Section 5: DNA and Traits - Part C

Genetics Problems

click to find the answer to today's question Does a Punnett Square show what the offspring of a cross will be?


Before completing today's assignment watch this online video on Genetics: dihybrid crosses, this will help you complete the questions below.


  Monohybrid Cross: a cross concerned with only one trait.

        Use this link to review Monohybrid crosses link to an Internet Website (use the arrows at the bottom of the page to navigate)


Monohybrid sample problem:

  • In roses, red is dominant over white.
  • Use R for the red gene.
  • Use r for the white gene.

  • Cross two heterozygous red roses,
    Rr X Rr
  • From the Punnett Square,
    • describe the phenotype of the offspring.
      • 3/4 Red
      • 1/4 White
    • describe the genotype of the offspring.
      • 1/4 RR
      • 1/4 rr
      • 1/2 Rr
Punnett Square


Dihybrid Cross: a cross concerned with two traits. link to an Internet Website


Dihybrid sample problem:

  • In mice, black is dominant over tan and short tails are dominant over long.
  • Use B for black and b for tan.
  • Use S for short and s for long.

  • Write the genotype for a heterozygous black, short-tailed mouse.
  • Cross two of these individuals.
  • From the Punnett Square, describe the phenotype of the offspring.
    • 9/16 Black - Short
    • 3/16 Black - Long
    • 3/16 Tan - Short
    • 1/16 Tan - Long
Punnett Square


Sex linked: traits that are linked to the X and Y chromosomes.  link to an Internet Website

* Use this to learn about sex linked traits

Sex-linked traits have genes located on a sex chromosome. Genes on the X chromosome are X-linked and genes on the Y chromosome are Y-linked. When genes are X-linked, males are much more likely to show recessive traits since there is no complementary gene on the Y chromosome. Color blindness and hemophilia are examples.

Sex-influenced traits are located on autosomes, but express themselves differently in the sexes because of sex hormones. Pattern baldness is an example.











Multiple alleles traits: traits that are controlled by three or more alleles of the same gene.  link to an Internet Website

How does a person get AB blood? Is this an example of a different type of genetic mix?


Assignment 1.5c  - DNA & Traits
Scoring criterialink to a local webpage

Draw the Punnett Square required for each problem, then answer the questions about the offspring.

  1. Monohybrid cross:
    In certain trees, smooth bark is dominant over wrinkled. Cross two trees that are heterozygous for smooth bark. If there are 100 offspring produced, how many will have wrinkled bark?

  2. Monohybrid cross:
    In Mountain Boomers, link to a local picturethe genes for long tail is dominant over the gene for short tail. Use a Punnett Square to predict the result of a cross between a homozygous Long-tailed and a homozygous Short-tailed Mountain Boomer. What do the offspring look like?

  3. Dihybrid cross:
    In pea plants tall stems are dominate, short stems are recessive and round seeds are dominate while wrinkled seeds are recessive. Predict the genotypic and phenotypic ratios of the offspring for a heterozygous tall stemmed, homozygous wrinkled seeded plant and a heterozygous tall stemmed, homozygous round seeded plant.

  4. Dihybrid cross:
    In certain bacteria, an oval shape is dominant over round and thick cell walls are dominant over thin. Cross a heterozygous oval, heterozygous thick cell walled bacteria with a round, thin cell walled bacteria. Describe the phenotype of the offspring.

  5. Dihybrid cross:
    In guinea pigs, black coat color is dominant over white, short hair is dominant over long. Show the Punnett Square for a cross between a homozygous black, homozygous short-haired, guinea pig and a homozygous white, long-haired, guinea pig. What do the offspring look like?

  6. Sex linked traits
    Red-green colorblindness is inherited as a sex-linked recessive gene and is found only on the X chromosome. A person with this affliction cannot distinguish between shades of red and green due to a lack of a special protein in the color receptors of the eye. A man with normal vision marries a woman who is red-green color blind. What are their genotypes? What is the probability that their children will be colorblind?

  7. Sex linked traits
    A man with normal vision marries a woman with normal vision. Their first child is a male who is discovered to have red-green colorblindness. Two years later their second child is born. It is a girl who is also red-green colorblind. The husband accuses his wife of being unfaithful. Is there any genetic basis for his accusations? Show your answer.
  8. Multiple allele

    A woman with Type O blood and a man who is Type AB are expecting a child.  What are the possible blood types of the kid?

  9. Multiple allele

    A test was done to determine the biological father of a child.  The child's blood Type is A and the mother's is B.  Dude #1 has a blood type of O, & dude #2 has blood type AB.  Which dude is the biological father? 

Honors biology: complete 1-9 above and the following section

  1. Use this link to visit the University of Arizona's  link to an Internet Website The Biology project Monohybrid Cross problem set. Read the directions at the site carefully and complete questions 9, 11, 13. Copy each of the questions along with the work you did to get your answers on a sheet of paper or in this assignment.

  2. You know have a chance to be part of the DV genetics R&D team click on this link link to a local webpage  (pdf format) and discover what your teams task will be. Your performance will be evaluated using this rubric link to a local webpage (pdf format).

  3. Use your online text web page to complete the following investigation on genetics and inheritance.



Research Links:



  Genetics Page








A Punnett Square does not show exactly what the offspring of a cross will be. It shows the "probable" offspring.
Think of each result indicated on a Punnett Square as a percentage of the offspring. The larger the number of offspring, the closer the results will be to the prediction on the square.