Punnett Squares: Pea Plant Crosses

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Science · Biology
SP-BIO-008 · Free to print and use in your classroom · substituteplans.com
Page 2
Punnett Squares: Pea Plant Crosses
Science · Biology · Grades 9-10 · 50 minutes
Time needed
50 minutes (one class period)
Prep
Copy the 2-page worksheet (one per student). Calculators are optional.
Technology
Optional: calculators.
Student
independence
High. Individual practice with a partner check.
Copies to make
One 2-page worksheet per student
Materials
Pencils, Worksheet
Goal for today: Students will complete monohybrid Punnett squares, give genotype ratios and phenotype
percentages, and predict expected offspring numbers.
Before the bell
☐ Copy the worksheet, one per student (2 pages).
☐ Write on the board: T = tall (dominant). t = short (recessive). To fill a Punnett square, copy each parent’s
letter down the side or across the top, then combine letters in each box.
☐ Keep the answer key on your desk. Calculators are optional.
Say this to start
Today we predict what the offspring of pea plants will look like. Each parent passes one copy of a gene to its young,
and a Punnett square helps us see every possible combination. I will do one box with you, and then you will do the rest
on your own. All the rules are on the board and your worksheet.
Run of show
Minutes
What you do
What students do
0–5
Take attendance. Hand out the worksheet and read the
directions aloud.
Look over the worksheet.
5–12
Read the passage aloud. On the board, show the first box
of Cross 1: top-left T and side-left T make TT.
Follow along and fill in the first box.
12–24
Tell students to complete Part A (vocabulary, questions
1–4).
Fill in the blanks using the word bank.
24–40
Tell students to complete the three Punnett squares and
questions 5–12. Walk the room and check that each box
has two letters.
Fill in the squares and answer the
questions.
40–46
Read the square answers and questions 5–12 aloud from
the key. Students check their own work.
Correct mistakes in a different color.
46–50
Collect the worksheets and place them in a stack for the
teacher.
Hand in the worksheet.

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Science · Biology
SP-BIO-008 · Free to print and use in your classroom · substituteplans.com
Page 3
If things go wrong
• If students mix up genotype and phenotype: genotype is the letters (like Tt), and phenotype is the look (tall or
short).
• If a student writes tT, tell them it is fine, but we usually write the capital letter first (Tt).
• If a student finishes early, ask them to check that each square’s four boxes add up to 100%, then use the
early finisher list.
• If the room gets loud, move to silent work for five minutes.
Early finishers
• Make up a cross between two pea plants that would produce only tall offspring and prove it with a Punnett
square on the back.
• Choose a different trait (such as seed shape: R round, r wrinkled) and write a cross with its expected results.
Support and challenge
• Support: Let students use the board example to fill in every box with a partner before doing it alone.
• Challenge: Ask students to find which parent cross would produce a 3:1 ratio of tall to short and explain why.
Notes for the teacher (you fill this in)
Jot a few lines before you leave. A full Daily Sub Report is in the free Sub Survival Kit at SubstitutePlans.com.
How far the class got / what to pick up next:
Students who were especially helpful:
Anything the teacher should know: