Human Genetics, Evolution, and Society
Human Genetics, Evolution, and Society BIOS 10101
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This 0 page Class Notes was uploaded by Dorthy Brakus on Sunday November 1, 2015. The Class Notes belongs to BIOS 10101 at University of Notre Dame taught by Harvey Bender in Fall. Since its upload, it has received 10 views. For similar materials see /class/232710/bios-10101-university-of-notre-dame in Biological Sciences at University of Notre Dame.
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Date Created: 11/01/15
Dr Bender Sex and Development Chapter 1 Central Points Fetus chromosomal sex determined at fertilization Fetal development has many stages During development a fetus becomes male or female Case A Choice of Baby s Sex Carters have three boys but always wanted a girl Interested in sex selection Varying degrees of success with several methods of sex selection available Parents request sex selection for a variety of reasons 11 How Is the Sex Determined Complex interactions between the genes and environment early in fetal development Secondary sex characteristics are not directly related to reproduction Sex chromosomes determine sex in humans In addition to 22 pairs of autosomes Females XX Males XY The Human Chromosome Set quot3 l 1 1 r u a in II M I H 1 I I M 12 I I 17 1B in 9 21 22 H u 1 i it 1 it if it it n n 6 7 8 9 10 11 12 N If 395 3 H H H 13 14 15 16 17 13 i n I i 5 19 20 X Y 31 22 sex chromosomes b Equa numbers of X and Ybearing sperm are produced Sex ratio proportion of males to females expect 11 At birth about 1105 Between ages 20 and 25 ratio is close to 11 Ratio decreases with age X and Y Chromosomes in Sex Determination Diploid germ l Diploid germ cells in female cells in male parent parent 5 Sperm gtlt X i1 3939 Ian W Meiosis gamete formation in both female and male Fertilization Sex chromosome combinations possible in new individual 8 Brooksa Cole Cengege Learning 1 5quotxwvf gt v 39 39 KILL 3 K quotT 415 i i T H iriii a gzi f Uii ii 3421 i334 ei u 32 at iii Scientific procedures for sex selection Sperm sorting Preimplantation genetic diagnosis PGD Sperm Sorting Sperm are separated from surrounding uids using a centrifuge Brookeruie Cengage Learning Sperm are then piaced in a saline solution containing a ourescent dye which binds to the DNA inthe sperm i 4 i 3 As the sperm pass one by one through a detector a bar bounces light of the dyed DNA Because Xbearing sperm have more DNA and re ect more light than Ybearing sperm each can be separated into different test tubes Sperm Sorting Sperm sorted by laser based on how brightly they fluoresce Sperm placed in uterus or eggs fertilized in a dish 4000 6000 more if eggs must be collected Success rate 90 for female births 73 for male births Acceptable method for some situations Preparation for Preim plantation Genetic Diagnosis PGD Woman given hormone treatments Multiple eggs surgically removed Eggs placed in a dish with sperm until the eggs are fertilized by in vitro fertilization IVF Embryos develop to the eightcell stage then PGD is performed Preimplantation Genetic Diagnosis 1 Process of PGD Single cell removed from each embryo Chromosomes analyzed to determine the sex Embryos of the desired sex placed into the mother s uterus Unused embryos discarded or frozen for later use or donation to others Preimplantation Genetic Diagnosis 2 More invasive procedure increased risk for mother I 12000 15000 Success rate 100 Embryos created in PGD raise many social and ethical issues Preimplantation Genetic Diagnosis PGD Eightcell embryos Single cells Embryos XX Transfer of selected embryos to patient Removal of single cell for sex chromosome f XV analysis 39 gt XY XX XX 0 Eggs are removed from Single cells are Embryos of n The selected embryos are the ovary fertilized and grown identi ed as either the desired sex are transferred to the uterus for to the eightcell stage male or female selectedr development a BrooksCale Cengage Learning 12 Development Fertilization to Birth Fusion of sperm and egg generally occurs in fallopian tube oviduct Sperm deposited in vagina move through the cervix uterus and oviduct Usually one sperm enters the egg chemical changes prevent gt one sperm Nuclei fuse to form a zygote with 46 chromosomes Stages in Human Fertilization Fallopian memion tube Sperm enter vagina Fertilization mars In the fallopian tube Szvml spzrm surrmmd the egg above but only an emu ix Th sperm nucleus luses with the egg nucleusl a A diploid zygote lumls Q Emokslcale cangaga Luming Development Embryo to Blastocyst Embryo moves to the uterus 3 4 days cell division continues Forms a large hollow ball of cells or blastocyst It contains an inner cell mass an internal cavity and an outer layer of cells Implantation in uterine wall is complete by 12 days Development The