Make a Life to Save a Life by

Make a Life to Save a Life by Peggy Brickman University of Georgia 1

The Case Jack and Lisa Nash’s daughter Molly was born with a rare, incurable genetic condition called Fanconi anemia, which rendered her body unable to produce enough blood cells… 2

Matching Organs: HLA Finding a correct match for tissue transplantation depends on matching a specific group of proteins found on the surface of white blood cells that are used to distinguish one’s own cells from foreign cells, called HLA, for human leukocyte antigen. 3

Learning Objectives 1. Recognize how the number and type of chromosomes differ in a gamete compared to a somatic (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 combination of chromosomes and the genes they contain. 4

Matches for Organ Donation • HLA proteins encoded by several genes on chromosome 6. » Many variants of gene = mutations that create differences (alleles) HLA Class I Gene A Alleles B C 697 1, 109 381 E F G 9 21 36 HLA Class II 6 Alleles 1, 012 5

HLA Proteins Present Foreign Antigens foreign cell Macrophage Lysosome digests proteins Peptides displayed by HLA proteins 6

HLA: Inherited from Parents Mrs. Nash is diploid = two homologues of chromosome 6 HLA-A 1 HLA-B 35 HLA-A 2 HLA-B 44 7

A 1 B 35 Review: Mitosis A 2 B 44 S phase • Asexual reproduction. Sister chromatids • Occurs in somatic (body cells) A 1 B 35 for growth and division. • Creates genetically identical cells. A 2 B 44 • Not a way to combine traits mitosis together in reproduction. • Need new method: sexual A 1 A 2 B 35 B 44 reproduction. 8

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. A 1 B 35 A 2 B 44 2 n (46) + 2 n (46) A 3 B 41 A 26 B 35 4 n = 92 too many 9

Sexual Reproduction • Meiosis = specialized cell division so you have only one of each chromosome, called • Gametes: (n) made only in gonad (testis, ovary) A 2 B 44 n (23) + 2 n = 46 n (23) A 2 B 44 A 26 B 35 10

Mitosis versus Meiosis MITOSIS MEIOSIS Diploid somatic cell Diploid gamete precursor duplication division Diploid Haploid division Meiosis has 2 divisions: Meiosis I and Meiosis II 11

CQ#1: When Mrs. Nash produces eggs, they would have which combinations of the HLA-A and HLA-B genes and in what proportions? A. 100% B 35 -A 1 B. 50% B 35 -B 44 & 50% A 1 -A 2 C. 50% B 35 -A 1 & 50% B 44 -A 2 D. 100% B 44 -A 2 E. 50% B 35 -A 2, & 50% B 44 -A 1 B 35 A 2 B 44 Mrs. Nash’s chromosome 6 s 12

A 2 A 1 A 2 B 35 B 44 Sister chromatids A 1 B 35 A 2 B 44 Sister chromatids Homologues Pair A 1 B 35 Meiosis I Mitosis A 1 A 2 B 44 Prophase & Metaphase Differ 13

Chromosome Pairing: Synapsis • Close proximity favors crossing over Exchange of parts of non-sister chromatids Duplicated Maternal Paternal chromosome tetrad • Allows exchange of traits sister chromatids non-sister chromatids 14

A 1 B 35 Mitosis A 2 B 44 A 1 B 35 Meiosis I Sister chromatids A 1 B 35 A 2 B 44 Homologues Pair mitosis A 1 B 35 A 2 B 44 Sister chromatids A 1 B 35 A 2 B 44 meiosis I A 1 B 35 A 2 B 44 15

Update: Meiosis I completed • Homologous chromosomes are separated into two different cells. • Each new cell has only one of each different chromosome (n, haploid). • Still need to separate the sister chromatids so that the total amount of chromosomes and DNA is truly half of a normal cell. 16

Meiosis II: Sister chromatids separate A 1 B 35 A 2 B 44 meiosis II A 1 B 35 A 2 B 44 End result: Four haploid cells total 17

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? A. 100% B 5 -A 26 B. 50% B 35 -A 3 & 50% B 41 -A 26 C. 50% B 35 -B 41 & 50% A 3 -A 26 D. 100% B 44 -A 2 B 35 -A 26 E. 50% B 35 -A 26, & 50% B 41 -A 3 B 41 A 26 B 35 Mr. Nash’s chromosome 6 s 18

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? A. B 35, A 1, A 2 B. B 35, B 44, A 2, A 3 C. B 44, B 35, A 26 D. B 41, B 44, A 26, A 2 A 1 B 35 A 2 B 44 Mrs. Nash A 3 B 41 A 26 B 35 Mr. Nash 19

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? A. Yes B. No A 1 B 35 A 2 B 44 Mrs. Nash A 3 B 41 A 26 B 35 Mr. Nash 20

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? A. No chance B. 25% C. 50% D. 75% E. 100% A 26 B 35 A 2 B 44 Chromosome 6 s for Molly Nash 21

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 condition, they knew that if they had another child that child had a chance of getting the disease just as Molly had. But neither Jack nor Lisa had the disease because the mutation is recessive. In order to have Fanconi anemia like Molly, both copies of the FANCC gene would have to have this recessive mutation, and they only had one. How is that possible? 22

