Biology Notes

~~notes from General Biology I for Science Majors~~

Transformed   bacteria   revealed   the   link  between   genes   and   DNA

  Genes -  heritable   information   storage   units

 Chromosomes -  threadlike   structures   containing   genes

 DNA  is  composed   of  four  nucleotides Nucleotides   of  DNA  are   made   of:
-Phosphate   group
-Deoxyribose   (sugar)
- 1  nitrogen-containing   base
  either:
Adenine   (A)
Guanine   (G)
Thymine   (T)
Cytosine   (C)

 The  DNA  of  any  species   contains   equal   amounts   of  adenine   and  thymine   and   equal   amounts   of  guanine   and   cytosine

  DNA  is  a  double   helix  of  two  nucleotide   strands

 Sugar-Phosphate   Backbone -  a major   feature   of  DNA  structure,  formed   by  attaching   the   sugar   of  one   nucleotide   to  the   phosphate  from   the   adjacent   nucleotide   in  a  DNA  strand

 Hydrogen   bonds   between   complementary   bases   hold  the   two DNA  strands   together

 The  two  strands   of  the  DNA  double   helix  are   oriented   in  opposite  directions

 Complementary   Base   Pairs -  in  nucleic   acids,   bases   that   pair   by hydrogen   bonding,   in  DNA  adenine   is  complementary   to  thymine  and   guanine   is  complementary   to  cytosine

 The  order   of  nucleotides   in  DNA  can  encode   vast   amounts   of information

 The  replication   of  DNA  is  a  critical   event   in  a  cell’s  life DNA  replication -  is the   coping   of  the   double-stranded   DNA molecule,   producing   two  identical   DNA  double   helices

 DNA  replication   produces   two  DNA  double   helices,   each   with   one old   strand   and one   new   strand

 DNA  Helicases -  enzymes   that   pull  apart   the   parental   DNA double   helix  so  that   the   two  bases   of  the   two  DNA  strands   are   no longer   forming   base   pairs   with   each   other

 DNA  polymerases -  enzymes   that   move  along   each   separated  parental   DNA  strand,   matching   bases   on  the   strand   with  complementary   free   nucleotides,   “an   enzyme   that   makes   a  DNA polymer”

 DNA  Helicase   separates   the   parental   DNA  strands

 DNA  polymerase   synthesizes   new   DNA  strands

 Segments   of  DNA  are  joined   together   by  DNA  ligase

 Semiconservation   Replication -  the   process   of  replication   of  the  DNA  double   helix;  the   two  DNA  strands   separate   and   each   is  used as   a  template   for  the   synthesis   of  a  complementary   DNA  strand

 Cell   Cycle -  the   sequence   of  activities   that  occur   from   one   cell  division   to  the   next Asexual   Reproduction -  reproduction   that  does   not  involve   the   fusion   of  haploid   sex  cells,  the   parent   body may  divide   and   new  parts   regenerate,   or  a  new,   smaller  individual   may   form   as  an  attachment   to  the   parent,   to  drop   off when   complete

  The  prokaryotic   cell  cycle   consists   of  growth  and   binary   fission Binary   Fission -  cell  division   of  prokaryotic  cells,   “splitting   in  two”,   process   by  which   a  single   bacterium  divides   in  half,  producing   two  identical   offspring The  eukaryotic   cell  division   consists   of interphase   and   cell  division During   interphase   the   eukaryotic   cells  grows  in  size   and   replicates   its  DNA

Interphase -  first   stage   of  eukaryotic   cell cycle,   cell  acquires   nutrients   from   its  environment,   grows,   and  duplicates   its  chromosomes Cell   Division -  second   stage   of  eukaryotic   cell cycle,   one   copy  of  each   chromosome   and   usually  about   half  the  cytoplasm   and   organelles   are   parceled   out  into  each   of  the   two daughter   cells Subphases   of  Interphase G1 Gap   1 Growth   phase   I S Synthesis DNA  synthesis G2 Gap   2 Growth   phase   II G0 Gap   0 When   cell  specialize

 Differentiation-  the   process   whereby   relatively  unspecialized  cells,   especially   of  embryos,   become   specialized   into  particular  tissue   types

  There   are  two  types   of  cell  division   in  eukaryotic   cells:  Mitotic  cell   division   and   Meiotic   cell  division

 Mitotic   cell   division -  consists   of  a  nuclear   division   (mitosis)  followed   by  cytoplasmic   division   (cytokinesis)

