Punnett Squares
Grade 7 · Science · Genetics and Heredity · Kentucky, USA
Lesson Summary
Use a simple diagram to predict the possible traits of offspring.
Explanation
A Punnett square is a grid used to predict the probability of offspring inheriting certain traits. Write one parent's alleles across the top and the other parent's alleles down the side. Fill in each box by combining the alleles from the row and column. The results show all possible genotypes and their probabilities. For example, crossing Bb × Bb gives a 25% chance of BB, 50% chance of Bb, and 25% chance of bb.
Practice Questions
Q1: Cross Tt × Tt using a Punnett square. What are the possible genotypes and their ratios?
Answer: TT (25%), Tt (50%), tt (25%). The genotype ratio is 1:2:1.
Q2: In the cross Tt × Tt, what fraction of the offspring would show the dominant phenotype?
Answer: 3/4 (75%) would show the dominant phenotype (TT and Tt), while 1/4 (25%) would show the recessive phenotype (tt).
Q3: Cross Bb × bb. What percentage of offspring are expected to have the recessive phenotype?
Answer: 50%. The possible genotypes are Bb (50%) and bb (50%), so half would show the recessive phenotype.
People Also Ask
What is Punnett Squares in Grade 7 Science?+
Punnett Squares is a lesson in the Genetics and Heredity chapter of Grade 7 Science. It is part of the Kentucky, USA school curriculum and covers key concepts that students need to understand at this level.
What grade level covers Punnett Squares?+
Punnett Squares is taught in Grade 7 as part of the Science curriculum in Kentucky, USA.
How can I help my child with Genetics and Heredity in Science?+
Start with the lesson summary and explanation on this page. Practice the questions provided, then use TutorTom for personalized, step-by-step help with Genetics and Heredity topics.