Pea Plant Punnett Squares Worksheet Answer Key

Understanding Pea Plant Genetics with Punnett Squares

Pea plants have been a cornerstone of genetics studies since Gregor Mendel’s pioneering work in the 19th century. Mendel’s laws of segregation and independent assortment can be illustrated using Punnett squares, a graphical representation of the possible genotypes of offspring from a cross between two parents. In this worksheet, we will delve into the world of pea plant genetics and use Punnett squares to predict the outcomes of various crosses.

The Basics of Pea Plant Genetics

Before diving into Punnett squares, it’s essential to understand the basics of pea plant genetics. Pea plants have several characteristics that are determined by single genes, such as:

• Flower color: Red ® or white ®
• Seed shape: Round ® or wrinkled ®
• Seed color: Yellow (Y) or green (y)
• Plant height: Tall (T) or short (t)

Each of these characteristics is determined by a pair of alleles (different forms of a gene). The capital letter represents the dominant allele, while the lowercase letter represents the recessive allele.

Creating Punnett Squares

A Punnett square is a graphical representation of the possible genotypes of offspring from a cross between two parents. To create a Punnett square, follow these steps:

1. Determine the genotype of each parent.
2. Write the alleles for each parent along the top and side of a square grid.
3. Fill in the possible genotypes of the offspring by combining the alleles from each parent.

Let’s consider an example: a cross between two pea plants with the following genotypes:

Parent 1: Rr (heterozygous for flower color) Parent 2: rr (homozygous recessive for flower color)

The Punnett square for this cross would look like this:

From this Punnett square, we can see that the possible genotypes of the offspring are:

• Rr (50%)
• rr (50%)

The probability of each genotype is calculated by counting the number of times it appears in the Punnett square and dividing by the total number of possible genotypes.

Worksheet Answer Key

Here are the answers to the Punnett squares worksheet:

1. Cross between Rr and rr
   • Possible genotypes: Rr (50%), rr (50%)
   • Phenotypes: 50% red flowers, 50% white flowers
2. Cross between YY and yy
   • Possible genotypes: Yy (100%)
   • Phenotypes: 100% yellow seeds
3. Cross between Tt and tt
   • Possible genotypes: Tt (50%), tt (50%)
   • Phenotypes: 50% tall plants, 50% short plants
4. Cross between Rr and Rr
   • Possible genotypes: RR (25%), Rr (50%), rr (25%)
   • Phenotypes: 75% red flowers, 25% white flowers
5. Cross between yy and Yy
   • Possible genotypes: Yy (50%), yy (50%)
   • Phenotypes: 50% yellow seeds, 50% green seeds

👍 Note: Make sure to calculate the probabilities of each genotype by counting the number of times it appears in the Punnett square and dividing by the total number of possible genotypes.

Understanding Punnett squares and how to use them to predict the outcomes of genetic crosses is a fundamental concept in genetics. By working through these examples and practicing creating Punnett squares, you’ll gain a deeper understanding of the principles of genetics and be able to apply them to a variety of situations.

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