RR = Red WW = White RW = Roan d. Examples  ____________________________________________________________________
3.
Incomplete Dominance  A cross when ___________________ influence the phenotype.
Results in an ____________________________________________. a. Key  Use 1 Letter (Upper & Lower Case)
Ex: S = Straight (dominant) s = Curly (recessive) Ss = Wavy (mix) b. Number of Genotypes  3
Ex: SS, Ss, ss c. Number of Phenotypes  3
Ex. SS = Straight ss = Curly Ss = Wavy d. Examples  ____________________________________________________________________

4.
Multiple Alleles  A cross involving __________________________________ for a single trait. a. Examples  ____________________________________________________________________ b. (See Blood Typing Lab)
5. X-Linkage (Sex-Linkage)  Traits that are found on the _____________________________. a.
Key  Use 1 Letter (Upper and Lowercase as a superscript on the X)
Ex: X H = Normal X h = hemophilia
NOTE: The Y chromosome carries no traits! b.
Number of Genotypes (5) & Phenotypes (4)  (male and female)
Ex: X H X H or X H X h (carrier) = normal
X h X h = hemophiliac female
X H Y = normal male
X h Y = hemophiliac male c. Examples  ____________________________________________________________________
6. Dihybrid  A cross involving ________________________________________________________ a.
Key  Use 2 Letters (Upper and Lowercase)
Ex: G = Green (dominant) g = Yellow (recessive)
T = Tall (dominant) t = Short (recessive) b.
Number of Genotypes (9) & Phenotypes (4) 
Ex: Green/Tall = GGTT, GgTt, GgTT, GGTt
Green/Short = GGtt, Ggtt
Yellow/Tall = ggTt, ggTT
Yellow/Short = ggtt c. Examples  ____________________________________________________________________