1. 5 Steps to Solving Monohybrid Crosses

2. First, analyze the problem and highlight important information
PROBLEM: Dimples are dominant over no dimples. A father is homozygous dominant for dimples and a mother is homozygous recessive for dimples. What are the chances that their child will have dimples?

3. Step 1: Choose a letter to represent a trait.
Dimples =
No Dimples = D d

4. Step 2: Write down the genotype of the parents
Step 2: Write down the genotype of the parents. Remember that each parent has 2 alleles.
Mom
Dad
d d
D D

5. Step 3: Write the genetic cross.
d d x D D

6. Step 4: Set up the Punnett Square
Step 4: Set up the Punnett Square. A Punnett Square is a chart scientists use to show all the possible combinations of alleles that can result from a genetic cross. Remember, the Punnett Square shows all the possible outcomes that any 1 child may inherit. Then next time mom and dad have another child it is a new roll of the genetic dice.

7. d d D Dd Dd D Dd Dd

8. Step 5: Determine the phenotypes and genotypes of the offspring
Step 5: Determine the phenotypes and genotypes of the offspring. Remember to label the ratios.
Genotype Ratio DD : Dd : dd express in % % DD : % Dd : % dd Phenotype Ratio: Dimples : No dimples express in % % Dimples : % No dimples 4
100 4
100

9. Independent Practice
PROBLEM: In humans, freckles are dominant over no freckles. A man heterozygous for freckles reproduces with a woman also heterozygous for freckles. What chance does their child have for no freckles?

10. **Show your work for Steps 1-5 below:
1. freckles = F no freckles = f
2. Mom = Ff Dad = Ff
3. Ff x Ff F f 4. F FF Ff ff f
5. Genotypic Ratio FF : 2 Ff : 1 ff
Genotypic Percent 25%FF : 50% Ff : 25% ff
Phenotypic Ratio freckles : 1 no freckles
Phenotypic Percent 75% freckles: 25% no freckles