AP Biology Chapter 14,15 Textbook-12e

Chapter 14: Mendel and the Gene Idea

14.1 Mendel's Experimental Approach

Gregor Mendel: Monk and naturalist who established principles of heredity using pea plants.

• Characteristics Studied: Flower color (purple vs. white), seed shape, etc.

• Inheritance Theory: Developed through quantitative analysis of offspring ratios from specific crosses.

• Key Concepts:

  • Law of Segregation: Two alleles for each character segregate during gamete formation.

  • Genotypic Ratio: Mendel found a 3:1 ratio in F2 generation for dominant vs. recessive traits.

14.2 Genetics and Probability

Probability Laws: Genetics problems can be solved using probability rules (similar to games of chance).

• Example: Predicting offspring ratios using Punnett squares.

• Genetic Crosses:

  • Monohybrid Crosses: One trait. Predicts 3:1 ratio in F2.

  • Dihybrid Crosses: Two traits. Predicts 9:3:3:1 ratio in F2.

14.3 Complex Inheritance Patterns

Beyond Mendelian Genetics: Many traits do not follow simple dominant/recessive patterns.

• Polygenic Inheritance: Traits controlled by multiple genes (e.g., skin color, height).

• Pleiotropy: One gene affecting multiple traits (e.g., sickle-cell disease).

• Epistasis: One gene affects the expression of another.

14.4 Human Traits and Pedigree Analysis

Mendelian Patterns in Humans: Some human traits follow Mendelian inheritance (e.g., albinism, cystic fibrosis).

• Pedigrees: Used to trace inheritance of traits in families.

• Calculating Risks: Predicting genotype probabilities based on family history (e.g., cystic fibrosis risk).

Key Concepts Summary

• Independent Assortment: Genes on different chromosomes assort independently during gamete formation.

• Testcross: Cross between an individual with unknown genotype and a homozygous recessive individual to determine genotype of the former.

• Plant Examples: Mendel used true-breeding plants to analyze traits orderly to see ratios of traits.

Phenotypic Ratios

• Monohybrid Cross - 3:1 ratio (F2 generation).

• Dihybrid Cross - 9:3:3:1 ratio (F2 generation).

• Testcross Outcome: Helps determine unknown genotype based observed offspring phenotypes.

Genetic Terminology

• Genotype: The genetic makeup (PP, Pp, pp).

• Phenotype: Observable trait (purple or white flowers).

• Homozygous: Organism with identical alleles.

• Heterozygous: Organism with different alleles.

Chapter 15: The Chromosomal Basis of Inheritance

15.1 Chromosomes and Inheritance

Chromosomes: Structures made of DNA and proteins that contain genes.

• Chromosomal Theory of Inheritance: Genes are located on chromosomes and segregate during meiosis.

15.2 Sex-Linked Genes

Sex Chromosomes: X and Y chromosomes determine sex in many organisms.

• X-Linked Traits: Traits carried on the X chromosome; often affect males more as they have only one X.

15.3 Genetic Linkage

Linkage: When genes are located close together on the same chromosome, they tend to be inherited together.

• Recombination Frequency: Calculated to determine how far apart genes are on a chromosome, often expressed in units of map distance.

15.4 Changes in Chromosome Number

Aneuploidy: Abnormal number of chromosomes due to nondisjunction during meiosis.

• Examples: Down syndrome (trisomy 21), Turner syndrome (monosomy X).

15.5 Chromosomal Mutations

Mutations: Changes in chromosome structure can lead to gene duplications, deletions, inversions, and translocations.

• These mutations can impact an organism's phenotype and can cause genetic disorders.

Key Terms

• Gene: A segment of DNA that encodes for a protein.

• Allele: Different forms of a gene.

• Phenotype: Observable characteristics resulting from genotype.

• Genotype: Specific allele combinations an organism carries.

• Karyotype: A display of the complete set of chromosomes in an organism.

• Nondisjunction: Failure of homologous chromosomes to separate properly during cell division.