 Mitosis   =   Greek     “thread”

  Cytokinesis   =   Greek   “cell  movement”

 Meiotic   cell   division -  meiosis   followed   by  two  cytokinesis’,  in gamete   cells

 Meiosis -  a type   of  cell  division   by  eukaryotic   organisms,   in  which   a diploid   cell  divides   twice   to  produce   four   haploid   cells

 Gametes -  the   four  haploid   (daughter)   cells  of  meiosis

 The  eukaryotic   chromosome   consists   of  a  linear   DNA  double   helix bound   to  proteins

 Locus -  the   physical   location   of  a  gene   on  a  chromosome

  Telomeres -  Greek   “end   body”,  located   at  the   ends   of  a chromosome,   repeated   nucleotide   sequences,   essential   to chromosome   stability

 Centromere -  Greek   “middle   body”,  the   region   of  a  replicated  chromosome   at  which   the  sister   chromatids   are   held   together  until   they   separate   during   cell  division
Eukaryotic   chromosomes   usually  occur   in  homologous   pairs   with  similar   genetic   information

 Karyotype -  the entire   set  of  chromosomes   from   a  single   cell

  Homologues   /  Homologous   Chromosomes -  Greek   “to  say  the same   thing”,   chromosomes   that   contain   the   same   genes

 Diploid -  “double”,   cells  with   pairs   of  homologous   chromosomes

 Autosomes -  chromosomes   that   have   a similar   appearance,  similar   genetic   composition,   and   are   paired   in  diploid   cells  of  both sexes

 Sex  Chromosomes -  pairs   of  chromosomes   that   usually  determine the   sex  of  an  organism

 Haploid -  “half”,  cells   that   contain   only  one   of  each   type   of chromosome

Four   Phases   of  Mitosis
1. prophase
2. metaphase
 3. anaphase
4. telophase

 During   prophase,   the   chromosomes   condense   and   the  spindle  microtubules   form   and   attach   to  the   chromosomes

  Prophase -  Greek   “the   stage   before”,   the first   phase   of  mitosis,   major  events   are   duplicated   chromosomes   condense,   the   spindle  microtubules   form,   chromosomes   are   captured   by  spindle

 Spindle   Microtubules -  microtubules   organized   in  a  spindle  shape   that   separate   chromosomes   during   mitosis   or  meiosis

 Centrioles -  in  animal   cells  a  short,   barrel-shaped   ring   consisting  of  nine   microtubule   triplets,   a  microtubules-containing   structure  at   the   base   of  each   cilium   and   flagellum,   gives   rise   to  the  microtubules   of  cilia  and   flagella   and   is  involved   in  spindle  formation   during   cell  division

 Kinetochore -located   at  the   centromore,   protein-containing  structure   of  each   sister   chromatid,   serves   as  an  attachment   site  for   the   ends   of  spindle   microtubules

 During   metaphase,   the   chromosomes   align   along   the   equator   of the   cell

 During   anaphase,   sister   chromatids   separate   and   are   pulled   to opposite   poles   of  the   cell

  During   telophase,   nuclear   envelopes   form   around   both   groups   of chromosomes

During   cytokinesis,   the   cytoplasm   is  divided   between   two daughter   cells

 Mutations   in  DNA  are   the  ultimate   source   of  genetic   variability

  Alleles -  formed   by  mutations,   alternate   forms   of  a  given   gene,  may  produce   differences   in  structure   or  function

 Sexual   reproduction   may  combine   different   parental   alleles   in  a single   offspring

 Meiosis   separates   homologous   chromosomes   producing   haploid  daughter   nuclei

 Meiotic   cell  division   followed   by  fusion   of  gametes   keeps   the  chromosome   number   constant   from   generation   to  generation

 Meiosis   I  separates   homologous   chromosomes   into  two  haploid  daughter   nuclei

 During   Prophase   I,  homologous   chromosomes   pair   up  and  exchange   DNA

 During   Metaphase   I,  paired   homologous   chromosomes   line  up  at the   equator   of  the   cell

 Chiasmata   (Chiasma) -  the point   at  which   a  chromatid   or  one chromosome   crosses   with   a  chromatid   of  the   homologous  chromosome   during   prophase   I,  the   site   of  exchange   of chromosomal   material   between   chromosomes

 Crossing   Over-  the   exchange   of  corresponding   segments   of  the  chromatids   of  two  homologous   chromosomes   during   meiosis

