• Tampa Catholic High School

• SCI 100

Non-Mendelian Genetics Practice Packet

Most genetic traits have a stronger, dominant allele and a weaker, recessive allele. In an individual with a

heterozygous genotype, the dominant allele shows up in the offspring and the recessive allele gets covered up and

doesn’t show; we call this complete dominance.

However, some alleles don’t completely dominate others. In fact, some heterozygous genotypes allow both alleles

to partially show by blending together how they are expressed; this is called incomplete dominance. Other

heterozygous genotypes allow both alleles to be completely expressed at the same time like spots or stripes; this is

called codominance. Examples of each are listed below.

Write what each type would be if they were heterozygous.

1. Complete dominance = If a Red (RR) and White flower (rr) were crossbred, resulting in 100% Rr, what

phenotype would been seen according to the rules of COMPLETE dominance?

2. Incomplete dominance = If a Red (RR) and White flower (rr) were crossbred, resulting in 100% Rr, what

phenotype(s) would been seen according to the rules of IN-complete dominance?

3. Codominance = If a Red (RR) and White flower (WW) were crossbred, resulting in 100% RW, what

phenotype(s) would been seen according to the rules of CO-dominance?

Incomplete Dominance Practice Problems

4-6. Snapdragons are incompletely dominant for color; they have phenotypes red, pink, or white. The red flowers

are homozygous dominant, the white flowers are homozygous recessive, and the pink flowers are heterozygous.

Give the genotypes for each of the phenotypes, using the letters “R” and “ r ” for alleles:

a. Red snapdragon b. Pink snapdragon c. White snapdragon

genotype: ______ genotype: ______ genotype: ______

Show genetic crosses between the following snapdragon parents, using the punnett squares provided, and

record the genotypic and phenotypic %s below:

a. pink x pink b. red x white c. pink x white

Genotypic Genotypic Genotypic

%: ________________ %: ________________ %: ________________

Phenotypic Phenotypic Phenotypic

%: ________________ %: ________________ %: ________________

Zachary Greif 4 1 B

red

pink

red and white

RR WW RW

R W R R R W

R RR RW W RW RW w RW WW

W RW WW w RN RW w RW WW

l3L 100 IL

I 2L 10001 I

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7-9. In horses, some of the genes for hair color are incompletely dominant. Genotypes are as follows: brown horses

are BB, white horses are bb and a Bb genotype creates a yellow-tannish colored horse with a white mane and tail,

which is called “palomino”. Show the genetic crosses between the following horses and record the genotypic and

phenotypic percentages:

a. brown x white b. brown x palomino c. palomino x palomino