Download Punnett Square Worksheet

Name:
Using Punnett Squares
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Define the parent traits and the dominant/recessive status
Determine the parent genotypes
Determine the possible gametes
Complete the cross
List offspring genotypes
Determine the ratios
List offspring phenotypes (what traits are actually displayed)
Determine their ratios
Rats with one or two brown fur alleles are brown. Rats with two Albino (white) alleles are white.
A. Cross a homozygous Brown male to a White female
Male genotype:
Sperm:
Female genotype:
Egg:
offspring genotypes & ratios:
offspring phenotypes & ratios:
B. Cross a heterozygous Brown male to a heterozygous Brown female
offspring genotypes & ratios:
offspring phenotypes & ratios:
Dihybrid Crosses: If we are crossing individuals for two separate traits, and the traits are
located on two different chromosomes, then the Punnett square can be expanded or the
probability on one square can be multiplied times the probability on the other square.
( ¼ x ½ = 1/8 ). Follow the same steps listed above.
Animal Dog Dog Body character Tail Coat Length Dominant Stumpy Short Recessive Long Long Dog Dog Ear Length Leg Length Long Short Legs Short Long Legs To determine the gametes in a dihybrid cross, use the FOIL method you learned in middle
school math.
C. Complete a dihybrid cross between a stumpy tailed, short-legged male that is
heterozygous for both traits and a long tailed (homozygous recessive), long legged
female. Define the phenotypes & genotypes of the parents, the possible gametes,
complete the Punnets square and list the genotype and phenotype ratios of offspring.
There are four possible gametes from each parent. Dihybrid crosses require a square with
16 inner boxes.)
In horses, coat color is polygenic (many genes on different chromosomes). Black horses can be
homozygous or heterozygous because the black gene is dominant. Red horses are homozygous recessive.
Coat color is also influenced by a separate gene called "dilution" or "creme." Dilution (creme) horses are
a paler color, as if their main color (red or black) has been mixed with white. Dilution turns a black into
a grullo (mouse gray color) and a chestnut (red) into a palomino (blond). Heterozygous dilution animals
are one shade lighter than the color of the non-dilute animal. Palominos and grullos are heterozygous.
Homozygous dilute animals are called "double-dilutes" and are two shades lighter and also have light
colored eyes. Homozygous dilution horses are called "cremello" when red or "smokies" when black.
When the dilution allele is not present, the horse's coat has full black or red color.
D. Complete the Punnett square, following all steps, to determine the genotype and
phenotype ratios of a cross between a grullo stallion that is heterozygous for black (black
& dilute) and a palomino mare (red & dilute.)