DNA and Chromosomes in Eukaryotes
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Questions and Answers

What structure attaches sister chromatids to each other?

  • Histone
  • Centromere (correct)
  • Chromosome
  • Chromatin

    • Which process produces four haploid cells?

  • Mitosis
  • Binary fission
  • Cytokinesis
  • Meiosis (correct)

    • What term describes one of a pair of chromosomes with the same gene sequence?

  • Centromeres
  • Alleles
  • Sister chromatids
  • Homologous chromosomes (correct)

    • Which of the following statements about sister chromatids is true?

    <p>They are identical copies of the same chromosome.</p> Signup and view all the answers

    What is the total number of chromosomes in a human somatic cell?

    <p>46</p> Signup and view all the answers

    What is the primary purpose of meiosis?

    <p>To produce haploid cells for reproduction</p> Signup and view all the answers

    At what stage in females does Meiosis II typically occur?

    <p>During fertilization</p> Signup and view all the answers

    How do homologous chromosomes differ from sister chromatids?

    <p>Homologous chromosomes come from each parent; sister chromatids are formed during DNA replication</p> Signup and view all the answers

    Which process contributes to genetic variation during meiosis?

    <p>Independent assortment of chromosomes</p> Signup and view all the answers

    What is the karyotype of a human individual?

    <p>An image showing an individual's chromosomes arranged in numerical order</p> Signup and view all the answers

    What is the primary outcome of crossing over during meiosis?

    <p>Creation of new allelic combinations</p> Signup and view all the answers

    During which phase of meiosis are homologous chromosomes separated?

    <p>Anaphase I</p> Signup and view all the answers

    What does the Law of Independent Assortment state?

    <p>Different genes are inherited independently of each other</p> Signup and view all the answers

    What is the end result of meiosis I in terms of chromosome number?

    <p>n</p> Signup and view all the answers

    In which phase of meiosis does crossing over occur?

    <p>Prophase I</p> Signup and view all the answers

    How many viable gametes are produced by oogenesis?

    <p>1 egg and 3 polar bodies</p> Signup and view all the answers

    What role does the synaptonemal complex play during meiosis?

    <p>Facilitates crossing over between non-sister chromatids</p> Signup and view all the answers

    What describes the outcome of meiosis II?

    <p>Results in four haploid gametes</p> Signup and view all the answers

    Study Notes

    DNA - Eukaryotes

    • Found in the nucleus
    • DNA is wound around histone proteins, which helps compact DNA into the nucleus.
    • Chromatin: DNA in a loose, uncoiled form. Considered active.
    • Chromosomes: Tightly coiled and condensed DNA. This occurs during cell division.

    Chromosomes

    • Chromatid: A single strand.
    • Chromosome: Consists of two chromatids joined at the centromere.
    • Centromere: The location on a chromosome where two chromatids are attached.

    Homologous Chromosomes

    • Homologous chromosomes are pairs of chromosomes that have the same genes, length, and centromere location.
    • One chromosome from each pair comes from the father, and the other comes from the mother.
    • Humans have 23 pairs of chromosomes (46 total).
    • Autosomes: Any chromosome that is not a sex chromosome.
    • Sex Chromosomes: The X or Y chromosomes.

    Mitosis

    • Sister chromatids separate.
    • Sister chromatids are identical.

    Sister Chromatids

    • Two identical copies of the same chromosome.
    • Formed by DNA replication and are attached by the centromere.
    • During cell division, they are separated.
    • Each daughter cell receives one copy.

    Mitosis

    • Eukaryotes
    • Asexual
    • DNA is replicated
    • Produces 2 diploid cells.

    Meiosis

    • Eukaryotes
    • Sexual
    • 2 cell divisions
    • Produces 4 haploid cells.

    Meiosis I & II

    Meiosis I

    • Prophase I: Synapsis occurs to form a tetrad (crossing over). This contributes to variation.

    • Metaphase I: Independent assortment occurs. This contributes to variation.

    • Anaphase I: Homologous chromosomes segregate to opposite poles.

    • Telophase I: Cytoplasm divides.

    • Meiosis I starts with 2n, and ends with 1n.

    Meiosis II

    • Prophase II: Chromosomes condense.

    • Metaphase II: Chromosomes line up at the middle of the cell.

    • Anaphase II: Sister chromatids separate and move to opposite poles.

    • Telophase II: Cytoplasm divides.

    • Meiosis II starts with 1n and ends with 1n.

    Homologues

    • Meiosis I: Homologues (homologous chromosomes) are separated.

    Sister Chromatids

    • Meiosis II: Sister chromatids (are separated, similar to mitosis).

    Crossing Over

    • The exchange of genetic material between non-sister chromatids.
    • This occurs during prophase I (meiosis I).
    • Results in new combinations of alleles in daughter cells.
    • Synaptonemal complex: Facilitates crossing-over between non-sister chromatids.

    Variation

    • Crossing Over: The exchange of genetic material between non-sister chromatids results in new allelic combinations.
    • Independent Assortment: The random segregation of chromosomes during meiosis I contributes to genetic variation.
    • Random fertilization: The random combination of sperm and egg during fertilization contributes to genetic variation.

    Independent Assortment

    • The law of independent assortment states that different genes and their alleles are inherited independently.
    • Genes on a chromosome can rearrange themselves through crossing-over.
    • Each gene is inherited independently.

    Meiosis

    • Gametogenesis: The production of sperm (spermatogenesis) and eggs (oogenesis), this occurs via meiosis.
    • Sperm: Meiosis produces 4 equal sperm.
    • Egg: Meiosis produces 3 polar bodies and one egg. This is an unequal division.

    Summary

    • Produces haploid cells (gametes), which are 1n.
    • Genetic variation occurs via crossing over during Prophase I.
    • Meiosis I is reduction division
    • Meiosis II is equational division
    • Males: Occurs at the start of puberty.
    • Females: Meiosis I occurs before birth. Meiosis II occurs at puberty or fertilization.

    Zygotes

    • Zygote (2n) - A fertilized egg, it is diploid.
    • Fertilization: The fusion of sperm (1n) and oocyte (1n) to form a zygote.

    Human Chromosomes

    • 23 pairs total: one from each parent.
    • Karyotype: A complete set of chromosomes arranged in numerical order.

    Learning Objectives

    • Explain the process of meiosis.
    • Explain why meiosis is important for sexual reproduction.
    • Compare and contrast sister chromatids and homologous chromosomes.
    • Describe the stages of meiosis.
    • Differentiate between a zygote and a gamete.
    • Compare and contrast mitosis and meiosis.
    • Explain how crossing over occurs and how it contributes to genetic variation.
    • Explain what a germ-line cell is and its role in gametogenesis.
    • Explain how chromosomes are duplicated and separated during mitosis and meiosis.

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    Related Documents

    Meiosis Lecture 20 (Spring 2024) PDF

    Description

    This quiz covers essential concepts related to DNA and chromosomes in eukaryotic cells, including chromatin, homologous chromosomes, and the process of mitosis. Test your understanding of key terms such as chromatids, centromeres, and the role of histone proteins in DNA compaction. Perfect for biology students studying cell structure and division.

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