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Grade 8 Punnett Squares & Crosses Worksheet with Answers

Grade 8 (US) · Year 9 (UK) · Class 8 (India) · Science

Unit 6: Going FurtherAdvanced: High School PreviewNGSS HS-LS3-3Advanced

Predicting offspring with Punnett squares and working out genotype and phenotype ratios. This free middle school worksheet has 12 questions and a full answer key. Print it or save it as a PDF — every answer is checked by code, not guessed.

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Punnett Squares & Crosses

Grade 8 · Science

Score___ / 12

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Class

Date

Learning goal: Advanced: High School Preview · NGSS HS-LS3-3

Directions: Read each question carefully and write your answer on the line. Use the diagram to help you.

Example

In rabbits, the allele for brown fur (B) is dominant over the allele for white fur (b). What trait does a Bb rabbit show?

Answer: brown fur

RememberGenetics words

B dominantshows if presentcapital letterb recessiveshows only as bblower-case letterBB, bbhomozygoustwo the sameBbheterozygousone of eachGenotypethe letters: BbPhenotypewhat you see: brown
  1. 1

    Cross WW × ww. What percentage of offspring are expected to show the dominant trait?

    WWww
  2. 2

    Cross Bb × Bb. What percentage of offspring are expected to show the dominant trait?

    BbBb
  3. 3

    Cross tt × TT. What is the expected ratio of dominant to recessive phenotypes?

    ttTT
  4. 4

    Cross RR × RR. What percentage of offspring are expected to show the dominant trait?

    RRRR
  5. 5

    Use a Punnett square to cross PP × PP. What is the expected genotype ratio (out of 4)?

    PPPP
  6. 6

    Use a Punnett square to cross BB × Bb. What is the expected genotype ratio (out of 4)?

    BBBb
  7. 7

    Use a Punnett square to cross WW × ww. What is the expected genotype ratio (out of 4)?

    WWww
  8. 8

    Cross Tt × Tt. What is the expected ratio of dominant to recessive phenotypes?

    TtTt
  9. 9

    Use a Punnett square to cross Bb × Bb. What is the expected genotype ratio (out of 4)?

    BbBb
  10. 10

    Cross TT × TT. What percentage of offspring are expected to show the dominant trait?

    TTTT
  11. 11

    Cross Rr × Rr. What is the expected ratio of dominant to recessive phenotypes?

    RrRr
  12. 12

    Cross Pp × pp. What percentage of offspring are expected to show the dominant trait?

    Pppp

★ Challenge corner for fast finishers

You are in a closed room with a candle, a match and a lamp. What do you light first?

How did I do?

Teacher's comments

Free printable worksheets with answer keys · aethelsystems.com/worksheets/science/8/genetics_punnett

Answer key (click to show)
  1. 1.100%
  2. 2.75%
  3. 3.all dominant (4 : 0)
  4. 4.100%
  5. 5.4 PP
  6. 6.2 BB : 2 Bb
  7. 7.4 Ww
  8. 8.3 : 1
  9. 9.1 BB : 2 Bb : 1 bb
  10. 10.100%
  11. 11.3 : 1
  12. 12.50%
  13. ★the match (challenge corner)

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Guides for teaching Punnett Squares & Crosses

Punnett Squares Step by Step (with Practice Problems)How to set up a monohybrid cross, read genotype and phenotype ratios, and work backwards from offspring to parents.How the Circulatory System Works: A Guide for Grades 5–8The heart, blood and blood vessels in plain language — the path blood takes, what each part does, and the questions students most often get wrong.

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