Here are the answers to your Punnett Square Practice Worksheet.
Part A: Vocabulary
1–5. Match the definitions:
1.
D (homozygous) — genotypes made of the same alleles
2.
A (alleles) — different forms of genes for a single trait
3.
B (dominant) — gene that is always expressed
4.
E (recessive) — gene that is expressed only in the homozygous state
5.
C (heterozygous) — genotypes made of two different alleles
6–9. Circle the correct examples:
*(The correct choices are listed below)*
6.
Homozygous dominant (Two capital letters):
-
AA,
KK,
TT
7.
Homozygous recessive (Two lowercase letters):
-
ee,
qq,
ww
8.
Genotypes in which dominant gene must show (Any genotype with at least one capital letter):
-
AA,
Dd,
EE,
Jj,
RR,
Ss
9.
Genotypes in which recessive gene must show (Only genotypes with two lowercase letters):
-
aa,
rr
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Part B: Punnett Squares
10. Examine the following Punnett squares and circle those that are correct.
You should circle the
first one and the
fourth one.
*
First Square (Correct): Parents are $Dd$ and $dd$. The inside boxes correctly match the outside letters ($Dd, dd, Dd, dd$).
* Second Square (Incorrect): The top parent is $DD$, but the first box shows $Dd$. It should be $DD$.
* Third Square (Incorrect): The top-left box combines $A$ and $A$, so it should be $AA$, not $Aa$.
*
Fourth Square (Correct): Parents are $Aa$ and $aa$. The inside boxes correctly match ($Aa, aa, Aa, aa$).
11. What do the letters on the outside of the Punnett square stand for?
They stand for the
parents' alleles (or the parents' genotypes). One side represents one parent, and the other side represents the other parent.
12. What do the letters on the inside of the Punnett square stand for?
They stand for the
possible offspring (or the children's genotypes).
13. Complete the four Punnett squares for corn plants.
*(Key: $N$ = Normal height, $n$ = Short height)*
Square 1: Cross $NN \times nn$
* Top: $N, N$ | Side: $n, n$
* Inside boxes: All four are
$Nn$.
* *Action:* Put an
X through all four boxes (because they are heterozygous).
Square 2: Cross $Nn \times NN$
* Top: $N, n$ | Side: $N, N$
* Inside boxes: Top row is
$NN, Nn$. Bottom row is
$NN, Nn$.
* *Action:* Circle the two
$NN$ boxes. Put an
X through the two
$Nn$ boxes.
Square 3: Cross $Nn \times Nn$
* Top: $N, n$ | Side: $N, n$
* Inside boxes: Top-left is
$NN$. Top-right is
$Nn$. Bottom-left is
$Nn$. Bottom-right is
$nn$.
* *Action:* Circle the
$NN$ box. Put an
X through the two
$Nn$ boxes. Leave the
$nn$ box empty/unshaded.
Square 4: Cross $Nn \times nn$
* Top: $N, n$ | Side: $n, n$
* Inside boxes: Top row is
$Nn, nn$. Bottom row is
$Nn, nn$.
* *Action:* Put an
X through the two
$Nn$ boxes. Leave the two
$nn$ boxes empty/unshaded.
Parent Tip: Review the logic above to help your child master the concept of punnett square worksheet 1.
