Name_____________________
Date___________ Class Pd___
Punnett Square Worksheet
A Punnett Square is a tool used to predict the possible genotypes for the offspring of two known parents.
Parent’s Genes
Parent’s Gene
Alleles: Different forms of a trait that a gene may have, ex: T for tall or t for short
Genotype: The letters that make up the individual. (What genes it has) E.g. TT or Tt
Phenotype: The physical characteristics of the particular trait.(What it looks like) E.g. Tall or short
Dominant trait: Represented by capital letter-E.g. T. If the traits you are using are dominant or recessive, this
trait will "overpower" the recessive trait and will be expressed. E.g. Tt expressed.
Recessive trait: Represented by small case letter-e.g. t. An organism with a recessive allele for a particular
form of a trait will have that form only when the dominant allele for the trait is not present. E.g. t is
“covered up”
Homozygous: Has same letters. E.g. TT or tt (same alleles for trait)
Heterozygous: Has different letters. E.g. Tt (different alleles for trait)
Monohybrid Cross: Also known as a Single-Factor Cross. Only one trait is used in the genetic cross. E.g.
T=Tall, t=short. Example: Tt x Tt
Ratio: The relationship in numbers between two or more things. E.g. you have 4 boys in your family and 2 girl
is a 2:1 ratio of boys to girls.
Punnett Squares Practice
Directions: Use Punnett Square to answer the following questions. Show your work.
1. Short hair (S) is dominant to long hair (s) in mice. Do a cross for a homozygous recessive female and a
heterozygous male.
2. Purple flowers (P) are dominant to white flowers (p) in pea plants. Do a cross for a homozygous
dominant female and a heterozygous male.
3. Brown hair (B) is dominant to gray (b) hair in mice. Do a cross for a homozygous recessive female and
a homozygous recessive male.
4. Green peas(G) are dominant to yellow(g) peas. Do a cross and determine the genotype and
phenotype ratios for a heterozygous female and a heterozygous male.
5. Tall plants(T) are dominant to short(t) plants. Do a cross and determine the genotype and phenotype
ratios for a heterozygous female and a homozygous dominant male.
genotype ratio ______:_______ of ______________ to _____________
phenotype ratio _____:_______ of ______________ to ______________
Do a Punnett Square to show a cross between the chromosomes of a male (xy) and female (xx)
What is the ratio of having a baby boy to baby girl? ______:______