Chapter 12 and 13 Answer Key

Section 1: Historical Experiments and Principles

1. Josef Kolreuter: Used tobacco plants in experiments. Observed that hybrids had intermediate traits compared to their parents.

T.A. Knight: Conducted experiments on garden peas. Demonstrated the concept of self-fertilization and cross-fertilization.

Gregor Mendel: Used pea plants and established the principles of segregation and independent assortment.

Sutton and Boveri: Studied meiosis and linked chromosome behavior to Mendel's principles.

2. Mendel's Principle of Segregation: Each individual has two alleles for each gene, one inherited from each parent, and these alleles segregate during gamete formation.

Mendel's Principle of Independent Assortment: Alleles of different genes assort independently during gamete formation.

Section 2: Theories of Inheritance

3.

- Blending Inheritance: Suggested that offspring's traits are a blend of the parental traits.

- Inheritance of Acquired Characteristics: Proposed that acquired traits could be inherited.

- Theory of Particulate Inheritance: Proposed that traits are determined by discrete, inheritable factors (genes).

- Chromosome Theory of Inheritance: Linked the behavior of chromosomes to Mendel's principles, showing how genes are located on chromosomes.

Section 3: Punnett Squares and Crosses

4.

a. Monohybrid Cross: Use Punnett square to show alleles for a single trait. Example: Tt x tt. Expected ratio: 1:1 (Tt: tt) genotypically, all will have the dominant trait phenotypically.

b. Dihybrid Cross: Use Punnett square to show alleles for two different traits. Example: RrYy x RrYy. Expected ratio: 9:3:3:1 (RRYY: RrYY: RRyy: Rryy) genotypically, 9:3:3:1 phenotypically.

5. Phenotypic and genotypic ratios should match the expected outcomes for each cross.

6. A test cross is used to determine the genotype of an individual with a dominant phenotype. It involves crossing the individual with a homozygous recessive individual.

Section 4: Determining Genotypes and Phenotypes

7. By analyzing the F1 and F2 generations, you can deduce the possible genotypes and phenotypes of the parents.

8. Different inheritance patterns can be identified based on the provided ratios, such as Mendelian inheritance, codominance, incomplete dominance, or sex-linked inheritance.

Section 5: Complex Inheritance Patterns

9. Incomplete Dominance: Offspring's phenotype is a blend of the parents' phenotypes.

Codominance: Offspring express both parental phenotypes simultaneously.

Sex-Linked Traits: Traits determined by genes located on the sex chromosomes.

Section 6: Advanced Genetic Concepts

10.

a. Pleiotropy: A single gene influences multiple, seemingly unrelated traits.

b. Multiple Allelism: A gene has more than two alleles.

c. Epistasis: One gene's allele affects the expression of another gene's allele.

d. Polygenic Inheritance: Multiple genes contribute to a single trait.

e. Environmental Effects: Environmental factors influence gene expression.

f. Linkage Mapping: Mapping the relative positions of genes on a chromosome.

11. Discrete traits have distinct categories (e.g., Mendelian traits), while quantitative traits show a range of variation (e.g., height, weight).

Section 7: Pedigree Analysis

12. Interpret the given pedigree diagram, considering patterns of inheritance, genotypes, and phenotypes based on symbols and relationships within the pedigree.

Section 8: Bonus Question

13. Provide an example of a real-life genetic disorder or trait and describe its inheritance pattern and the underlying genetic mechanisms.

Feel free to ask if you need more information or explanations for any of the answers!