Quiz on Meiosis and Karyotypes

Quiz on Meiosis and Karyotypes

• Describe the number and organization of human chromosomes in a typical somatic cell. Distinguish between autosomes and sex chromosomes. (8.11 and links below)

  • Somatic Cell: 46 chromosomes (23 pairs)

    • They are condensed enough to be viewed with a microscope and arranged into matching pairs

      • Autosomes: chromosomes other than sex chromosomes (44 of them in humans) are organized with a twin that resembles it in length, centromere position, and staining pattern.

      • Sex Chromosomes: they determine an individual’s sex and are always in the 23rd chromosome spot; human females have a homologous pair of X chromosomes (XX), but males have one X and one Y which are partly homologous.

• Distinguish between somatic cells and gametes and between diploid cells and haploid cells. (8.12)

  • Somatic Cells: most animals and plants contain pairs of homologous chromosomes (diploid = 2n)

    • Ex. for humans the diploid number is 46 (2n=46)

  • Gametes: egg and sperm cells each have a single set of chromosomes (haploid = n)

    • Ex. for humans the haploid number is 23 (n=23)

• Explain why sexual reproduction requires meiosis. (8.13)

  • It is is required to maintain a constant number of chromosomes in each species from one generation to the next

• List the phases of meiosis I and meiosis II and describe the events characteristic of each phase. Recognize the phases of meiosis from diagrams and micrographs. (8.13)

  • Meiosis I

    • Prophase I - homologous chromosomes form tetrads, nonsister chromatids of each homologous pair of chromosomes exchange segments (crossing over), the chromosomes condense, the nuclear membrane disintegrates, centrioles move to opposite poles

    • Metaphase I - homologous pairs line up at the metaphase plate, spindles are attached to the centromeres

    • Anaphase I - homologous chromosomes separate through the shortening of spindle fibers attached to the centromere and lengthening to separate the poles

    • Telophase I and Cytokinesis - chromosomes decondense, nuclear membrane reforms around each set of chrosomes, the cytoplasm divides splitting each cell into 2 cells

RESULTS OF MEIOSIS I = 2 Haploid Cells

• Meiosis II (essentially the same as mitosis but starts with a haploid cell))

  • Prophase II - the chromosomes condense, the nuclear membrane disintegrates, centrioles move to opposite poles

  • Metaphase II - individual chromosomes line up at the metaphase plate, spindles are attached to the centromeres

  • Anaphase II - sister chromatids separate and become individual chromosomes through the the shortening of spindle fibers attached to the centromere and lengthening to separate the poles

  • Telophase II and Cytokinesis - chromosomes decondense, nuclear membrane reforms around each set of chrosomes, the cytoplasm divides splitting each cell into 2 cells

RESULTS OF MEIOSIS II = 4 Haploid Gametes

• Describe the similarities and differences between mitosis and meiosis. Explain how the result of meiosis differs from the result of mitosis. (8.14)

  • Similarities

    • Prophase

      • Nuclear envelope breaks down

      • Centrioles move to opposite poles

      • Chromosomes condense

    • Metaphase

      • Spindle has formed (chromosomes are attached)

    • Anaphase

      • Spindle fibers shorten (some lengthen to separate poles)

    • Telophase

      • Nuclear membrane reforms around each set of chromosomes

      • Chromosomes decondense

    • Cytokinesis

      • Cytoplasm divides splitting each cell into 2 cells

  • Differences

    • Prophase - each duplicated chromosome remains separate

    • Prophase I - homologous chromosomes form tetrads and cross over

    • Metaphase - duplicated chromosomes line up singly

    • Metaphase I - duplicated homologous chromosomes line up in pairs

    • Anaphase - sister chromatids separate

    • Anaphase I - homologous chromosomes separate

Others:

Mitosis involves one division of the nucleus and cytoplasm while meiosis involves two divisions.

Mitosis starts with a diploid cell, meiosis II starts with haploid cells

Mitosis produces 2 daughter cells, meiosis produces 4 daughter cells

• Explain how independent orientation of chromosomes at metaphase I, random fertilization, and crossing over contribute to genetic variation in sexually reproducing organisms. (8.15-8.17)

  • Independent orientation: Chromosome pairs line up randomly in meiosis, creating different combos of mom’s and dad’s genes.

  • Crossing over: Chromosomes swap pieces, mixing genes and making each chromosome unique.

  • Random fertilization: Any sperm can meet any egg, making each baby genetically different

• Define nondisjunction, explain how it can occur, and describe what can result (8.18).

  • Nondisjunction is when chromosomes don’t separate properly during meiosis.

  • It can happen in meiosis I (homologous chromosomes fail to separate) or meiosis II (sister chromatids fail to separate).

  • This can result in gametes with too many or too few chromosomes, leading to disorders like Down syndrome (extra chromosome 21).

• Explain how and why karyotyping is performed (8.19).

  • Karyotyping is a process where scientists take a picture of a person's chromosomes, arrange them in pairs, and check for abnormalities.

  • It’s done by collecting cells (like from blood), stopping them during cell division, and staining the chromosomes so they can be seen under a microscope.

  • Karyotyping is used to diagnose genetic disorders (like Down syndrome) and to check for extra, missing, or damaged chromosomes.

• Describe the main types of chromosomal alterations (8.23).

  • Deletion - a segment of a chromosome is removed

  • Duplication - a segment of a chromosome is copied and inserted into the homologous chromosome

  • Inversion - a segment of a chromosome is removed and then reinserted opposite to its original orientation

  • Reciprocal translocation - segments of two nonhomologous chromosomes swap locations with each other