Make  a  Life  to  Save  a  Life

by

Peggy  Brickman

University  of  Georgia

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The  Case   Jack  and  Lisa  Nash’s  daughter  Molly  was  born  with  a  rare,  incurable  gene:c  condi:on  called  Fanconi  anemia,  which  rendered    her  body  unable  to  produce  enough  blood  cells…

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Matching  Organs:HLA

  Finding  a  correct  match  for  0ssue  transplanta0on  depends  on  matching  a  specific  group  of  proteins  found  on  the  surface  of  white  blood  cells  that  are  used  to  dis0nguish  one’s  own  cells  from  foreign  cells,  called  HLA,  for  human  leukocyte  an0gen.

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Learning  Objec@ves1. Recognize  how  the  number  and  type  of  

chromosomes  differ  in  a  gamete  compared  to  a  soma0c  (body)  cell.

2. Describe  how  chromosomes  are  separated  in  meiosis  and  how  this  differs  from  mitosis.

3. Apply  the  knowledge  of  how  chromosomes  separate  during  meiosis  and  the  rules  of  probability  to  predict  the  likelihood  that  offspring  from  two  parents  would  inherit  a  specific  combina0on  of  chromosomes  and  the  genes  they  contain.

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Matches  for  Organ  Dona@on

• HLA  proteins  encoded  by  several  genes  on  chromosome  6.

»Many  variants  of  gene  =  muta:ons  that  create  differences  (alleles)

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HLA  Class  IHLA  Class  IHLA  Class  IHLA  Class  IHLA  Class  IHLA  Class  IHLA  Class  I

Gene A B C E F G

Alleles 697 1,109 381 9 21 36

HLA  Class  IIHLA  Class  IIHLA  Class  IIHLA  Class  IIHLA  Class  IIHLA  Class  IIHLA  Class  II

Alleles 1,0121,0121,0121,0121,0121,012

HLA  Proteins  Present  Foreign  An5gens

6

foreign cell

Macrophage Peptides displayed by

HLA proteins

Lysosome digests proteins

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HLA: Inherited from Parents

HLA-B35HLA-A1Mrs. Nash is

diploid = twohomologuesof chromosome 6

HLA-B44HLA-A2

Review:  Mitosis

• Asexual  reproduc0on.• Occurs  in  soma0c  (body  cells)     for  growth  and  division.• Creates  gene0cally  iden0cal  cells.• Not  a  way  to  combine  traits     together  in  reproduc0on.• Need  new  method:  sexual  reproduc0on. 8

S phase

mitosis

B35A1

B44A2

Sister chromatids

B35A1

B44A2

B35A1

B44A2

Sister chromatids

B35A1

B44A2

B44A2

B35A1

Why  do  diploid  organisms  need  to  have  specialized  sex  cells?

• Sex  cells  (gametes)  allow  traits  to  be  combined  from  two  organisms.

• Can’t  just  fuse  any  two  random  cells.

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2n (46)

2n (46)+

4n = 92

too many

B35A1

B44A2

B41A3

B35A26

Sexual  Reproduc@on

• Meiosis  =  specialized  cell  division  so  you  have  only  one  of  each  chromosome,  called

• Gametes:  (n)  made  only  in  gonad  (tesMs,  ovary)

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+

2n = 46

n (23)

n (23)

B44A2

B35A26

B35A26

A2B44

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Mitosis  versus  Meiosis

Meiosis has 2 divisions: Meiosis I and Meiosis II

MITOSIS MEIOSIS

Diploid Diploid

somaticcell

gameteprecursor

duplication

Diploid Haploid

division

division

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A. 100% B35-A1B. 50% B35-B44 & 50% A1-A2C. 50% B35-A1 & 50% B44-A2D. 100% B44-A2E. 50% B35-A2, & 50% B44-A1 Mrs. Nash’s

chromosome 6s

CQ#1: When Mrs. Nash produces eggs, they would have which combinations of the HLA-A and HLA-B genes and in what proportions?

B35A1

B44A2

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Mito

sis

Meiosis I

Homologues Pair

Prophase & Metaphase Differ

B35A1

B44A2

B35A1

B44A2

Sister chromatids Sister chromatids

B35A1

B44A2

B44A2

B35A1

B35A1

B44A2

Chromosome  Pairing:  Synapsis• Close  proximity  favors  crossing  over

• Allows  exchange  of  traits

Exchange of parts of non-sister chromatidsDuplicatedMaternalchromosome

DuplicatedPaternalchromosome

sisterchromatids

non-sisterchromatids

tetrad

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Mitosis Meiosis IHomologues

Pair

B35A1

B44A2

Sister chromatids

B35A1

B44A2

Sister chromatids

meiosis Imitosis

B35A1

B44A2

B35A1

B44A2

B35A1

B35A1

B44A2

B44A2

B35A1

B44A2

B44A2

B35A1

B35A1

B44A2

Update:  Meiosis  I  completed

• Homologous  chromosomes  are  separated  into  two  different  cells.

