Download Monohybrid Crosses

Monohybrid Crosses
The Punnett Square
• A visual technique used to show all of the
genotypes of offspring that can be formed
from its parents’ gametes.
Alleles
• All diploid organisms have two alleles for each
gene since they have two copies of each
chromosome.
• When gametes are produced, they only have
one allele, since homologous chromosomes
have been separated during meiosis
Steps for Solving Monohybrid Crosses
1. Read the problem: What do you need to solve
for?
2. Write a key. Define what each letter (allele)
stands for.
3. Use the key to represent the genotype of each
parents’ gametes
4. Fill in the Punnett Square using the parents’
genotypes
5. Create potential zygote genotypes
6. Analyze zygote genotypes and phenotypes
7. Complete your answer in a full sentence
Example #1
In humans, being a tongue roller (R) is a
dominant trait over non-rollers (r). A man who is
a non-roller marries a woman who is
heterozygous for tongue rolling.
A) Describe the mother and father’s genotype and
phenotype
B) What is the probability of this couple having a child
who can roll their tongue?
Example #2
In tomatoes, red fruit (R ) is dominant over
yellow fruit (r). A plant is homozygous for red
fruit is crossed with a yellow fruit plant.
A) What are the P1 and F1 phenotypes and
genotypes?
Example #3
A brown eyed man whose mother had blue
eyes, marries a blue eyed woman. What is the
chance that this couple will have a brown eyed
child if brown eyes are dominant and blue eyes
are recessive?
Example #4
• Is it possible for two brown eyed parents to
have a blue eyed child?