In snapdragons, tall plants (T) are dominant to short plants (t), and red flowers (R) are dominant to yellow flowers (r). A farmer crosses a plant that is heterozygous for both gen... In snapdragons, tall plants (T) are dominant to short plants (t), and red flowers (R) are dominant to yellow flowers (r). A farmer crosses a plant that is heterozygous for both genes to a plant that is heterozygous for both genes: TtRr x TtRr. A total of 208 offspring are produced from this cross. How many of those will be short with yellow flowers?
Understand the Problem
The question is asking to determine how many offspring will be short with yellow flowers from a genetic cross (TtRr x TtRr) involving tall/short plant height and red/yellow flower color traits. This can be approached using the principles of Mendelian genetics and a Punnett square.
Answer
$1/16$
Answer for screen readers
The number of offspring that will be short with yellow flowers is 1 out of 16.
Steps to Solve
- Identify the traits and alleles We have two traits here: plant height (tall or short) and flower color (red or yellow). We represent the alleles as follows:
- Tall (T) is dominant to short (t).
- Red (R) is dominant to yellow (r).
The parent genotypes are both TtRr.
- Set up the Punnett square Since both parents are TtRr, we will create a Punnett square for each trait. First, we find the gametes that each parent can produce:
- Possible gametes from TtRr: TR, Tr, tR, tr.
Now, we can create a 4x4 Punnett square using these gametes.
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Fill in the Punnett square Fill out the Punnett square by combining the gametes from the first parent along the top and the gametes from the second parent along the side. This gives us the combinations of traits for each offspring.
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Count the combinations for short plants with yellow flowers
- We need the phenotype that is short (tt) and yellow flowers (rr).
In the filled Punnett square, we will count how many combinations yield tt and rr.
- Calculate the proportions Now, calculate the ratio of offspring that are short with yellow flowers out of the total.
The final ratio will tell us how many out of the 16 possible combinations result in short plants with yellow flowers.
The number of offspring that will be short with yellow flowers is 1 out of 16.
More Information
In a genetic cross like this, traits are inherited independently due to Mendel's law of independent assortment. The combination of two traits (height and flower color) provides a classic example of applying Punnett squares to predict phenotype ratios.
Tips
- Miscounting the offspring in the Punnett square. Make sure to carefully consider all combinations.
- Forgetting to include both traits when assessing phenotype after filling out the Punnett square.
- Confusing the dominant and recessive traits, leading to incorrect phenotype predictions.
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