Grade 9 Science DLL: Mendelian Genetics and Heredity
Mendelian Genetics and Heredity
Learning Standards
Content Standard
Learners demonstrate understanding of the basic concepts of genetics including Mendelian inheritance
Performance Standard
Learners shall be able to predict phenotypes and genotypes of offspring using Punnett squares
Learning Competency
Understanding Gregor Mendel's principles of inheritance and basic genetics
Code: S9LT-IIIi-32
Complete Lesson Plan
Learning Objectives
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Explain Mendel's laws of inheritance
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Differentiate between genotype and phenotype
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Use Punnett squares to predict offspring traits
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Understand dominant and recessive alleles
Lesson Procedures
motivation
Activity: Family Trait Survey (5 minutes)
Ask students to identify traits they share with their parents:
- Can you roll your tongue?
- Do you have dimples?
- Is your earlobe attached or free?
- What is your hair texture?
Discuss: Why do we resemble our parents? How are traits passed down?
This introduces the concept of heredity.
presentation
Gregor Mendel and the Principles of Heredity (17 minutes)
Who was Gregor Mendel?
- Austrian monk who studied pea plants (1860s)
- Father of modern genetics
Key Terms:
- Gene: Unit of heredity
- Allele: Different forms of a gene (e.g., T or t)
- Dominant allele: Expressed when present (capital letter: T)
- Recessive allele: Only expressed when homozygous (lowercase: t)
- Genotype: Genetic makeup (TT, Tt, tt)
- Phenotype: Physical appearance (tall or short)
- Homozygous: Two identical alleles (TT or tt)
- Heterozygous: Two different alleles (Tt)
Mendel's Law of Segregation: Allele pairs separate during gamete formation, and randomly unite at fertilization
Using Punnett Squares: Demonstrate a monohybrid cross:
- Parent 1: Tt (heterozygous tall)
- Parent 2: Tt (heterozygous tall)
- Offspring: 1 TT : 2 Tt : 1 tt (3:1 phenotype ratio)
Draw and explain step-by-step on the board.
generalization
Summary and Applications (5 minutes)
- Mendel discovered the basic principles of heredity through pea plant experiments
- Traits are inherited through genes, which have different forms called alleles
- Dominant alleles mask recessive alleles
- Punnett squares help predict offspring traits
- These principles explain why offspring resemble parents but aren't identical (except identical twins)
- Modern genetics builds on Mendel's work to understand genetic diseases, breeding, and evolution
guided practice
Activity: Completing Punnett Squares (12 minutes)
Provide practice problems:
- Cross between homozygous tall (TT) and short (tt) pea plant
- Cross between two heterozygous purple flowers (Pp)
Students complete Punnett squares and determine:
- Genotypic ratios
- Phenotypic ratios
- Percentage of each trait
Circulate and provide guidance.
independent practice
Problem-Solving Activity (8 minutes)
Students solve independently:
In guinea pigs, black fur (B) is dominant over white fur (b). Cross a heterozygous black guinea pig with a white guinea pig.
Determine:
- Parent genotypes
- Possible offspring genotypes
- Phenotypic ratio
- Probability of black vs. white offspring
preliminary activities
Prayer and Greetings (2 minutes)
Attendance Check (1 minute)
Review of Previous Lesson (3 minutes) Recall DNA structure and the role of genes in heredity.
Assessment
answers
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Genotype is the genetic makeup (combination of alleles), while phenotype is the observable physical characteristic or trait expressed
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Tall - because T (tall) is dominant and is expressed even when paired with t (recessive)
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25% (only tt genotypes show the recessive phenotype, which is 1 out of 4 offspring)
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Allele pairs separate during the formation of gametes (sex cells), so each gamete carries only one allele for each gene. These alleles then randomly combine during fertilization
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All offspring will be Yy (100% heterozygous), showing the dominant yellow seed phenotype
questions
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What is the difference between genotype and phenotype?
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If T (tall) is dominant over t (short), what would be the phenotype of a plant with genotype Tt?
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In a cross between Aa × Aa, what percentage of offspring will have the recessive phenotype?
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What is Mendel's Law of Segregation?
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In pea plants, yellow seeds (Y) are dominant over green seeds (y). If you cross YY × yy, what will be the genotype of all F1 offspring?
Materials & Resources
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Punnett square worksheets
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Colored markers
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Trait cards showing dominant/recessive traits
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Coin for demonstrating probability
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Whiteboard and markers
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Visual aids of pea plant traits
remarks
Students showed strong interest in applying genetics to human traits. Visual representation through Punnett squares was effective. Some students initially confused genotype and phenotype but improved with practice.
assignment
Homework Assignment:
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In humans, the ability to roll your tongue is dominant (R) over the inability to roll (r). If both parents are heterozygous tongue rollers (Rr), create a Punnett square and determine:
- Genotypic ratio
- Phenotypic ratio
- Probability their child can roll their tongue
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Research and list 3 human traits that follow Mendelian inheritance patterns
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Explain in your own words why understanding genetics is important in medicine and agriculture
Write your answers in your science notebook.
subject matter
Topic: Mendelian Genetics and Heredity
Key Concepts:
- Genes and alleles
- Dominant and recessive traits
- Genotype vs. phenotype
- Law of Segregation
- Law of Independent Assortment
- Punnett square analysis
Reference Materials:
Science 9 Learner's Material, pp. 234-256
Materials Needed:
Punnett square templates, coin for probability demonstration, trait cards