• Each  new  cell  has  only  one  of  each  different  chromosome  (n,  haploid).

• S0ll  need  to  separate  the  sister  chroma0ds  so  that  the  total  amount  of  chromosomes  and  DNA  is  truly  half  of  a  normal  cell.

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Meiosis  II:  Sister  chroma0ds  separate

End  result:  Four  haploid  cells  total17

meiosis IImeiosis II

B35A1

B44A2

B35A1

B44A2

B35A1

B35A1

B44A2

B44A2

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A. 100% B5-A26B. 50% B35-A3 & 50% B41-A26C. 50% B35-B41 & 50% A3-A26D. 100% B44-A2 B35-A26E. 50% B35-A26, & 50% B41-A3

Mr. Nash’s chromosome 6s

CQ#2: When Mr. Nash produces sperm, the sperm would have which combinations of the HLA-A and HLA-B genes and in what proportions?

B41A3

B35A26

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A. B35, B35, A1, A2B. B35, B44, A2, A3C. B44, B35, A2, A26D. B41, B44, A26, A2

Mrs. Nash Mr. Nash

CQ#3: Which of the following shows one combination of HLA-A and HLA-B genes expected in an offspring of Lisa and Jack Nash?

B41A3

B35A26B35

A1B44A2

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A. YesB. No

Mrs. Nash Mr. Nash

CQ#4: Is it possible for any child born to this couple to be identical in both HLA-A and HLA-B with either parent?

B41A3

B35A26B35

A1B44A2

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A. No chanceB. 25%C. 50%D. 75%E. 100%

Chromosome 6s for Molly Nash

CQ#5: Using the proportion of each type of sperm and egg that you calculated in questions I and II, what is the likelihood that Molly’s sibling would inherit the same combination of HLA genes and thus be a good organ donor for Molly?

B35A26 B44

A2

  Clearly  Molly’s  best  chance  of  finding  a  bone  marrow  match  was  with  a  sibling.  Unfortunately,  Molly  was  an  only  child.  The  Nashes  had  always  wanted  to  have  more  children,  but  because  Fanconi  anemia  is  an  inherited  condi:on,  they  knew  that  if  they  had  another  child  that  child  had  a  chance  of  geJng  the  disease  just  as  Molly  had.  But  neither  Jack  nor  Lisa  had  the  disease  because  the  muta:on  is  recessive.  In  order  to  have  Fanconi  anemia  like  Molly,  both  copies  of  the  FANCC  gene  would  have  to  have  this  recessive  muta:on,  and  they  only  had  one.

               How  is  that  possible?

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Fanconi  Anemia:  Chromosome  9

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Normal FANCC

Mother

NormalFANCC

Fathermeiosismeiosis

NormalFANCCNormal FANCC

Molly

FANCC FANCC

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A. 0%B. 25%C. 50%D. 75%E. 100%

CQ#6: Using what you know about how meiosis created eggs and sperm, what is the likelihood that Lisa and Jack Nash could conceive a sibling for Molly that would NOT have Fanconi anemia (presence of at least one normal)?

PunneD  Squares:    Show  All  Possible  Combina5ons  of  Gametes

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Normal FANCC

Mother

NormalFANCC Father

NormalFANCC

meiosis

Normal

FANCC

mei

osis

FANCCnormal normalnormal

FANCCFANCC FANCCnormal

Pre-­‐Implanta5on  Gene5c  Screening

• When  they  discovered  that  they  could  conceive  a  baby  that  was  free  from  Fanconi  Anemia,  Jack  and  Lisa  Nash  underwent  in-­‐vitro  fer0liza0on  followed  by  a  procedure  called  pre-­‐implanta0on  gene0c  screening  to  choose  an  embryo  that  would  have  HLA  proteins  (B44,  B35,  A2,  A26)  that  matched  Molly,  and  to  choose  an  embryo  that  would  also  be  free  of  Fanconi  anemia.

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• Ethics:  This  is  the  first  example  of  the  use  of  pre-­‐implanta:on  gene:c  screening  to  select  for  a  baby  solely  as  a  treatment  for  its  sibling.

• List  two  ethical  objec:ons  someone  might  have  to  allowing  the  Nashes  to  use  this  technique.

• List  two  reasons  why  you  think  the  Nashes  should  be  allowed  to  use  this  technique.

•  What  kind  of  regula:ons  if  any  should  be  used  for  parents  hiring  doctors  to  do  this  procedure?    When  is  it  OK,  when  not?

