Study Guide: Quiz 1 - Mitosis and Meiosis

Concepts to Study

Chromosomes
  1. Chromatin - Loose, uncoiled DNA found in the nucleus during interphase.

  2. Chromatid - One of two identical halves of a duplicated chromosome.

  3. Sister Chromatids - Two identical chromatids joined together at a centromere.

  4. Chromosome - Condensed, coiled DNA that carries genetic information.

Parts of a Chromosome
  • Centromere - The central region where sister chromatids are joined.

  • Chromatid - One half of a duplicated chromosome.

  • Telomere - Protective ends of chromosomes that prevent degradation.

  • Long Arm (q arm) - The longer section of a chromosome.

  • Short Arm (p arm) - The shorter section of a chromosome.

Why are telomeres important?

  • They prevent the loss of genetic information during DNA replication.

  • Shortening of telomeres is linked to aging and cell death.

Relationship between sister chromatids?

  • Sister chromatids are identical copies of the same chromosome, held together at the centromere.


Cell Cycle

Stages of the Cell Cycle
  1. Interphase (G1, S, G2)

    • G1: Cell growth and preparation for DNA replication.

    • S: DNA replication occurs.

    • G2: Final preparation for mitosis, organelles are duplicated.

  2. Mitosis - Division of the nucleus (see stages below).

  3. Cytokinesis - Division of the cytoplasm, forming two daughter cells.

Checkpoints in the Cell Cycle
  • G1 Checkpoint - Checks cell size and DNA integrity.

  • G2 Checkpoint - Ensures DNA replication was successful.

  • M Checkpoint - Verifies chromosome alignment during mitosis.

Apoptosis:

  • Programmed cell death to remove damaged or unneeded cells.

Mitosis in Single vs. Multicellular Organisms

  • Single-celled organisms: Mitosis is used for reproduction.

  • Multicellular organisms: Mitosis is used for growth, repair, and maintenance.


Stages of Mitosis

  1. Prophase - Chromatin condenses into chromosomes; nuclear envelope breaks down.

  2. Metaphase - Chromosomes align at the metaphase plate.

  3. Anaphase - Sister chromatids separate and move to opposite poles.

  4. Telophase - Nuclear envelope reforms; chromosomes decondense.

Recognizing the Stages:

  • Use images to identify chromosome alignment and nuclear envelope status.


Meiosis

Purpose of Meiosis

  • Creates gametes (sperm and egg) for sexual reproduction.

  • Introduces genetic variation.

Gene vs. Allele

  • Gene - A section of DNA that codes for a trait.

  • Allele - A variant of a gene (e.g., blue vs. brown eye color).

Sister Chromatids vs. Homologous Chromosomes

  • Sister Chromatids - Identical copies of a chromosome.

  • Homologous Chromosomes - Chromosome pairs (one from each parent) with similar genes but possibly different alleles.

Chromosome Count in Humans

  • 46 total chromosomes (23 pairs), inherited from both parents.

Diploid vs. Haploid Cells

  • Diploid (2n) - Two sets of chromosomes (body cells).

  • Haploid (n) - One set of chromosomes (gametes).

Sources of Genetic Variation

  1. Crossing Over - Exchange of DNA between homologous chromosomes in Prophase I.

  2. Independent Assortment - Random separation of chromosomes during Metaphase I.

Tetrad Formation and Breakdown

  • Tetrad - A pair of homologous chromosomes (4 chromatids) that forms during Prophase I.

  • Tetrads separate in Anaphase I, while sister chromatids separate in Anaphase II.

DNA Duplication in Meiosis

  • DNA is duplicated once, but the cell divides twice.


Oogenesis vs. Spermatogenesis

Process

Number of Gametes Produced

Oogenesis

1 egg cell, 3 polar bodies

Spermatogenesis

4 sperm cells


Mitosis vs. Meiosis Comparison

Description

Mitosis

Meiosis

Produces gametes

Growth & repair

Genetic variation

One division

Two divisions

Identical daughter cells

Synapsis of homologous chromosomes

Asexual reproduction

Four haploid gametes produced

Also called reduction division


Nondisjunction and Karyotypes

Nondisjunction:

  • Failure of chromosomes to separate properly.

  • Can occur in Meiosis I (homologous chromosomes fail to separate) or Meiosis II (sister chromatids fail to separate).

Karyotype:

  • A visual representation of chromosomes used to detect abnormalities.

  • Can reveal sex (XX or XY) and chromosomal disorders (e.g., Down syndrome - Trisomy 21).

Chromosomal Abnormalities:

  • Autosomal disorders (e.g., Down syndrome, Trisomy 18).

  • Sex chromosome disorders (e.g., Turner syndrome - XO, Klinefelter syndrome - XXY).

robot