Sexual Reproduction and Meiosis24

Chapter 11: Sexual Reproduction and Meiosis

Background Information

  • Gametes:

    • Sexually reproducing cells.

    • Types: Egg cell (female) and sperm cell (male).

  • Fertilization:

    • Fusion of sperm and egg cells to form a zygote.

  • Zygote:

    • The single cell resulting from fertilization.

  • Homologous Chromosomes:

    • Chromosomes that are the same length and shape.

    • Carry the same genes in the same order.

Chromosome Types

  • Diploid:

    • Cells have two copies of each chromosome (one from each parent).

  • Haploid:

    • Cells have only one copy of each chromosome.

  • Germ-line Cells:

    • Cells that produce gametes.

  • Somatic Cells:

    • Cells that form body parts.

Chromosome Function

  • Autosomes:

    • Determine non-sex characteristics of an individual.

  • Sex Chromosomes:

    • Determine the sex of an individual.

    • XX indicates females; XY indicates males.

Meiosis Overview

  • Meiosis Definition:

    • Nuclear division that produces genetically unique cells.

    • Results in four haploid cells from one diploid cell.

    • Occurs in sex cells (sperm and egg).

    • Involves reduction division and crossing over.

  • Crossing over:

    • Exchanging of genetic information between homologous chromosomes.

Meiosis Stages

  • Meiosis I:

    • Separation of homologous chromosomes.

  • Meiosis II:

    • Separation of sister chromatids.

Interphase

  • Description:

    • The phase where genetic material and cellular components replicate:

      • Centrioles

      • Chromatin

      • Plasma membrane

      • Nucleolus

      • Nuclear envelope

Prophase I

  • Events:

    • Chromatin condenses to form chromosomes.

    • Nuclear envelope disappears.

    • Spindle formation occurs.

    • Synapsis: alignment of homologous chromosomes.

    • Chiasmata: Sites of crossing over.

Metaphase I

  • Action:

    • Homologous chromosomes align at the center of the cell.

Anaphase I

  • Process:

    • Homologous chromosomes are separated and move towards opposite poles.

Telophase I

  • Outcome:

    • Chromosomes loosen, nuclear envelope re-forms.

    • Cytokinesis may occur, leading to cells with half the genetic info.

Interkinesis

  • Description:

    • A brief interphase without DNA replication.

    • Results in haploid daughter cells.

Prophase II

  • Process:

    • Two haploid cells undergo meiosis again.

Metaphase II

  • Action:

    • "Not so" sister chromatids line up in the center of the cell.

Anaphase II

  • Process:

    • Sister chromatids are separated and move to opposite poles.

Telophase II

  • Outcome:

    • Results in four haploid daughter cells.

Summary of Meiosis

  • Phases Overview:

    • Interphase: Preparation phase.

    • Meiosis I: Homologous chromosomes pair and separate.

    • Meiosis II: Sister chromatids separate.

    • Tetrads form during synapsis. Four haploid cells are produced.

Chapter 13.4: Genetic Disorders

Errors in Chromosome Numbers

  • Polyploid Cells:

    • Contain extra complete sets of chromosomes.

    • Not viable in humans; can occur in plants (e.g., strawberries).

  • Aneuploidy:

    • Cells have extra or missing chromosomes due to nondisjunction.

Non-disjunction

  • Definition:

    • Failure of homologous chromosomes to separate during meiosis.

    • Results in individuals having too much or too little genetic information.

Genetic Disorders from Non-disjunction

  • Trisomy 21:

    • Caused by non-disjunction leading to three copies of chromosome 21.

    • Results in Down Syndrome.

  • Trisomy 18:

    • Caused by three copies of chromosome 18.

    • Results in Edwards Syndrome.

Other Genetic Disorders

  • Turner Syndrome:

    • Forms from non-disjunction of sex chromosomes (XO).

    • Characteristics: Sterility, small stature, potential mental impairment.

  • Trisomy X:

    • Female with three X chromosomes (XXX) who is normal.

  • Klinefelter Syndrome:

    • Male with two X chromosomes and one Y (XXY).

    • Characteristics: Sterile, mixed secondary sexual traits.

  • Jacob’s Syndrome:

    • Male with two Y chromosomes (XYY).

    • Typically considered normal.

Exam Information

  • Exam Date: December 3rd, 2024

  • End of Exam Four Info.