Class 10 Biology - Heredity and Evolution

Activities

Activity 8.1: Inheritance of Earlobe Types

Aim/Objective: To observe and analyze the inheritance pattern of free and attached earlobes in a human population (classroom).

Materials Required:

• Survey data from classmates and their parents
• Notebook and pen

Procedure:

1. Observe the earlobes of all students in the class and categorize them as "Free" or "Attached."
2. Calculate the percentage of students with each type of earlobe.
3. Collect data regarding the earlobe types of the parents of each student.
4. Correlate the student's earlobe type with that of their parents (e.g., if both parents have attached lobes, what does the student have?).
5. Identify which trait appears more frequently and how it is passed down.

Observation:

• Most students have free earlobes, while a smaller number have attached earlobes.
• In many cases, if at least one parent has free earlobes, the child also has free earlobes. If both parents have attached earlobes, the child almost always has attached earlobes.

Explanation:

• Earlobe type is a genetic trait controlled by a single gene. The "Free Earlobe" trait is dominant (represented as 'E'), and the "Attached Earlobe" trait is recessive (represented as 'e').
• A person with a dominant allele (EE or Ee) will have free earlobes. A person only expresses the attached earlobe trait if they inherit two recessive alleles (ee), one from each parent.
• This follows Mendelian inheritance rules where the dominant trait masks the expression of the recessive trait in a heterozygous individual.

Conclusion:

• Earlobe attachment is an inherited trait, where free earlobes are generally dominant over attached earlobes.

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Activity 8.2: Confirming Mendelian Ratios (F2 Generation)

Aim/Objective: To design an experiment/analysis to confirm the 1:2:1 genotypic ratio in the F2 generation of a monohybrid cross.

Materials Required:

• Mendelian cross data (Tall vs. Short pea plants)
• Punnett square diagrams

Procedure:

1. Consider the F1 generation of a cross between a pure tall (TT) and a pure short (tt) pea plant, where all offspring are heterozygous tall (Tt).
2. Perform self-pollination of these F1 (Tt) plants.
3. Observe the physical characteristics (phenotype) of the F2 offspring.
4. To confirm the genotypic ratio (TT:Tt:tt), perform a "test cross" by breeding F2 tall plants with a pure recessive short plant (tt).
5. Analyze the offspring of the test cross to determine the genotype of the F2 tall parent.

Observation:

• The F2 generation shows a phenotypic ratio of 3 tall : 1 short.
• Through further breeding (test crosses), it is revealed that among the tall plants, one-third are pure breeding (TT) and two-thirds are hybrid (Tt).

Explanation:

• According to Mendel's Law of Segregation, alleles separate during gamete formation and recombine randomly during fertilization.
• In a monohybrid cross (Tt x Tt), the possible combinations are TT, Tt, tT, and tt. This results in a genotypic ratio of 1 (TT) : 2 (Tt) : 1 (tt).
• Since 'T' is dominant, both TT and Tt appear tall, leading to the 3:1 phenotypic ratio observed by Mendel.

Conclusion:

• The inheritance of a single trait follows a specific mathematical ratio (1:2:1 genotype, 3:1 phenotype) in the second generation, proving the discrete nature of genetic factors.