Fanconi Anemia: Chromosome 9 Normal FANCC Father meiosis Mother meiosis Normal FANCC Normal FANCC Molly 23

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)? A. 0% B. 25% C. 50% D. 75% E. 100% 24

Punnett Squares: Show All Possible Combinations of Gametes FANCC Normal Father meiosis Normal FANCC Mother meiosis FANCC Normal normal FANCC normal FANCC Normal FANCC 25

Pre-Implantation Genetic Screening • When they discovered that they could conceive a baby that was free from Fanconi Anemia, Jack and Lisa Nash underwent in-vitro fertilization followed by a procedure called pre -implantation genetic screening to choose an embryo that would have HLA proteins (B 44, B 35, A 26) that matched Molly, and to choose an embryo that would also be free of Fanconi anemia. 26

Pre-Implantation Genetic Screening • Ethics: This is the first example of the use of preimplantation genetic screening to select for a baby solely as a treatment for its sibling. • List two ethical objections 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 regulations if any should be used for parents hiring doctors to do this procedure? When is it OK, when not? 27

Select a Baby: HLA Match, Normal A 1 B 35 FANCC A 2 A 3 A 26 B 44 B 41 B 35 FANCC Normal Mother A 26 B 44 B 35 FANCC Normal Father FANCC Molly 28

CQ#7: Using your knowledge of how A 1 chromosomes segregate during B 35 meiosis, what percent of Mrs. Nash’s eggs would carry a normal FANCC chromosome 9 and a chromosome 6 with the A-2, B-44 alleles? A 2 B 44 Normal A. No chance B. 25% C. 50% D. 75% E. 100% 29

Alignment at Metaphase I Random: A 1 B 35 FANCC A 2 A 1 B 44 B 35 Normal Meiosis II A 2 B 44 FANCC Meiosis II A 1 A 1 A 2 A 2 B 35 B 44 30

CQ#8: If the same percentage of Mr. Nash’s sperm carry the correct chromosome 9 (normal) and 6 (A 26, B 35), what is the probability that a single embryo would be a perfect HLA match for Molly and not develop Fanconi anemia? A. 1/2 B. 1/4 C. 3/16 D. 1/8 E. 1/16 A 1 B 35 FANCC A 2 A 3 A 26 B 44 B 41 B 35 Normal FANCC Normal Father 31

A 2 B 44 A 1 B 35 A 26 A 3 B 41 B 35 B 41 A 3 A 2 B 41 B 44 FANCC A 26 A 2 B 35 B 44 FANCC A 26 A 2 A 3 A 2 B 35 B 44 B 41 B 44 Normal. FANCC Normal A 3 A 1 A 26 A 1 A 3 A 1 B 41 B 35 B 35 B 41 B 35 FANCC Normal. FANCC A 3 A 26 B 41 B 44 B 35 B 44 FANCC A 1 A 3 Normal A 2 B 44 Normal A 26 A 2 A 3 B 35 B 44 Normal. FANCC Normal B 41 Normal A 2 B 44 Normal A 3 A 1 A 26 A 1 A 3 A 1 B 41 B 35 B 35 B 41 B 35 FANCCFANCC Normal FANCC 32 Normal

Update on the Nashes After four in vitro fertilization attempts, 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 little sister Delaine are all doing well. The transplant cured Molly’s bone marrow failure, but she still suffers from Fanconi anemia and visits the doctors 35 -40 times a year to screen for solidtumor cancers. A common cold could have dire consequences for her, but her bone marrow is functioning normally. 33

Slide Credits Slide 1 and Slide 33 Description: Illustration of embryo in flask. Author: czardases Source: Fotolia, http: //www. fotolia. com, ID: 7576662 Clearance: ©czardases, licensed royalty free. Slide 2 Description: Cluttering of red blood cells. Author: Bram Janssens Source: Dreamstime, http: //www. dreamstime. com, ID: 6767785 Clearance: ©Bram Janssens, licensed royalty free. Slide 3 Description: Illustration of MHC class I and class II. Author: David S. Goodsell and the RCSB PDB Source: Major Histocompatibility Complex, Molecule of the Month, February 2005, http: //www. pdb. org/pdb/static. do? p=education_discussion/molecule_of_the_month/pdb 62_2. h tml Clearance: Molecule of the Month illustrations are copyrighted but available for educational purposes, provided attribution is given to David S. Goodsell and the RCSB PDB.

Slide 5 —Bottom left Description: Drawing depicting HLA genes on chromosome 6. Author: Philip Deitiker Source: Wikimedia Commons, http: //commons. wikimedia. org/wiki/Image: HLA. jpg Clearance: Released into the public domain by the author. Slide 9 and Slide 10 Description: Figure of male and female. Author: Derived from a public domain NASA image. Source: Wiki. Media, http: //commons. wikimedia. org/wiki/File: Human. svg Clearance: Public domain. All remaining images appearing in this presentation were created by the author of this case study, Peggy Brickman.