Biology - Genetics Chapter 4

• Genetics


  study of heredity and variation of living organisms and how genetic information is passed on
• Cell theory


  all living things are composed of one or more cells, cells are the smallest units of living organisms, new cells come from pre-existing cells through cell division
• Asexual Reproduction


  production of an offspring from a single parent resulting in a genetically identical offspring
• What are the pros to asexual reproduction?

  there is no need to find a mate or have specialized anatomy
• What are two types of asexual reproduction?

  Budding - new individual develops and detaches itself once large enough

  Fragmentation - piece of organism develops into a mature individual
• Sexual Reproduction

  production of an offspring from two parent organisms --> offsprings ar enot genetically identical
• What are the benefits to sexual reproduction?

  help species survive and adapt to changes
• What are the cons to sexual reproduction?

  need specialized organs to produce sex cells, mating calls can attract both predators and mates, and inherit genes can make one weaker
• Cell Cycle


  all somatic cells (non sex cell) go through a cycle of 12-24 hours
• Three uses of cell cycle

  growth of organism, repair of damaged tissues and organs, replace/maintenance of dead/dying cells
• Three stages of cell cycle

  interphase, mitosis, and cytokinesis
• Interphase


  grows and creates genetic material copies for the next stage

  G1 - major period of growth where many new molecules are created

  S - DNA is replicated and exists as chromatin

  G2 - cell synthesizes more molecules
• Mitosis 


  cells genetic material and physical cell prepares to split. result in two cells that are genetically identical
• What are the four stages of mitosis

  prophase, metaphase, anaphase, and telophase
• Prophase

  • chromatin condenses into chromosomes --> two chromosome arms are sister chromatids
  • chromosomes are joined at the centromere
  • nuclear membrane + nucleolus breaks down
  • spindle fibres made of microtubules form from the centromeres --> move to opposite poles of the cell to form the spindle apparatus
• Metaphase

  • spindle fibres guide chromosomes to equator of the cell
  • spindle fibres attach to the centromere
• Anaphase

  • centromere splits and sister chromatid splits
  • separated sister chromatid are now chromosomes
  • move to opposite poles
• Telophase


  chromosome unwinds into chromatin and nuclear membrane/nucleus reforms
• Cytokinesis

  • cell is pinched at equator to form 2 daughter cells
  • Animal: microfilaments pinch the cytoplasm
  • Plants: a cell plate forms b/w daughter nuclei
  • Prokaryotic Cell: goes through binary fission
• DNA

  deoxyribose acid, double stranded helix,
• What are the four bases of DNA?

  Adenine, Guanine, Thymine, and Cytosine
• Chromosomes

  humans have 46 chromosomes and 23 pairs --> X and Y are the sex chromosome and the remaining are called autosomes
• Homologous Chromosomes


  appear simmilar but not genetically identical --> same banding pattern and gene but different forms (alleles)
• Karyotype


  photo of pairs of homologus chromosomes, from 1 - 22 large to small (plus X and Y at the end)
• Sexual Reproduction - Hermaphroditic Species


  produce male and female gametes
• Gamete


  male/female reproductive cell containing half the number fo chormosomes
• Zygote


  cell resulting in fusion of 2 gametes through a process called fertilization
• Diploid


  cells with pairs of chromosomes also known as the zygote
• Haploid


  cells with half the number of chromosomes also known as the gametes
• Diploid number

  2n = ? (eg. 2n = 4 --> there are four chromosomes in the diploid)
• Meiosis


  process that produces 4 cells with half the number of chromosomes as the parent cell
• What does Meiosis contribute to?

  genetic reduction: daughter cells with less chromosmes

  genetic recombination: different combination of alleles increasing genetic variety
• Interphase - Meiosis


  same as mitosis
• Meiosis 1 - Prophase 1

  • each pair of homologous chromosomes line up side by side (synapsis)
  • while lined up crossing over may occur
  • centrosome moves to poles of cell and spindle apparatus forms
• Tetrad


  two pairs of sister chromatids or 4 chromosome arms
• Chiasma


  point of intersection of two homologous chromosomes
• Meiosis 1 - Metaphase 1

  spindle fibre attaches to centromere of each homologous chromosome --> pairs line up on the equator
• Meiosis 1 - Anaphase 1


  homologous chromosomes separate and move to opposite poles --> sister chromatids do not split and the cell becomes a haploid
• Meiosis 1 - Telophase 1


  chromosomes uncoil and spindle fibre disappears --> cytokinesis occurs forming 2 haploid cells
• meiosis 2


  similar to mitosis except cells undergoing division are haploids and result in 4 haploid cells