Free Printable Dihybrid Cross Worksheets for Students - Free Printable

Dihybrid Cross Worksheet 1 Solution and Explanation

#### Vocabulary: Fill in the Blanks
We need to match the definitions with the correct terms from the provided list.

1. A cross between parental organisms that have a variation in a single gene or trait.
- Answer: G. Monohybrid cross

2. A cross between parental organisms that differ in two different traits.
- Answer: I. Dihybrid cross

3. Square diagram used to predict genotypes of mated individuals.
- Answer: L. Punnett square

4. A basic unit of hereditary information.
- Answer: A. Gene

5. A characteristic or attribute associated with a gene.
- Answer: M. Trait

6. A variation of a gene.
- Answer: H. Allele

7. Type of allele that solely produces an observed trait.
- Answer: C. Dominant

8. An allele with masked effects.
- Answer: D. Recessive

9. Inheriting different alleles of a given gene from each parent.
- Answer: B. Heterozygous

10. Inheriting the same alleles of a given gene from each parent.
- Answer: K. Homozygous

11. The frequency of a given genotype.
- Answer: E. Genotypic frequency

12. The frequency of physical attributes being observed.
- Answer: J. Phenotypic frequency

13. Traits with phenotypes influenced by two or more genes.
- Answer: F. Polygenic traits

---

Determine the Genotypic Frequencies

#### Punnett Square for \( H \) and \( h \):
```
H h
H HH Hh
H HH Hh
```
- HH: 2 squares (out of 4 total)
- Hh: 2 squares (out of 4 total)
- hh: 0 squares (out of 4 total)

Genotypic frequencies:
- HH: \( \frac{2}{4} = 0.5 \) or 50%
- Hh: \( \frac{2}{4} = 0.5 \) or 50%
- hh: \( \frac{0}{4} = 0 \) or 0%

#### Punnett Square for \( A \) and \( a \):
```
A a
A AA Aa
a Aa aa
```
- AA: 1 square (out of 4 total)
- Aa: 2 squares (out of 4 total)
- aa: 1 square (out of 4 total)

Genotypic frequencies:
- AA: \( \frac{1}{4} = 0.25 \) or 25%
- Aa: \( \frac{2}{4} = 0.5 \) or 50%
- aa: \( \frac{1}{4} = 0.25 \) or 25%

#### Punnett Square for \( B \) and \( b \):
```
B b
B BB Bb
b Bb bb
```
- BB: 1 square (out of 4 total)
- Bb: 2 squares (out of 4 total)
- bb: 1 square (out of 4 total)

Genotypic frequencies:
- BB: \( \frac{1}{4} = 0.25 \) or 25%
- Bb: \( \frac{2}{4} = 0.5 \) or 50%
- bb: \( \frac{1}{4} = 0.25 \) or 25%

---

Determine the Genotypic Frequencies for Dihybrid Cross

The Punnett square for a dihybrid cross involving two genes (\( Y \) and \( R \)) is already provided:

```
YR Yr yR yr
YR YYRR YYRr YyRR YyRr
Yr YYRr YYrr YyRr Yyrr
yR YyRR YyRr yyRR yyRr
yr YyRr Yyrr yyRr yyrr
```

#### Counting Each Genotype:
- YYRR: 1 square
- YYRr: 2 squares
- YYrr: 1 square
- YyRR: 2 squares
- YyRr: 4 squares
- Yyrr: 2 squares
- yyRR: 1 square
- yyRr: 2 squares
- yyrr: 1 square

#### Genotypic Frequencies:
- YYRR: \( \frac{1}{16} = 0.0625 \) or 6.25%
- YYRr: \( \frac{2}{16} = 0.125 \) or 12.5%
- YYrr: \( \frac{1}{16} = 0.0625 \) or 6.25%
- YyRR: \( \frac{2}{16} = 0.125 \) or 12.5%
- YyRr: \( \frac{4}{16} = 0.25 \) or 25%
- Yyrr: \( \frac{2}{16} = 0.125 \) or 12.5%
- yyRR: \( \frac{1}{16} = 0.0625 \) or 6.25%
- yyRr: \( \frac{2}{16} = 0.125 \) or 12.5%
- yyrr: \( \frac{1}{16} = 0.0625 \) or 6.25%

---

Final Answer Summary

#### Vocabulary:
1. G. Monohybrid cross
2. I. Dihybrid cross
3. L. Punnett square
4. A. Gene
5. M. Trait
6. H. Allele
7. C. Dominant
8. D. Recessive
9. B. Heterozygous
10. K. Homozygous
11. E. Genotypic frequency
12. J. Phenotypic frequency
13. F. Polygenic traits

#### Genotypic Frequencies:
- \( H \) and \( h \):
- HH: 50%
- Hh: 50%
- hh: 0%

- \( A \) and \( a \):
- AA: 25%
- Aa: 50%
- aa: 25%

- \( B \) and \( b \):
- BB: 25%
- Bb: 50%
- bb: 25%

- Dihybrid Cross (\( Y \) and \( R \)):
- YYRR: 6.25%
- YYRr: 12.5%
- YYrr: 6.25%
- YyRR: 12.5%
- YyRr: 25%
- Yyrr: 12.5%
- yyRR: 6.25%
- yyRr: 12.5%
- yyrr: 6.25%

\boxed{\text{See above for detailed explanations and answers.}}