Download Biology Name_____________________________________

Biology
Genetics Worksheet
Name_____________________________________
Per_______________
When completing Punnett squares and probabilities, follow these steps:
A) If labels for the alleles are not provided, write down a label for each allele. You will use these
labels throughout the entire problem.
B) If the genotypes for the parents are not given, write the genotypes for each parent. You will use
these genotypes to calculate the different allele combinations that each parent could give to
their offspring
C) Draw a Punnett Square. If it’s a monohybrid cross (only one gene), it’s a 3x3 grid. If it’s a
dihybrid cross (two genes), it’s a 5x5 grid.
D) For each set of parents, along the top-row and left-column, write the possible alleles that each
parent can donate to their offspring.
a. If it’s a monohybrid cross (only one gene), each row/column will only have one allele.
b. If it’s a dihybrid cross (two genes), each row/column will have two alleles—one from
each gene.
E) Fill in the grid by combining the alleles from each parent. Each of the allele combinations in the
grid is a possible genotype for the offspring of these parents.
F) To calculate the genotype ratios, create a list of every offspring’s genotype that appears in the
Punnett squares. If a genotype appears more than once, only write it once.
G) Count the number of times these genotypes appear in the Punnett squares. Write this number
next to the genotype.
H) To calculate the phenotype ratios, go through your list of genotypes and write down each
phenotype that occurs. If a phenotype appears more than once, only write it once.
I) Count the number of times these phenotypes appear according to each genotype. Write this
number next to the phenotype.
EXAMPLE PUNNETT
SQUARES
1. Write the definition for the following vocabulary words
a. Heredity____________________________________________________________________
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b. Gamete_____________________________________________________________________
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c. Zygote______________________________________________________________________
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d. Allele_______________________________________________________________________
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e. Dominant___________________________________________________________________
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f. Recessive___________________________________________________________________
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g. Genotype___________________________________________________________________
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h. Phenotype__________________________________________________________________
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i. Homozygous_________________________________________________________________
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j. Heterozygous________________________________________________________________
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2. Complete the full Punnett Square and probabilities for each genetics problem below.
a. Seed Color: YY x yy. (Y=yellow seed, y=green seed)
b. Flower Color: Pp x pp. (P=purple flowers, p=white flowers)
c. Seed Shape: Homozygous dominant x Heterozygous. (Round is dominant to wrinkled)
d. Ear Lobes Heterozygous x Heterozygous. (Unattached is dominant to Attached ear lobe)
e. Dihybrid Cross: Pea Plant Shape and Pod color. Tall (T) plants are dominant to short (t)
plants, Green pods (G) are dominant to Yellow pods (g)
i. Male is homozygous recessive for both traits, female is heterozygous for both
traits
3. Purple flowers (P) in peas are dominant to white flowers (p). Green pea pods (G) are dominant to
yellow pea pods (g). Complete a Punnett square for the following cross then answer the questions
below: PpGg x PpGg.
a. What is the likelihood that the offspring of this pair will have:
i. A genotype of PPgg?
ii. A genotype of PpGg?
iii. A genotype of Ppgg?
iv. A phenotype of white flowers and Green pea pods?
v. A phenotype of Purple flowers and Green pea pods?