Pre-Implantation Genetic Screening

Select  a  Baby:  HLA  Match,  Normal

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FatherMother

Molly

B44

A2

FANCC FANCC

B35

A26

NormalFANCC

B35 B44A1 A2

NormalFANCC

B41A3

B35A26

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A. No chanceB. 25%C. 50%D. 75%E. 100%

NormalFANCC

B35 B44A1 A2

CQ#7: Using your knowledge of how chromosomes segregate during

meiosis, what percent of Mrs. Nash’s eggs would carry a normal

chromosome 9 and a chromosome 6 with the A-2, B-44 alleles?

Alignment  at  Metaphase  I  Random:

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Meiosis IMeiosis II

Meiosis IMeiosis II

NormalFANCC

B35 B44A1 A2

Normal FANCC

B35 B44A1 A2

B35A1

B44A2

B44A2

B35A1

A1

B35

A1

B35

A2

B44

A2

B44

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A. 1/2B. 1/4C. 1/8D. 1/16E. 1/32

Father

NormalFANCC

B41A3

B35A26

CQ#8: If the same percentage of Mr. Nash’s sperm carry the correct chromosome 9 (normal) and 6 (A26, B35), what is the probability that a single embryo would be a perfect HLA match for Molly and not develop Fanconi anemia?

NormalFANCC

B35 B44A1 A2

32B35A1

B44A2

A1

B35

A2

B44

B41A3

B35A26

B35A26

B41A3

B35A26

B41A3

B41A3

B41A3

B41A3

B41A3

B41A3

B41A3

B41A3

NormalFANCC

NormalFANCC

NormalFANCC

NormalFANCC

NormalFANCC

NormalFANCC

NormalFANCC

NormalFANCC

B35A26

B35A26

B35A26

B35A26

B35A26

B35A26

B35A26

Normal Normal

FANCC FANCC

FANCC FANCC FANCC FANCC

FANCC FANCC

Normal Normal

Normal NormalNormal Normal

A2

B44

A2

B44

A2

B44

A2

B44

A2

B44

A2

B44

A2

B44

A2

B44

A1

B35A1

B35

A1

B35

A1

B35

A1

B35

A1

B35

A1

B35A1

B35

Update  on  the  NashesANer  four  in  vitro  ferMlizaMon  aOempts,  Lisa  Nash  gave  birth  to  a  baby  boy,  Adam,  on  August  29,  2000.    Adam’s  placenta  was  gathered  immediately  and  all  the  cord  blood  saved.    Molly  started  chemotherapy  to  destroy  her  bone  marrow  and  received  a  transfusion  of  the  cord  blood  cells  a  month  later.    Today  Molly,  Adam,  and  new  liOle  sister  Delaine  are  all  doing  well.    The  transplant  cured  Molly’s  bone  marrow  failure,  but  she  sMll  suffers  from  Fanconi

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anemia  and  visits the  doctors  35-­‐40 Mmes  a  year  to  screen  for  solid-­‐tumor  cancers.    A  common  cold  could  have  dire  consequences  for  her,  but  her  bone  marrow  is  funcMoning  normally.  

Slide  CreditsSlide  1    and  Slide  33    

Descrip(on:  Illustra:on  of  embryo  in  flask.  Author:  czardases  

Source:  Fotolia,  h]p://www.fotolia.com,  ID:  7576662  

Clearance:  ©czardases,  licensed  royalty  free.  

Slide  2    Descrip(on:  Clu]ering  of  red  blood  cells.  

Author:  Bram  Janssens  Source:  Dreams:me,  h]p://www.dreams:me.com,  ID:  6767785  

Clearance:  ©Bram  Janssens,  licensed  royalty  free.  

Slide  3    

Descrip(on:  Illustra:on  of  MHC  class  I  and  class  II.  Author:  David  S.  Goodsell  and  the  RCSB  PDB  

Source:  Major  Histocompa:bility  Complex,  Molecule  of  the  Month,  February  2005,  h]p://www.pdb.org  Clearance:  Molecule  of  the  Month  illustra:ons  are  copyrighted  but  available  for  educa:onal  purposes,  

provided  a]ribu:on  is  given  to  David  S.  Goodsell  and  the  RCSB  PDB.  

Slide  5  —Bo]om  lel  

Descrip(on:  Drawing  depic:ng  HLA  genes  on  chromosome  6.  Author:  Philip  Dei:ker  

Source:  Wikimedia  Commons,  h]p://commons.wikimedia.org/wiki/Image:HLA.jpg  

Clearance:  Released  into  the  public  domain  by  the  author.  

Slide  9    and  Slide  10    Descrip(on:  Figure  of  male  and  female.  

Author:  Derived  from  a  public  domain  NASA  image.  Source:  WikiMedia,  h]p://commons.wikimedia.org/wiki/File:Human.svg  

Clearance:  Public  domain.

All  remaining  images  appearing  in  this  presenta(on  were  created  by  the  author  of  this  case  study,  Peggy  Brickman.