 Recombination -  the   formation   of  new   combinations   of  alleles   on a  chromosome

 During   Anaphase   I,  homologous   chromosomes   separate

  During   Telophase   I,  two  haploid   clusters   of  duplicated  chromosomes   form

 Meiosis   II  separates   sister   chromatids   into  four   daughter   nuclei

 The  life  cycle  of  most   organisms   includes   both   meiosis   and   mitosis

 The shuffling   of  homologues   creates   novel  combinations   of chromosomes

 Crossing   over   creates   chromosomes   with   novel  combinations   of genes

 Fusion   of  gametes   adds   further   genetic   variability   to  the   offspring

Locus -  a  gene’s   specific  physical   location   on  a  chromosome
Homologous   chromosomes   carry   the  same   genes   at  the  same   loci

 Alleles -  the   difference   in  nucleotide   sequences   at  the   same   gene  locus   on  two  homologous   chromosomes   produce   alternative  versions   of  the   gene

 Homozygous -  if  both   homologous   chromosomes   in  an  organism  have   the   SAME  allele   at  a  given   gene   locus,   from   the   Greek  “same   pair”

 Heterozygous -  if  two  homologous   chromosomes   have   different  alleles   at   a  given   locus,   from   the   Greek   “different   pair”

 Hybrid-  an  organism   that   is  the   offspring   of  parents   differing   in at   least   one   genetically   determined   characteristic;   also   used   to refer   to  the   offspring   of  parents   of  different   species

Keys   to  Successful   Experiments   in  Biology
-choosing   the   right   organism   with   which   to  work
- designing   and   performing   the   experiment   correctly
- analyzing   the   data   properly

 Pollen   contains   flower   sperm

 Stamens -  male  reproductive   structures   of  flowers

 Carpel -  female   reproductive   structures   of  flowers

 The  flower   egg  is  located   in  the   ovary   at  the   base   of  the   carpel

 Self-fertilization -  the   union   of  sperm   and   egg   from   the   same  individual

 True-breeding -  pertaining to an individual whose offspring produced through self-fertilization are identical to the parental type.  

True-breeding   individuals   are   homozygous   for  a  given   trait

 Cross-fertilization -  the   union   of  sperm   and   egg   from   two individuals   of  the   same   species

  The  inheritance   of  dominant   and   recessive   alleles   on  homologous  chromosomes   can   explain   the   results   of  Mendel’s   crosses

 Each  trait   is  determined   by  pairs   of  discrete   physical   units:   genes

 Each  individual   has   two  alleles   for  a  given   gene

 One  gene   per  homologous   chromosome

 The  pairs   of  genes   on  homologous   chromosomes   separate   from  each   other   during   gamete   formation,   each   gamete   receives   only one   allele   of  an  organism’s   pair   of  genes

Law  of  Independent   Assortment -  the independent   inheritance   of  two  or  more   distinct   traits;   states   that the   alleles   for  one   trait   may   be  distributed   to  the   gametes  independently   of  the   alleles   for  other   traits Mendel’s   work   went   unrecognized   after   he published   in  1865   until  Carl  Correns,   Hugo   de  Vries,  and   Erich  Tschermak   independently   and   without   knowledge   of  Mendel’s work   rediscovered   the   principles   of  genetics   in  1900,   when   they  published   they   graciously   acknowledged   the   importance   of Mendel’s   work Genes   on  the   same   chromosome   tend   to  be inherited   together

Genetic   Linkage -  the   inheritance   of  certain  genes   as  a  group   because   they  are   on  the   same   chromosome,  linked   genes   do  NOT  show   independent   assortment recombination   can   create   new   combinations   of linked   alleles

Crossing   Over -  the   exchange   of corresponding   segments   of  the   chromatids   of  two  homologous  chromosomes   during   meiosis

Genetic   Recombination -  the   generation   of new   combinations   of  alleles   on  homologous   chromosomes   due   to the   exchange   of  DNA  during   crossing   over

Sex   Chromosomes -  the   pair   of  chromosomes  that   usually   determine   the   sex  of  an  organism

Autosomes -  a  chromosome   that   occurs   in homologous   pairs   in  both   males   and   females   and   that   does   not bear   the   genes   determining   sex

  Sex-linked   genes   are   found   only  on  the   X  or  only  on  the   Y chromosome

