Cell cycles and processes

• What is mitosis?

  A type of nuclear division that produces genetically identical cells/diploid cells.
• What precedes and follows mitosis?

  Interphase and cytokinesis.
• What is mitosis important for?

  Growth- as it produces lots of cells

  Repair- it replaces damaged cells with genetically identical cells
• What are the 4 main stages of mitosis?

  Prophase, metaphase, anaphase and telophase.
• Describe interphase:

  • chromosomes not visible
  • DNA replicates at the S phase of the cell cycle
• Describe metaphase:

  • nuclear membrane disappears
  • chromosomes align along the equator of the cell
  • chromosomes attach via their centromeres to the spindle fibres
• Describe anaphase:

  • spindles contract so chromosomes split into their chromatids
  • pulled towards the poles of the cell, led by their centromeres
  • v shape
• Describe telophase:

  • chromatids reach the poles and uncoil, forming chromatin
  • nuclear membrane reforms
• Flowchart explaining what a chromosome is made up of:

  DNA -> wraps around histones -> chromatin -> tightly coils and condenses -> chromosome -> DNA replicates -> chromosome
• What are haploid cells?

  Cells that contain only one set of chromosomes.
• What are homologous pairs?

  Maternal and paternal chromosome pairs with the same size, shape and pattern. They carry the same genes but different alleles.
• Define meiosis:

  A type of nuclear division used by sexually reproducing organisms, which produces gametes (genetically different daughter cells)
• Describe the first and second divisions that occur during meiosis:

  1st- homologous chromosomes are separated so number of chromosomes halves

  2nd- sister chromatids are separated
• What is the product at the end of meiosis?

  4 haploid daughter cells
• Define cytokinesis:

  Division of the cytoplasm.
• Describe the 3 main parts of interphase:

  1. G1- this is growth of the cell and doubling of the organelles
  2. S- DNA is replicated
  3. G2- growth of the cell and preparation for cell division
• How to calculate mitotic index:

  number of cells in mitosis / total number of cells X 100
• When does independent segregation and crossing over occur?

  In the first division of meiosis.
• How do you identify meiosis in a life cycle?

  Find where a diploid cell (2n) becomes a haploid cell (n).
• How does random fertilisation increase genetic diversity?

  It shuffles genes around, and the joining of the egg and sperm is random.
• Describe the steps in independent segregation:

  1. Homologous pairs line up randomly
  2. They are then segregated
  3. This causes different combinations of maternal and paternal chromosomes in daughter cells
• How to calculate the combination of alleles as a result of independent segregation:

  2 ^ n where n= number of homologous pairs
• Define genetic variation:

  Differences between individuals of the same species due to genes / environment.
• Describe the steps in crossing over:

  1. Homologous chromosomes associate to form bivalents
  2. Non-sister chromatids bend and twist at points called chiasmata
  3. Alleles are exchanged between the non-sister chromatids
  4. This produces new combinations of alleles in chromosomes
• What does a short interphase in the cell cycle indicate?

  That cells are dividing rapidly as more are undergoing mitosis.
• What is cancer?

  Uncontrollable cell division.
• What do main cancer treatments involve?

  Controlling the rate of cell division by blocking the cell cycle.
• How do viruses replicate?

  They replicate inside host cells by injecting their nucleic acid to replicate virus particles.
• Describe the stages of binary fission:

  1. circular DNA and plasmids replicate
  2. cytoplasm divides to form 2 daughter cells
  3. each daughter cell has one copy of the circular DNA and a variable number of plasmids
• Define non-disjunction:

  Failure of the homologous chromosomes/chromatids to separate during the first/second meiotic division.
• What is the effect of non-disjunction?

  Gametes with one extra or missing chromosome.

  abnormal gamete and normal gamete fuse -> zygote has odd number of chromosomes -> as cells divide by mitosis, all cells have an abnormal chromosome number