Lecture 12, 13

• What are the main steps of meiosis?

  Meiosis I and Meiosis II
• How does meiosis contribute to genetic diversity?

  By allowing crossing-over and independent assortment
• What are the main differences between mitosis and meiosis?

  Mitosis produces identical cells, meiosis does not
• What do geneticists mean by ‘linked genes’?

  Genes that are inherited together due to proximity
• What are genes made up of?

  Segments of DNA
• How are genes passed to the next generation?

  Via reproductive cells called gametes
• What is a locus?

  A specific location of a gene on a chromosome
• What do diploid cells produce during mitosis?

  Identical diploid progeny cells
• What is karyokinesis?

  Nuclear division during cell division
• What is cytokinesis?

  Cytoplasm division during cell division
• What happens at metaphase during mitosis?

  Sister chromatids are pulled towards opposite poles
• What occurs at the beginning of anaphase in mitosis?

  The centromere is severed, chromatids separate
• How many nuclear divisions occur in meiosis?

  Two nuclear divisions
• What is the result of Meiosis I?

  Two daughter nuclei
• What happens to chromosomes in Meiosis II?

  Each daughter nucleus divides again
• What is the chromosome number in Meiosis I if 2n = 6?

  n = 3
• What occurs during crossing over in meiosis?

  DNA exchange between non-sister chromatids
• What forms during synapsis?

  A tetrad of homologous chromosomes
• What is the synaptonemal complex?

  A protein structure that holds homologous chromosomes together
• What happens to the synaptonemal complex during crossing over?

  It dissolves after crossing over occurs
• What are chiasmata?

  X-shaped regions where crossing over occurred
• What occurs during metaphase I of meiosis?

  Tetrads line up along the metaphase plate
• What happens during anaphase I?

  Homologous chromosomes move to opposite poles
• What is the result of telophase I and cytokinesis?

  Cells have half the number of chromosomes
• What occurs during prophase II?

  Chromosomes condense and the nuclear envelope breaks down
• What happens during metaphase II?

  Chromosomes align at the metaphase plate
• What occurs during anaphase II?

  Sister chromatids separate and move to opposite poles
• What is the outcome of telophase II and cytokinesis?

  Four new haploid cells are formed
• What can mistakes in meiosis lead to?

  Defective gametes and genetic abnormalities
• What is non-disjunction?

  Failure of homologs to segregate during meiosis I

  
• What is Trisomy 21?

  A common trisomy that is not lethal
• What are the main differences between mitosis and meiosis?

  • Mitosis produces identical diploid cells
  • Meiosis produces genetically diverse haploid cells
  • Mitosis involves one division, meiosis involves two
  • Sister chromatids separate in mitosis, not in meiosis I
• What are the essential concepts of meiosis?

  • Chromosomes replicate once before meiosis I
  • Homologous chromosomes connect to opposite spindle poles in metaphase I
  • Crossing-over occurs in meiosis I, contributing to genetic diversity
  • Sister chromatids separate in meiosis II
  • Fertilisation restores diploid number in zygote
  • Errors in meiosis can lead to lethal gametes
• What is genetic linkage and its importance?

  • Linked genes are inherited together due to proximity
  • Recombination frequency indicates how often genes are transmitted together
  • Linkage analysis helps locate disease genes
  • Genetic markers assist in tracking inherited diseases
• What is the difference between genetic maps and physical maps?

  • Genetic maps are based on recombination frequencies
  • Physical maps measure actual DNA distance
  • Recombination hotspots can overestimate distances
  • Low recombination rates can underestimate distances
• What are recombination hotspots?

  • Regions of DNA with high recombination frequency
  • Can affect perceived distances between genes
  • Genes flanking hotspots appear more distant on genetic maps
• What are the essential concepts regarding linked genes?

  • Linked genes do not assort independently
  • Parental gametes contain alleles from one grandparent
  • Recombinant gametes contain alleles from different grandparents
  • Genetic maps may not accurately reflect distances between genes