Genetic Inheritance
Sections
1. Punnett Square
2. Genotype vs. Phenotype
3. Codominance
4. Determining Parent Genetics
5. X-recessive
6. X-dominant
7. Independent Assortment (part 1)
8. Independent Assortment (part 2)
9. Pedigree Charts (part 1)
10. Pedigree Charts (part 2)
11. Pedigree Charts (part 3)
1. Punnett Square
Goals
Select genotypes for each cross.
Punnett Squares are useful tools for determining the probability of offspring genotypes for a given trait. Throughout this lesson you will use Punnett Squares to test crosses of a variety of traits and determine offspring probabilities. Here are some rules and concepts for using Punnett Squares.

- Every person has two copies of each gene. These are called alleles.
- A person's combination of two copies of an allele is called their genotype.
- The genotype of one parent is listed along the top of the table. The genotype of the other parent is listed along the side of the table.
- The combination of two parent genotypes in a Punnett Square is called a cross.
- Dominant traits are written in capital letters, and recessive traits are written in lowercase letters.
- The physical expression of a trait is called the phenotype.
- A dominant trait will mask the expression of a recessive trait. For example, in this section a genotype of Ff (one dominant and one recessive allele) will express a freckled phenotype.
 
Select parent genotypes for each of the following crosses
to see the probability of freckled offspring:
FF x Ff
FF x ff
Ff x Ff
Ff x ff
 
Parent 1:  
 
 
 

Parent 2:  
 
 
 

   
     
     
Freckles are a dominant trait.
F = freckles
f = no freckles
2. Genotype vs. Phenotype
Instructions
Answer the following questions about offspring genotypes and phenotypes. Use the Punnett square to help you.
Goals
Answer all questions
Submit your answers
In this section we explore the differences between genotypes and phenotypes. Though an organism may have a recessive allele in its genotype, the recessive trait will not be expressed in its phenotype if it is masked by a dominant allele.

 
Cross: FF x ff
What percentage of offspring will have Ff genotype?

Cross: Ff x ff
What percentage of offspring will carry the recessive allele?
What percentage of offspring will have freckles?

Cross: Ff x Ff
What percentage of offspring will carry the recessive allele?
What percentage of offspring will not have freckles?
 
 
 
Parent 1:  
 
 
 

Parent 2:  
 
 
 

   
     
     
Freckles are a dominant trait.

F = freckles
f = no freckles
3. Codominance
Instructions
Answer the following questions about codominant traits in offspring. Use the Punnett square to help you.
Goals
Answer all questions
Submit your answers
Some traits have multiple dominant alleles. These alleles are called codominant because they are both expressed at the same time. Often this occurs by a blending of the two types of alleles.

 
Cross: RR x WW
What percentage of offspring will have RW genotype?

Cross: RW x WW
What percentage of offspring will be red?
White?

Cross: RW x RW
What percentage of offspring will be red?
Pink?
White?
 
 
 
Parent 1:  
 
 
 

Parent 2:  
 
 
 

   
     
     
Red flowers and white flowers are codominant traits.

When both alleles are present the traits
are blended, resulting in pink flowers.

R = red
W = white
4. Determining Parent Genetics
Instructions
Use the offspring phenotypes to answer questions about the parents. Use the Punnett square to help you.
Goals
Answer all questions
Submit your answers
 
The cross of two parent plants produces 1 red, 2 pink, and 1 white offspring.
What colors (phenotypes) were the two parent plants?





What were the genotypes of the parent plants?






The cross of two parent plants produces all pink offspring.
What colors (phenotypes) were the two parent plants?





What were the genotypes of the parent plants?





 
 
 
Parent 1:  
 
 
 

Parent 2:  
 
 
 

   
     
     
Red flowers and white flowers are codominant traits.

When both alleles are present the traits
are blended, resulting in pink flowers.

R = red
W = white
5. X-recessive
Instructions
Answer the following questions using the Punnett Square to help you.
Goals
Answer all questions
Submit your answers
Hemophilia is a recessive trait found on the X-chromosome. The Y-chromosome (the male chromosome) is shorter and does not have a hemophilia allele at all. Because males only have one X-chromosome, they can express hemophilia with only one copy of the recessive trait.
 
