📄 7th Grade Life Science: Genetics and Punnett Squares Worksheet
📌 1. True / False
1. Genes are segments of DNA that determine an organism's traits.
2. A dominant allele is only expressed when two copies are present.
3. Punnett squares show the actual offspring of a genetic cross, not just probabilities.
4. Alleles are different forms of the same gene.
5. An organism with two identical alleles for a trait is called heterozygous.
✏️ 2. Fill in the Blanks
1. The study of how traits are passed from parents to offspring is called .
2. A square is a diagram used to predict the possible genotypes of offspring from a genetic cross.
3. An organism's genetic makeup, represented by its alleles, is known as its .
4. The observable physical characteristics or traits of an organism are referred to as its .
5. When an organism has two different alleles for a particular trait, it is described as .
🔗 3. Matching
« A different form or version of a gene.
« Having two identical alleles for a particular gene (e.g., AA or aa).
« Having two different alleles for a particular gene (e.g., Aa).
« An allele that is always expressed when it is present.
« An allele that is only expressed when two copies are present, and no dominant allele is present.
✍️ 4. Short Answer Questions
1. What is the main purpose of using a Punnett square?
💡 Suggested Answer: The primary purpose of a Punnett square is to predict the probability of offspring inheriting specific genotypes and phenotypes from their parents in a genetic cross.
2. Explain the difference between a genotype and a phenotype, providing an example for each.
💡 Suggested Answer: Genotype refers to an organism's genetic makeup, represented by the combination of alleles (e.g., TT, Tt, tt for height). Phenotype refers to the observable physical characteristics or traits that result from the genotype (e.g., tall or short height).
🎯 5. Multiple Choice
1. Which term describes an allele that is only expressed when two copies are present?
2. If an organism has the genotype Rr for a trait, what does this indicate?
3. A Punnett square typically shows the possible genetic outcomes for offspring from a cross between how many parents?
📝 6. Open-Ended Questions
1. In pea plants, tall (T) is dominant over short (t). If a homozygous dominant tall plant is crossed with a homozygous recessive short plant, what are the genotypes and phenotypes of the F1 generation? Show your work using a Punnett square.
💡 Solution Steps:
1. Identify the parents' genotypes:
Homozygous dominant tall plant: TT
Homozygous recessive short plant: tt
2. Determine the gametes each parent can produce:
TT parent produces only T gametes.
tt parent produces only t gametes.
3. Construct a Punnett square:
\[
\begin{array}{|c|c|c|}
& \text{T} & \text{T} \\
\text{t} & \text{Tt} & \text{Tt} \\
\text{t} & \text{Tt} & \text{Tt} \\
\end{array}
\]
4. Determine the genotypes and phenotypes of the F1 generation:
Genotypes: All offspring will have the genotype Tt (100% heterozygous).
Phenotypes: All offspring will be tall (100% tall), because the T allele is dominant.
2. In guinea pigs, black fur (B) is dominant over white fur (b). Cross two heterozygous guinea pigs (Bb x Bb) and determine the genotypic and phenotypic ratios of their offspring. Show your work.
💡 Solution Steps:
1. Identify the parents' genotypes:
Both parents are heterozygous black: Bb
2. Determine the gametes each parent can produce:
Each Bb parent can produce B gametes and b gametes.
3. Construct a Punnett square:
\[
\begin{array}{|c|c|c|}
& \text{B} & \text{b} \\
\text{B} & \text{BB} & \text{Bb} \\
\text{b} & \text{Bb} & \text{bb} \\
\end{array}
\]
4. Determine the genotypic and phenotypic ratios:
Genotypes:
BB: 1 out of 4 (25%)
Bb: 2 out of 4 (50%)
bb: 1 out of 4 (25%)
Genotypic Ratio: 1 BB : 2 Bb : 1 bb
Phenotypes:
Black fur (BB and Bb): 3 out of 4 (75%)
White fur (bb): 1 out of 4 (25%)
Phenotypic Ratio: 3 Black : 1 White
3. A scientist crosses a purebred red flower (RR) with a purebred white flower (rr). Red is dominant over white. What percentage of the offspring will have red flowers? Show your work using a Punnett square.
💡 Solution Steps:
1. Identify the parents' genotypes:
Purebred red flower: RR
Purebred white flower: rr
2. Determine the gametes each parent can produce:
RR parent produces only R gametes.
rr parent produces only r gametes.
3. Construct a Punnett square:
\[
\begin{array}{|c|c|c|}
& \text{R} & \text{R} \\
\text{r} & \text{Rr} & \text{Rr} \\
\text{r} & \text{Rr} & \text{Rr} \\
\end{array}
\]
4. Determine the percentage of offspring with red flowers:
All offspring (100%) will have the genotype Rr. Since red (R) is dominant over white (r), all Rr offspring will express the red phenotype.
Therefore, 100% of the offspring will have red flowers.
Name Surname: .................................. Date: .... / .... / 202...
Genetics and Punnett Squares Worksheet
SCORE
A. True (T) / False (F)
( .... )
Genes are segments of DNA that determine an organism's traits.
( .... )
A dominant allele is only expressed when two copies are present.
( .... )
Punnett squares show the actual offspring of a genetic cross, not just probabilities.
( .... )
Alleles are different forms of the same gene.
( .... )
An organism with two identical alleles for a trait is called heterozygous.
B. Fill in the Blanks
1)
The study of how traits are passed from parents to offspring is called .....................
2)
A .................... square is a diagram used to predict the possible genotypes of offspring from a genetic cross.
3)
An organism's genetic makeup, represented by its alleles, is known as its .....................
4)
The observable physical characteristics or traits of an organism are referred to as its .....................
5)
When an organism has two different alleles for a particular trait, it is described as .....................
C. Matching Concepts
( .... )
A different form or version of a gene.
- Homozygous
( .... )
Having two identical alleles for a particular gene (e.g., AA or aa).
- Recessive Allele
( .... )
Having two different alleles for a particular gene (e.g., Aa).
- Heterozygous
( .... )
An allele that is always expressed when it is present.
- Dominant Allele
( .... )
An allele that is only expressed when two copies are present, and no dominant allele is present.
- Allele
D. Short Answer Questions
1)
What is the main purpose of using a Punnett square?
2)
Explain the difference between a genotype and a phenotype, providing an example for each.
E. Multiple Choice Questions
1)
Which term describes an allele that is only expressed when two copies are present?
A) DominantB) RecessiveC) HomozygousD) Heterozygous
2)
If an organism has the genotype Rr for a trait, what does this indicate?
A) It is homozygous dominant.B) It is homozygous recessive.C) It is heterozygous.D) It will always express the recessive phenotype.
3)
A Punnett square typically shows the possible genetic outcomes for offspring from a cross between how many parents?
A) OneB) TwoC) ThreeD) Four
F. Open-Ended Questions
1)
In pea plants, tall (T) is dominant over short (t). If a homozygous dominant tall plant is crossed with a homozygous recessive short plant, what are the genotypes and phenotypes of the F1 generation? Show your work using a Punnett square.
2)
In guinea pigs, black fur (B) is dominant over white fur (b). Cross two heterozygous guinea pigs (Bb x Bb) and determine the genotypic and phenotypic ratios of their offspring. Show your work.
3)
A scientist crosses a purebred red flower (RR) with a purebred white flower (rr). Red is dominant over white. What percentage of the offspring will have red flowers? Show your work using a Punnett square.