A scientifically rigorous 7th-grade lesson on traits and heredity. Students explore dominant and recessive allele patterns in human and canine specimens, master simplified 2x2 Punnett square genetic forecasting models, and simulate inheritance combinations in a canine genome lab.
Prepare for the Canine Genome Lab. Draw a straight line matching the genetic zygosity term to its correct allelic description (using ear morphology E / e).
Homozygous Dominant
Heterozygous
Homozygous Recessive
Ee (One dominant, one recessive)
ee (Two recessive alleles)
EE (Two dominant alleles)
3 Genetic Concept Synthesis Map
Write a concise, scientific definition of Genotype and Phenotype in your own words, utilizing our structural blueprint/construction analogy to illustrate the difference.
Genotype (The Blueprint):
Phenotype (The Expression):
Submit completed graphic organizer for review. Page 2 of 2
E
E
e
What fraction of offspring will be heterozygous (Ee)?
What is the probability of offspring displaying erect ears?
B Scenario 2: Canine Coat Texture
Cross: Ff × ff
Curly coat (F) is dominant over straight sleek coat (f). Solve the cross for a heterozygous sire (Ff) and a homozygous recessive straight-coated dam (ff).
F
f
f
f
What is the statistical probability of curly-coated offspring?
What fraction of offspring will exhibit straight coats (ff)?
C Scenario 3: Caudal Structure Inheritance
Cross: Tt × Tt
Elongated tails (T) are dominant over naturally truncated bobtails (t). Solve the cross for two heterozygous parents (Tt × Tt).
T
t
T
t
What is the percentage of homozygous recessive (tt) offspring?
How many predicted offspring out of 4 will display elongated tails?
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GENERATION III
III-1
Straight (ff)
III-2
Curly
Hereditary Outcome Analysis
Observe individual I-2 on the pedigree. Explain how her physical phenotype (straight coat) dictates her exact genotype. Based on the laws of dominance, why is she considered homozygous recessive rather than heterozygous?
Assess the mating of II-3 and II-4. Since both express curly coats but produced a straight-coated offspring (III-1), explain why both parents must carry a hidden recessive allele. Use a Punnett square to predict the percent probability of their next offspring having a straight coat.
Analyze your custom specimen from the coin-flip trial on Page 1. Identify which of the six traits resulted in a heterozygous configuration. Select one of these traits and calculate the expected genotypic and phenotypic ratios if your specimen were crossed with another heterozygous specimen.
Pedigree Analysis standards mapped directly to MS-LS3-2 genetic modeling curriculum. Page 2 of 2
• Homozygous Rec: ee (Two recessive alleles)
• Genotype vs Phenotype: Genotype is the symbolic allele code (blueprint); Phenotype is the physical expression (the actual construction).
Student must state that since straight coat is a recessive phenotype, individual I-2 must possess a homozygous recessive genotype (ff). Under Mendelian inheritance, the presence of even a single dominant allele (F) would trigger functional curly coat protein synthesis, completely masking the recessive phenotype.
For parent II-3 and II-4 (both curly-coated) to produce a straight-coated offspring (III-1: ff), both parents must possess a copy of the recessive f allele to pass down. Thus, both are heterozygous (Ff). Solve via a 2x2 grid (Ff × Ff): yields 1 FF, 2 Ff, 1 ff. The statistical probability of a straight-coated offspring is exactly 25% (or 1/4).
Question 3 Solution: Trial Assortment Ratio Calculations
Verify they listed their specific heterozygous traits from Page 1 (e.g. Ff, Ee, Tt, Ss, Pp, or Bb). Crossing two heterozygotes for any Mendelian trait (e.g. Ff × Ff) always yields identical predicted progeny ratios:
• Expected Genotypic Ratio: 1 Homozygous Dominant : 2 Heterozygous : 1 Homozygous Recessive (or 1:2:1 ratio).
• Expected Phenotypic Ratio: 3 Dominant Expressed : 1 Recessive Expressed (or 3:1 ratio).
Genomic Data Verification Check: For Page 1 of the lab, ensure the student filled in every registry row. Flip 1 and Flip 2 must be combined logically (e.g., Flip 1 is "H", Flip 2 is "T" = Genotype is "Ff", Phenotype is "Curly").
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Ee
Ee
What fraction of offspring will be heterozygous (Ee)?
2/4 (or 1/2)
What is the probability of offspring displaying erect ears (ee)?
0% (All are EE/Ee)
B Scenario 2: Canine Coat Texture (Ff × ff)
Solved Grid & Prompts
F
f
f
Ff
ff
f
Ff
ff
What is the statistical probability of curly-coated offspring?
50% (Ff)
What fraction of offspring will exhibit straight coats (ff)?
2/4 (or 1/2)
C Scenario 3: Caudal Structure Inheritance (Tt × Tt)
Solved Grid & Prompts
T
t
T
TT
Tt
t
Tt
tt
What is the percentage of homozygous recessive (tt) offspring?
25% (tt)
How many predicted offspring out of 4 will display elongated tails?
3 out of 4 (TT, Tt)
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