P

Week 4

Week 4 Notes – Principles of Heredity & Exam 1 Review

Introduction to Heredity

  • Heredity: Transmission of traits from parents to offspring.

  • Gregor Mendel: Pioneer of genetic inheritance.

  • Traits: Inherited through genes, which are made up of DNA.

Basic Mendelian Genetics

Key Terms:

  • Gene: Segment of DNA coding for a specific protein.

  • Allele: Different forms of a gene (dominant or recessive).

  • Genotype: Genetic makeup of an organism (e.g., AA, Aa, aa).

  • Phenotype: Physical expression of a trait (e.g., brown hair).

  • Homozygous: Two identical alleles for a trait (AA or aa).

  • Heterozygous: Two different alleles for a trait (Aa).

Mendel’s Laws of Inheritance

  1. Law of Segregation:

    • Each parent passes only one allele to offspring.

    • Alleles separate during gamete formation (meiosis).

  2. Law of Independent Assortment:

    • Genes for different traits inherited independently if on different chromosomes.

Dominant vs. Recessive Traits

  • Dominant Allele (A): Expressed even if one copy is present (AA or Aa).

  • Recessive Allele (a): Expressed only when two copies are present (aa).

Punnett Squares

  • Tool to predict genetic inheritance patterns.

  • Example cross: Heterozygous parents (Aa x Aa):

    • 25% AA (homozygous dominant)

    • 50% Aa (heterozygous)

    • 25% aa (homozygous recessive)

Beyond Mendelian Genetics

Complex Inheritance Patterns

  1. Polygenic Traits:

    • Controlled by multiple genes (e.g., skin color, height).

    • Show continuous variation rather than simple dominant/recessive patterns.

  2. Pleiotropy:

    • A single gene affects multiple traits (e.g., Marfan syndrome, sickle cell anemia).

  3. Epigenetics:

    • Environmental factors influence gene expression without changing DNA.

Principles of Heredity & Cell Division

  • Mitosis: Produces two identical diploid cells for growth & repair.

  • Meiosis: Produces four haploid gametes (sperm & egg), increasing genetic diversity.

Chromosomes & Inheritance

  • Humans have 23 pairs (46 total) chromosomes.

  • Autosomes (22 pairs): Carry most genetic traits.

  • Sex chromosomes (1 pair, XX or XY): Determine biological sex.

  • Aneuploidy: Abnormal chromosome number (e.g., Down Syndrome, Trisomy 21).

Key Takeaways from Exam 1 Review

  • Evolution does not always lead to bigger, stronger, faster organisms.

  • Artificial selection differs from natural selection.

  • Amino acids: Building blocks of proteins.

  • Messenger RNA (mRNA): Carries genetic instructions to ribosomes for protein synthesis.

  • Uniformitarianism: Earth's changes are gradual over time (Hutton & Lyell).

  • Mutation: Only source of new alleles in evolution.

  • Adaptive radiation: Darwin’s finches show species diversification in different environments.

  • Mendelian inheritance explains single-gene traits; most traits follow complex inheritance patterns.

Summary of Key Concepts from Week 4

  • Heredity follows Mendelian principles; most traits are complex.

  • Polygenic and pleiotropic inheritance explain traits beyond dominant/recessive patterns.

  • Cell division (mitosis & meiosis) ensures genetic continuity & variation.

  • Chromosomal inheritance and mutations contribute to evolution.

Week 4 Overview Objectives

  • Define key Mendelian terms: dominant/recessive, genotype/phenotype, gene, allele, homozygous/heterozygous.

  • Calculate inheritance of simple dominant/recessive traits using Punnett squares.

  • Understand complex inheritance patterns (polygenic and pleiotropic traits).

Tasks

  1. Review Chapter 3.

  2. Take Exam 1.

Early Ideas about Heredity

  • Historical views of heredity viewed it as mysterious; Pangenesis theory suggested blending of fluids from parents affected offspring.

  • Gregor Mendel: Conducted plant breeding experiments; discovered predictable inheritance patterns not observable via blending theories.

Basic Genetics Terminology

  • Alleles: Forms of genes; traits studied by Mendel like color or texture.

  • Dominant vs. Recessive: Dominant traits express while recessive require two copies.

  • Independent Assortment: Traits inherited independently if on different chromosomes.

Punnett Squares and Inheritance Calculations

  • Directions for creating 4-box Punnett squares for simple traits.

  • Calculate genotype and phenotype percentages based on parental genotypes.

Simple Patterns of Inheritance in Humans

  • Examples: Tongue rolling, hitchhiker thumb, PTC tasting, ABO blood group system.

  • Genetic Disorders: Traits controlled by single genes, e.g., cystic fibrosis, Huntington's disease.

Patterns of Complex Inheritance

  • Polygenic Traits: Multiple genes control traits with environmental influences.

  • Pleiotropic Traits: Single gene impacts multiple traits, e.g., sickle cell anemia.

  • Discussing gene behavior complexity and environmental interactions.

Further Reading (Optional)

  • Links for more information on Mendelian traits and genetic disorders.