Meiosis and Chromosome Morphology

• What process precedes meiosis?

  DNA replication
• What type of cells does meiosis produce?

  Haploid sex cells or gametes
• How many nuclear and cellular divisions occur during meiosis?

  Two successive divisions (Meiosis I and Meiosis II)
• What is formed when a sperm and egg fuse?

  A diploid zygote
• What are the key features of meiosis?

  • Two sequential cycles of nuclear and cell division (Meiosis I and II)
  • One cycle of DNA replication
  • Interkinesis: short interphase without DNA replication
  • Pairing of homologous chromosomes and recombination
  • Four haploid cells formed at the end of meiosis II
• What is the outcome of meiosis II?

  Four haploid cells
• What happens during Meiosis I?

  Homologous chromosomes segregate
• What is the role of genetic recombination in meiosis?

  It allows for the exchange of genetic information between homologous chromosomes
• What is the term for the physical exchange of genetic information during meiosis?

  Crossovers
• What occurs during the leptotene phase of prophase I?

  The homologs condense and begin to pair
• What is the synaptonemal complex and when does it begin to assemble?

  It assembles during zygotene at sites of close association between homologs
• What is the structure formed by a pair of synapsed homologous chromosomes called?

  Bivalent or tetrad
• What happens during the pachytene phase of prophase I?

  Homologs are fully synapsed along their lengths
• What are chiasmata and when can they be observed?

  Inter-homolog connections seen during diplotene
• What is crossing over and what enzyme is involved?

  It is the exchange of genetic material between homologous chromosomes, mediated by recombinase
• What marks the final stage of meiotic prophase I?

  Terminalization of chiasmata
• What occurs during metaphase I of meiosis?

  Bivalent chromosomes align on the equatorial plate
• What happens during anaphase I?

  Homologous chromosomes separate while sister chromatids remain associated
• What is the outcome of telophase I?

  The nuclear membrane and nucleolus reappear, followed by cytokinesis
• What is interkinesis?

  The stage between the two meiotic divisions
• How does meiosis II differ from meiosis I?

  Meiosis II is an equational division, while meiosis I is a reductional division
• What is the product of meiosis II?

  Four haploid cells
• What happens during prophase II?

  The nuclear membrane disappears and chromosomes become compact
• What occurs during metaphase II?

  Chromosomes align at the equator and microtubules attach to kinetochores
• What happens during anaphase II?

  Centromeres split, allowing sister chromatids to move toward opposite poles
• What marks the end of meiosis?

  Telophase II
• What is the significance of meiosis in sexually reproducing organisms?

  It conserves chromosome number across generations and increases genetic variability
• What is nondisjunction and what are its consequences?

  It is the failure of homologs to separate properly, leading to gametes with abnormal chromosome numbers
• What is the chromosome number in human somatic cells?

  46 chromosomes
• What are the two types of cells based on chromosome structure?

  Eukaryotic cells have linear chromosomes, while prokaryotic cells have circular chromosomes
• What is the International System for Human Cytogenetic Nomenclature (ISCN)?

  • Central reference for karyotyping
  • Provides rules for cytogenetic findings in laboratory reports
  • Used in fluorescence in situ hybridization (FISH)
• How are chromosomes identified in the ISCN?

  Based on size, position of centromere, and other morphological features
• What are the four types of chromosomes based on centromere position?

  • Metacentric: centromere in the center
  • Submetacentric: centromere slightly off-center
  • Acrocentric: centromere closer to one end
  • Telocentric: centromere at one end (not seen in humans)
• What are telomeres and their function?

  Telomeres are protective structures at the ends of chromosomes that prevent degradation and unnecessary recombination
• What is a karyotype?

  • A laboratory test to view an individual's complete set of chromosomes
  • Optimal viewing occurs during metaphase
• What is the appearance of chromosomes in a scanning electron microscope (SEM)?

  Chromosomes appear uncondensed in the nucleus and condensed in the X structure
• What is the role of histones in chromosomes?

  Histones provide structural support for chromosomes
• What is the function of the centromere?

  It is the constriction point of a chromosome
• What is the significance of chromosome segregation errors during meiosis?

  They can lead to conditions such as spontaneous abortion and mental retardation
• How does maternal age affect segregation errors during meiosis?

  Segregation errors increase with advancing maternal age