Punnett Squares

Gregor Mendel
Punnett Squares
Monohybrid & Dihybrid
Punnett Square
Genotypes & phenotypes
Using a Punnett Square
Predicts the likely outcomes of a
genetic cross with the alleles taken
from the parents
Shows all the genotypes that could
result from a given cross
Using Probability
Likelihood that a specific event will occur
Probability = # of one kind of possible outcomes
total # of all possible outcomes
Probability of a specific allele in a gamete
Represented as a fraction or ratio
Monohybrid Cross
Cross involving a single trait
All of the crosses involved the alleles for
one gene only
Dihybrid Cross
Di= Two
Ex: A pea that is yellow and wrinkled crossed with
a pea that is green and round
Yellow ( Y )
Round ( R )
Green ( y )
Wrinkled ( r )
Cross: round green peas and
yellow wrinkled peas
Determine the parental
Determine the gametes (FOIL method)
Combine the 2 different genes for each
parent to represent a sperm cell and an
egg cell
Set up a Punnet Square 4x4,
place one gamete set from each
parent on the top and side
Write the genotypes and phenotypes of
each offspring (ratios)
Consider this cross
A cross between two heterozygous
peas for round, yellow seeds. What
are the parents genotypes?