Cross: Hh x Hy
What percentage of offspring will be female?
What percentage of female offspring will express hemophilia?
What percentage of male offspring will express hemophilia?

If 50% of both male and female offspring express hemophilia, what must the parent genotypes be?




What must the parent genotypes be if 100% of offspring express hemophilia?




If no offspring express hemophilia, which parent may have been a carrier?

 
 
 
Mother:  
 
 
 

Father:  
 
 

   
     
     
H = no hemophilia
h = hemophilia
y = male chromosome
6. X-dominant
Instructions
Answer the following questions using the Punnett Square to help you.
Goals
Answer all questions
Submit your answers
Vitamin-D resistant rickets is a dominant trait on the X-chromosome. The Y chromosome does not have an allele for this trait.
 
Cross: rr x Ry
What percentage of female offspring will express rickets?
What percentage of male offspring will express rickets?

If 50% of both male and female offspring express rickets, what must the parent genotypes be?



If 100% of female offspring and 50% of male offspring express rickets, what must the parent genotypes be?



If 100% of offspring express rickets, which parent might not have carried rickets?

 
 
 
Mother:  
 
 
 

Father:  
 
 

   
     
     
R = rickets
r = no rickets
y = male chromosome
7. Independent Assortment (part 1)
Goals
Compare the example crosses
When multiple traits are inherited, each one is passed on independently.

Test the following crosses in the multiple trait Punnett Square. Compare the offspring ratios in the multiple trait square with those in the single trait squares.
LLPP x llpp
LlPp x LlPp
 
 
Parent 1:
 
 
 

 
 
 
 

Parent 2:
 
 
 

 
 
 
 

       
       
       
       
       
This lesson requires a newer browser. Please see this page for more information.
large:small
0:0
purple:yellow
0:0
   
   
   
large:small
0:0
 
   
   
   
purple:yellow
0:0
 
 
Plant size and flower color are two independent traits.
The dominant allele is capitalized for each trait.
L = large plant
l = small plant
P = purple flowers
p = yellow flowers
8. Independent Assortment (part 2)
Goals
Answer all questions
Submit your answers
Use the Punnett square to answer the following questions.
 
 
Parent 1:
 
 
 

 
 
 
 

Parent 2:
 
 
 

 
 
 
 

       
       
       
       
       
This lesson requires a newer browser. Please see this page for more information.
large:small
0:0
purple:yellow
0:0
 
 
Plant size and flower color are two independent traits.
The dominant allele is capitalized for each trait.
L = large plant
l = small plant
P = purple flowers
p = yellow flowers


A small, yellow-flowered plant is crossed with a large, purple-flowered plant. The following offspring are produced.
What is the genotype of the small, yellow-flowered parent?


What is the genotype of the large, purple-flowered parent?





Another large, purple-flowered plant is crossed with a small, yellow-flowered plant. The following offspring are produced.
What is the genotype of the large, purple-flowered parent?



 
9. Pedigree Charts (part 1)
Instructions
Pedigree charts show family trees and indicate which family members expressed certain phenotypes. Use the pedigree chart to answer the following questions.
Goals
Answer all questions
Submit your answers
 
 

The affected individuals in this chart are colorblind.

Based on the inheritance pattern, what type of trait is colorblindness?





What is the genotype of the affected female's mother?


 
10. Pedigree Charts (part 2)
Instructions
Pedigree charts show family trees and indicate which family members expressed certain phenotypes. Use the pedigree chart to answer the following questions.
Goals
Answer all questions
Submit your answers
 
 

The affected individuals in this chart express phenylketonuria (PKU), resulting in the inability to breakdown the amino acid phenylalanine.

What type of trait is PKU?





What is the genotype of the affected females?


 
11. Pedigree Charts (part 3)
Instructions
Pedigree charts show family trees and indicate which family members expressed certain phenotypes. Use the pedigree chart to answer the following questions.
Goals
Answer all questions
Submit your answers
 
 

This pedigree chart shows a family inheritance of Huntington's Disease.

Based on the inheritance pattern, what type of trait is Huntington's disease?





What is the genotype of the first generation female?


 
12. Lesson Done
Instructions
You have completed the lesson.
You may scroll up to review the lesson.

public user
return home

© 2015 ManyLabs
Creative Commons License