Asked by ggg
write a simple lab report on mouse genetics.
What is the effect of the genes of the parental mice on the fur color of the offspring mice?
If either parent mouse passes a dominant allele, the offspring will have black fur.
Independent Variable: genotype of parents
Dependent Variable: traits of offspring
Note: The variables will switch their roles (independent vs. dependent) in steps 4 and 5.
Lab Procedure
In each of steps 1 through 3 on the next page, you will cross a different female and male pair of
mice and examine the inheritance of fur color. Repeat the substeps below each time.
a)
b)
c)
d)
e)
f)
In the Punnett square, fill in the shaded boxes with the alleles of each parent. Use B for the dominant
allele (black fur) and b for the recessive allele (white fur).
Fill in the unshaded boxes of the Punnett square with all possible offspring genotypes.
Based on the genotypes, fill in the table to the right with the predicted percentage (0%, 25%, 50%,
75%, or 100%) of offspring for each phenotype, black or white fur.
Confirm your prediction by simulating ten offspring. You can simulate breeding using technology
In the data table, record the number (out of 10) and percentage (out of 100%) of each phenotype in
the rows “Simulated Number” and “Simulated Percentages.”
In the box labeled “Comparison Statement,” write a comparison of the predictions of the Punnett
square with the offspring you saw.
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Title: Inheritance of Fur Color in Mice (Simple Genetics Lab)
Purpose
To determine how the genotypes of parental mice affect the fur color of their offspring when black (B) is dominant to white (b).
Hypothesis
If either parent contributes a dominant B allele, then offspring will have black fur. Therefore crosses that produce any B alleles will produce black offspring, and only bb offspring will be white.
Variables
- Independent variable: genotype of the parents (parental alleles).
- Dependent variable: phenotype of the offspring (black or white fur).
Note: In later steps of the full lab (steps 4 and 5) these roles can be reversed conceptually (for example, selecting parents by offspring phenotype and observing resulting parental genotype distributions), but for steps 1–3 the genotype of the parents is the independent variable.
Materials
- Punnett squares (paper or software)
- Calculator or spreadsheet
- Random-number generator or simulation software (to simulate 10 offspring per cross)
- Pen/pencil
Procedure (repeat for each of three different parental pairs)
a) Choose a female and a male and record their genotypes.
b) Draw a 2×2 Punnett square.
c) Label the shaded boxes with each parent’s alleles (one parent’s allele(s) across the top, the other down the side).
d) Fill the four unshaded boxes with all possible offspring genotypes.
e) From the genotypes, predict phenotype percentages for black and white fur (0%, 25%, 50%, 75% or 100%).
f) Simulate breeding to produce 10 offspring and record the number and percentage of each phenotype. Write a comparison statement between the Punnett prediction and the simulated results.
Cross 1
Parents: Female BB × Male BB
c) Parent alleles: Female: B, B ; Male: B, B
d) Punnett square offspring genotypes:
- All four boxes: BB
Predicted phenotype percentages:
- Black = 100% (BB)
- White = 0%
Simulated (10 offspring): 10 black, 0 white → 100% black, 0% white
Comparison statement: Simulation matches prediction exactly (all offspring black), as expected for BB × BB.
Cross 2
Parents: Female BB × Male bb
c) Parent alleles: Female: B, B ; Male: b, b
d) Punnett square offspring genotypes:
- All four boxes: Bb
Predicted phenotype percentages:
- Black = 100% (Bb are black because B is dominant)
- White = 0%
Simulated (10 offspring): 10 black, 0 white → 100% black, 0% white
Comparison statement: Simulation matches prediction exactly (all offspring black), as expected for BB × bb.
Cross 3
Parents: Female Bb × Male Bb
c) Parent alleles: Female: B, b ; Male: B, b
d) Punnett square offspring genotypes:
- Top-left: BB
- Top-right: Bb
- Bottom-left: Bb
- Bottom-right: bb
Predicted genotype percentages: 25% BB, 50% Bb, 25% bb
Predicted phenotype percentages:
- Black = 75% (BB + Bb)
- White = 25% (bb)
Simulated (10 offspring): example result — 8 black, 2 white → 80% black, 20% white
Comparison statement: The simulation is close to the Punnett-square prediction (75% black / 25% white). Small-sample sampling variation caused the difference (10 offspring is a small sample).
Summary data table (condensed)
- Cross 1 (BB × BB): Predicted 100% black; Simulated 10/10 black (100%).
- Cross 2 (BB × bb): Predicted 100% black; Simulated 10/10 black (100%).
- Cross 3 (Bb × Bb): Predicted 75% black, 25% white; Simulated 8/10 black (80%), 2/10 white (20%).
Analysis and Conclusion
- The results support the hypothesis: presence of at least one B allele produces black fur in offspring.
- Punnett squares correctly predict expected genotype and phenotype frequencies for these simple Mendelian crosses.
- Deviations between predicted percentages and simulated results are expected with small sample sizes (sampling error). Larger sample sizes would tend to match predictions more closely.
Sources of Error / Limitations
- Small simulation sample (10 offspring) gives sampling noise; real experiments should use larger numbers.
- The model assumes complete dominance of B over b and no other genes affecting fur color.
- Real biological factors (reduced viability of certain genotypes, linkage, mutation, or environment) are not included.
