Genetic Crosses (Punnett Squares) Flashcards

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Note: We may include questions that have multiple correct answers. It's useful to remember specific examples to understand these concepts better.

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What is a Punnett square used for in genetics?

It is a grid used to predict the genotypes of possible offspring.

What information do you need before you can set up a Punnett square?

You need to know the genotype of each parent for the trait you are studying.

Where do you write the alleles from each parent in a simple Punnett square?

Write one parent’s alleles for its gametes along the top, and the other’s down the side.

How many boxes are there in a Punnett square for a single-gene cross with two alleles?

There are four boxes in a 2 by 2 Punnett square.

How do you fill in the boxes in a Punnett square?

In each box, combine one allele from the top with one allele from the side.

What does each box in a Punnett square represent?

Each box shows one possible genotype for a single offspring.

In a cross between a homozygous dominant parent (TT) and a homozygous recessive parent (tt), what genotypes appear in the Punnett square for the offspring?

All four boxes show Tt, so every possible offspring has the genotype Tt.

In a cross between two heterozygous parents (Tt × Tt), what genotypes appear in the Punnett square?

The boxes show TT, Tt, Tt and tt, so offspring can be TT, Tt or tt.

How can you use a Punnett square to estimate the chance of a certain genotype?

Count the boxes with that genotype and compare it with the total number of boxes.