  Sex-linked -  referring   to  a  pattern   of  inheritance   characteristic   of genes   located   on  one   type   of  sex  chromosomes   (for  example,   X) and   not  found   on  the   other   type   (for  example,   Y);  also  called   X-linked;   in  sex-linked   inheritance,   traits   are   controlled   by  genes  carried   on  the   X  chromosome;   females   show   the   dominant   trait  unless   they   are   homozygous   recessive,   where-as  males   express  whichever   allele   is  on  their   single   X  chromosome

 The  gene   for  eye  color  must   be  located   on  the  X  chromosome   and     the   Y  chromosome   has   no  corresponding   gene


Thomas   Hunt   Morgan's   hypothesis   regarding  Drosophila  fly experiments   (early   1900s):   with   one  corresponding   gene   on  the   Y chromosome,   the   F2  males   displayed   the   phenotype   determined  by  the   allele   on  the   X  chromosome

 Most  traits   are   influenced   in  varied   and   subtle   ways;  not  just   one  gene   controlling   and   one   allele   dominant   to  another

 Incomplete   dominance:   the   phenotype   of  heterozygotes   is intermediate   between   the   phenotypes   of  the   homozygotes

 Incomplete   dominance -  a  pattern   of  inheritance   in  which   the  heterozygous   phenotype   is  intermediate   between   the   two homozygous   phenotypes

  A single   gene   may  have   multiple   alleles

 Multiple   Alleles -  as  many   as  dozens   of  alleles   are produced   for  every gene   as  a  result   of  different   mutations

 Codominance -  the  relation   between   two  alleles   of  a  gene,   such  that   both   alleles   are   phenotypically   expressed   in  heterozygous  individuals

  Many  traits   are   influenced   by  several   genes

 Polygenic   inheritance -  a  pattern   of  inheritance   in  which   the  interactions   of  two   or  more   functionally   similar   genes   determine  phenotype

 Single   genes   typically  have   multiple   effects   on  phenotype

 Pleitropy -  a  situation   in  which   a  single   gene   influences   more   than one   phonotypical   characteristic

 Environmental   influences   the   expression   of  genes

 Both  heredity   and   environment   play  major   roles   in  the  development   of  various   mental   abilities

 Pedigree -  a  diagram   showing   genetic   relationships   among   a  set of  individuals,   normally   concerning  a  specific   genetic   trait

  Some  human   genetic   disorders   are   caused   by  recessive   alleles

 Carrier -  an  individual   who  is  heterozygous   for  a  recessive  condition:   displays   the   dominant   phenotype   but   can   pass   on  the  recessive   allele   to  offsprings

Albinism   results   from   a  defect   in  melanin   production

 Sickle-cell  anemia   is  caused   by  a  defective   allele   for  hemoglobin  synthesis

 Sickle-cell   Anemia -  a recessive disease caused by a single amino acid substitution in the hemoglobin molecule.

 Sickle-cell hemoglobin   molecules   tend   to  cluster   together   distorting   the  shape   of  red   blood   cells  shape   and   causing   them   to  break   and   clog capillaries

 Some  human   genetic   disorders   are   caused   by  dominant   alleles

 Some  human   genetic   disorders   are   sex-linked

 Hemophilia -  a  recessive,   sex-linked   disease   in  which   the   blood  fails   to  clot   normally

 Nondisjunction -  an  error   in  meiosis   in  which   chromosomes   fail  to segregate   properly   into   daughter   cells

 Some  genetic   disorders   are   caused   by  abnormal   numbers   of  sex chromosomes

 Turner   syndrome   (XO)-  a  sex    characteristic  typical   of  a woman   with  only  one  X  chromosome:   sterile,   tendency   to  be  very short, and   to  lack  normal   female   secondary   sexual   characteristics

 Trisomy   X-  a  condition   of  females   who  have   three   X chromosomes   instead   of  the   normal   two  X  chromosomes;   most  such   women   are   phenotypically  normal   and   fertile

  Klinefelter   syndrome   (XXY)-  a  set  of  characteristics   typically found   in  individuals   who  have   two  X  chromosomes   and   one  Y chromosome;   these   individuals   are   phenotypically   male   but   are  sterile   and   have   several   female-like  traits   including   broad   hips  and   partial   breast   development

 XYY males -  have  high  levels  of  testosterone,   severe   acne,   tall (typically   over     six  foot),  some   have   slightly   lower   IQ,  and   could  be   genetically   predisposed   to  violence

 Some  genetic   disorders   are   caused   by  abnormal   numbers   of autosomes

 Trisomy   21  =  down  syndrome