Unit 5:Lesson 1

Unit 5: Heredity

Lesson Overview

  • Lesson 1: Meiosis and Reproduction

  • Lesson 2: Mendelian Genetics

  • Lesson 3: Non-Mendelian Genetics and Pedigrees

Family Traits

  • Traits discussed: Eyes, Hair, Ears

  • Family members involved: Dad, Son, Mom

Lesson 1: Meiosis & Reproduction

Aim

  • How do organisms transmit genetic information between generations?

Think-Pair-Share Question

  • Discuss the implications of mutations in somatic vs gamete cells.

  • Are mutations in somatic (body) cells or gamete (sex) cells more detrimental? Why?

Topic 5.1: Meiosis

Learning Objectives

  • IST-1.F: Explain how meiosis results in chromosome transmission from one generation to the next.

  • IST-1.G: Describe similarities/differences between mitosis and meiosis phases and outcomes.

Key Definitions

  • Describe: Note characteristics of a concept.

  • Explain: State why or how something happens, more demanding than describing.

Topic 5.2: Meiosis and Genetic Diversity + Chromosomal Inheritance

Learning Objectives

  • IST-1.H: Explain how meiosis generates genetic diversity.

  • SYI-3.C: Explain how chromosomal inheritance generates variation in sexual reproduction.

Important Vocabulary

  • Gamete: A haploid sex cell (e.g., sperm and egg).

  • Haploid: A cell with half the normal number of chromosomes (23 in humans).

  • Somatic Cell: A diploid body cell (e.g., heart, skin, lung cells).

  • Diploid: A cell with a full set of chromosomes (46 in humans).

  • Homologous Chromosome: Similar structure and genes, one from each parent.

  • Crossing Over: Homologous chromosomes exchange genes.

  • Genetic Diversity: Variability in traits among organisms.

Major Reproductive Strategies

Asexual Reproduction

  • Does not involve gamete production/fusion.

  • Mitosis-like process forms genetically identical offspring.

  • Pros: Auto-adaptation to environment, no mate needed, fast reproduction.

  • Cons: Potential overpopulation, limited genetic diversity.

Sexual Reproduction

  • Requires meiosis and mitosis for gamete production/fusion.

  • Fertilization forms a zygote from gametes.

  • Pros: Genetic diversity, appealing offspring.

  • Cons: Requires time/energy, may lead to challenges in mate finding.

Karyotypes

Definition

  • A display of chromosome pairs ordered by size and length.

  • Comprises homologous duplicated chromosomes.

Cells and Chromosomes

Eukaryote Structure

  • DNA packaged in chromosomes, two types exist:

  • Autosomes: Chromosomes not determining sex (22 pairs in humans).

  • Sex chromosomes: X and Y (Eggs: X, Sperm: X or Y).

Life Cycles

  • Sequence of stages from conception to reproduction.

  • Fertilization alternates with meiosis in sexual life cycles.

    • Fertilization merges haploid sperm with haploid egg to form a diploid zygote.

Meiosis Overview

  • Creates haploid gametes in diploid organisms.

  • Results in daughter cells with half the chromosomes of the parent cell (e.g., humans’ sperm and eggs, n=23).

  • Involves two rounds of division: Meiosis I and II.

Meiosis vs. Mitosis

Mitosis

  • One round of division.

  • Occurs in somatic cells.

  • Starts and ends with the same number of chromosomes (diploid).

  • Produces two identical daughter cells.

Meiosis

  • Two rounds of division.

  • Occurs in gametes.

  • Starts and ends with a different number of chromosomes (haploid).

  • Produces four genetically distinct daughter cells.

Similarities

  • Chromosomal segregation process is similar (chromosomes line up, are pulled apart, etc.).

Key Events in Meiosis

  1. Prophase I: Synapsis and crossing over.

  2. Metaphase I: Tetrads align at the metaphase plate.

  3. Anaphase I: Homologous pairs separate.

Meiosis I Stages

  • Interphase: Cell prepares (G1, S, G2).

  • Prophase I: Homologous chromosomes pair and form tetrads; crossing over occurs.

  • Metaphase I: Tetrads align at the metaphase plate.

  • Anaphase I: Homologous chromosomes separate while sister chromatids stay attached.

  • Telophase I & Cytokinesis: Cell divides, resulting in haploid daughter cells.

Meiosis II Stages

  • Prophase II: Spindle forms, no crossing over.

  • Metaphase II: Chromosomes align at the metaphase plate; chromatids are unique.

  • Anaphase II: Sister chromatids separate to opposite poles.

  • Telophase II & Cytokinesis: Forms 4 genetically unique haploid cells.

Genetic Variation from Meiosis

  1. Crossing Over: Produces recombinant chromosomes, exchanges genetic material.

  2. Independent Assortment: Random orientation of chromosomes during metaphase I.

  3. Random Fertilization: Any sperm can fertilize any egg, leading to unique combos.

Chromosomal Mutations

Consequences of Meiosis Errors

  • Genetic disorders can stem from single affected alleles or chromosomal mutations like nondisjunction.

  • Only mutations in gametes are passed to offspring.

  • Severe mutations impact entire gene sections or chromosomes.

Types of Chromosomal Mutations

  1. Deletions: Missing chromosome sections.

  2. Duplications: Doubled sections.

  3. Inversions: Reversed gene sequences.

  4. Insertions: Part of a chromosome inserted into another.

  5. Translocations: Non-homologous chromosomes exchanging alleles.

Nondisjunction

  • Occurs when homologous chromosomes fail to separate.

  • Leads to gametes with abnormal chromosome numbers.

Consequences of Nondisjunction

  • Genetic diseases diagnosed via karyotypes.

  • Abnormal fertilization leads to severe genetic disorders like trisomy and monosomy.

Practice Questions

  1. Identify the false statement about sexual reproduction.

  2. Determine when crossing over occurs.

  3. Identify when the diploid number of chromosomes is restored.