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

Mitosis vs. Meiosis Comparison

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).