Use this and your genetic worksheets as a
studyguide
Genetic Rules to Follow
Always circle or underline key words within your paragraph/word
problems. This will help you to create your genotypes, phenotypes,
males vs females etc. for your Punnett squares.
Homozygous: same capitalization (Homo means “same”)
Heterozygous: different capitalization (Hetero means “different”)
Recessive: lowercase letter
Dominant: Uppercase letter
Purebred: must have the same capitalization
Hybrid: heterozygous genotypes
Genotype: The trait represented by the letter combination
Phenotype: The description of the trait/the physical characteristic you see
Sex Linked Traits
Males: XY and carry the trait ONLY on the X chromosome
Females: XX and can carry the trait on both X chromosomes
Multiple Alleles (Blood Type)
See the Amoeba Sisters worksheet
Dihybrid Cross
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16 squares each worth 6.25%
“FOIL” each parent
FOIL (First, Outside, Inside, Last)
Incomplete Dominance
1. Genotypes are represented by an Uppercase and Lowercase letter (Rr)
2. NEITHER trait is dominant or recessive in this case
3. A mixed color or blended color is made (like when you mix red paint and white paint makes
pink)
4. The mixed color they make is heterozygous
Codominance
1.
2.
3.
4.
There are NO lowercase letters
This time both traits are expressed
Both colors are represented by uppercase letters (Purebred RR-RED and WW-WHITE )
And when both colors show they will be written as a hybrid (RW hybrid- heterozygous)
Punnett Square Rules
1. Place one parent (their genotype) on the left side of the Punnett Square and the other parent
(their genotype) on the top of the Punnett Square.
2. Next, cross them. One letter from each parent needs to be placed in the box