Extension / Note about steps 4 and 5
- If the roles of variables are switched (offspring phenotype used as the criterion for selecting parents), the experimental design changes: you would select parents based on offspring traits and then measure resulting genotypes or subsequent offspring traits. This is a useful way to explore selection and how phenotype-based mating can alter genotype frequencies over generations.
Comparison statement (general)
- For deterministic crosses (BB × BB and BB × bb), the observed offspring exactly matched Punnett-square predictions. For the heterozygote cross (Bb × Bb), the simulated offspring closely approximated the predicted 75% black / 25% white but differed due to small sample size; this demonstrates both the predictive power of Punnett squares and the role of chance in small samples.
End of report.
Purpose
To determine how the genotypes of parental mice affect the fur color of their offspring when black (B) is dominant to white (b).
Hypothesis
If either parent contributes a dominant B allele, then offspring will have black fur. Therefore crosses that produce any B alleles will produce black offspring, and only bb offspring will be white.
Variables
- Independent variable: genotype of the parents (parental alleles).
- Dependent variable: phenotype of the offspring (black or white fur).
Note: In later steps of the full lab (steps 4 and 5) these roles can be reversed conceptually (for example, selecting parents by offspring phenotype and observing resulting parental genotype distributions), but for steps 1–3 the genotype of the parents is the independent variable.
Materials
- Punnett squares (paper or software)
- Calculator or spreadsheet
- Random-number generator or simulation software (to simulate 10 offspring per cross)
- Pen/pencil
Procedure (repeat for each of three different parental pairs)
a) Choose a female and a male and record their genotypes.
b) Draw a 2×2 Punnett square.
c) Label the shaded boxes with each parent’s alleles (one parent’s allele(s) across the top, the other down the side).
d) Fill the four unshaded boxes with all possible offspring genotypes.
e) From the genotypes, predict phenotype percentages for black and white fur (0%, 25%, 50%, 75% or 100%).
f) Simulate breeding to produce 10 offspring and record the number and percentage of each phenotype. Write a comparison statement between the Punnett prediction and the simulated results.
Cross 1
Parents: Female BB × Male BB
c) Parent alleles: Female: B, B ; Male: B, B
d) Punnett square offspring genotypes:
- All four boxes: BB
Predicted phenotype percentages:
- Black = 100% (BB)
- White = 0%
Simulated (10 offspring): 10 black, 0 white → 100% black, 0% white
Comparison statement: Simulation matches prediction exactly (all offspring black), as expected for BB × BB.
Cross 2
Parents: Female BB × Male bb
c) Parent alleles: Female: B, B ; Male: b, b
d) Punnett square offspring genotypes:
- All four boxes: Bb
Predicted phenotype percentages:
- Black = 100% (Bb are black because B is dominant)
- White = 0%
Simulated (10 offspring): 10 black, 0 white → 100% black, 0% white
Comparison statement: Simulation matches prediction exactly (all offspring black), as expected for BB × bb.
Cross 3
Parents: Female Bb × Male Bb
c) Parent alleles: Female: B, b ; Male: B, b
d) Punnett square offspring genotypes:
- Top-left: BB
- Top-right: Bb
- Bottom-left: Bb
- Bottom-right: bb
Predicted genotype percentages: 25% BB, 50% Bb, 25% bb
Predicted phenotype percentages:
- Black = 75% (BB + Bb)
- White = 25% (bb)
Simulated (10 offspring): example result — 8 black, 2 white → 80% black, 20% white
Comparison statement: The simulation is close to the Punnett-square prediction (75% black / 25% white). Small-sample sampling variation caused the difference (10 offspring is a small sample).
Summary data table (condensed)
- Cross 1 (BB × BB): Predicted 100% black; Simulated 10/10 black (100%).
- Cross 2 (BB × bb): Predicted 100% black; Simulated 10/10 black (100%).
- Cross 3 (Bb × Bb): Predicted 75% black, 25% white; Simulated 8/10 black (80%), 2/10 white (20%).
Analysis and Conclusion
- The results support the hypothesis: presence of at least one B allele produces black fur in offspring.
- Punnett squares correctly predict expected genotype and phenotype frequencies for these simple Mendelian crosses.
- Deviations between predicted percentages and simulated results are expected with small sample sizes (sampling error). Larger sample sizes would tend to match predictions more closely.
Sources of Error / Limitations
- Small simulation sample (10 offspring) gives sampling noise; real experiments should use larger numbers.
- The model assumes complete dominance of B over b and no other genes affecting fur color.
- Real biological factors (reduced viability of certain genotypes, linkage, mutation, or environment) are not included.
Extension / Note about steps 4 and 5
- If the roles of variables are switched (offspring phenotype used as the criterion for selecting parents), the experimental design changes: you would select parents based on offspring traits and then measure resulting genotypes or subsequent offspring traits. This is a useful way to explore selection and how phenotype-based mating can alter genotype frequencies over generations.
Comparison statement (general)
- For deterministic crosses (BB × BB and BB × bb), the observed offspring exactly matched Punnett-square predictions. For the heterozygote cross (Bb × Bb), the simulated offspring closely approximated the predicted 75% black / 25% white but differed due to small sample size; this demonstrates both the predictive power of Punnett squares and the role of chance in small samples.
End of report.
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