Chorion Forms Produces human chorionic gonadotropin hCG which prevents loss of uterine lining hCG in urine used for home pregnancy tests Chorion forms villi Maternal tissues and villi form the placenta Development Fertilization through Implantation Fertilization Inner cell mass DAYS 1 2 DAY 3 The DAY 4 By 96 DAY 5 The The rst cell fourcell stage hours there is blastocyst stage divisions occur a ball of lO 32 cells Brooksmole Cengaga Learning Uterine wall DAYS 6 7 The bilastocyst attaches I to the wall of the Acme uterus l w wmw 0 H 7 H A f quot 1 at rm If Er1 J Ma 91 92B H mm BmuksCule Cenqage Learning In weeks 5 and 6 the embryo grows dramatically to a length of about 11 inches 28 cm Most of the major organ systems including the heart are formed Limb buds develop into arms and legs complete with fingers and toes The head is very large relative to the rest of the body because of the rapid development of the brain By about 8 weeks the embryo is large enough to be called a fetus Although chromosomal sex XX in females and XY in males is determined at the time of fertilization the fetus appears to be neither male nor female at the beginning of the third month The sex organs cannot be seen in ultrasound scans until the 12th to 15th week All the major organs have formed and are functional By 16 weeks major changes include an increase in size and further development of organ systems Bony parts of the skeleton begin to form and the heartbeat can be heard with a stethoscope Fetal movements begin in the third month and by the fourth month the mother can feel movements of the fetus s arms and legs It has a wellformed face its eyes can open and it has fingernails and toenails Stepped Art p 13 Third Trimester Rapid growth Circulatory system and respiratory system mature Fetus doubles in size during the last eight weeks Chances for survival outside the uterus increase rapidly Case A Questions What should the Carters do Why Who should make the decision Why See textbook for further questions on this case 13 Stages of Sexual Development Formation of reproductive organs controlled by interaction between How genes function Hormones The maternal environment Sex can be defined at several levels Chromosomes Internal organs External appearance Stages of Sexual Development Structures mat wldl give rise o exmrna genitalia r 1 V chmmosnme V chromqsoma present absent 10 weeks 10 weeks Blah approaching 5th approaching a Brookscola Congage Learning Stages of Sexual Development Ap peavanc e df 39un Bmukslcule sangg Laamil g Case B Athlete Fails Sex Test Maria Patino has complete androgen insensitivity CAI or androgen insensitivity syndrome AIS Chromosomally she was a male XY MissM rs 5 name Fir r P enumial Mame 939 Martinez alde CounlryJPsya bornrive u date On the occaxlon of heA l occasmn des quld Champ iltgt r1e11 ipe A Games de Championshipe Jeux au Chempionment held atiene EH5 5 gnkrjronle 3 lhe above mentioned alhlele underwent an a the LAAF requlrernenls lor competition in Women39s athletic even 5 L39aihlete mentionne dedessus a subli un exa u et la chromative senuelle s esl rev de posmve Ceti repo xre Imenl la l urcencrsurlr aux preuves l minlnes Athlete s signature gnature de L athlete CERTIFICATENo 534l 39 quoto l hereby conli lhati icale is 77 Issued ln acco ance Wm he reportQ 39 5 Panel of the mags Je continue par la antsonle que ce certi cal est d fivre39 confirme menl an rep urt du Comin medical o icial des JeuxChamplonats mentlonr s ciconlre General ecretarv lAA F Secretair G neraI ELAA Stages of Sex Development 1 Chromosomal sex begins at fertilization Zygote has either an XX or XY Sex organs do not develop until week 7 or 8 Expression of a gene on the Y chromosome causes the gonads to become testes Sex is only one of thousands of traits Stages of Sex Development 2 Testes secrete testosterone controls development of the male reproductive organs lfY chromosome is not present the gonad develops as an ovary Female duct systems develop to form reproductive structures Male duct systems degenerate Phenotypic sex develops f m m W 171 Complete Androgen Insensitivity CAI 1 Maria Patino s disorder Mutation of androgen receptor AR gene on the X chromosome Lack receptors for testosterone or hormones derived from testosterone Cells in the gonad cannot respond to hormone Complete Androgen Insensitivity CAI 2 Female duct system and external genitals develop Individuals are chromosomal males XY Physically appear to be females with well developed breasts but limited pubic hair Do not menstruate infertile and have undescended testes in their abdomens not ovaries a BrooksiCole Cengage Learning Barr Bodies In females one X chromosome is inactivated forms Barr Body Some cells express genes from father s X chromosome some express mother s X chromosome Males and X0 individuals do not form Barr Bodies Em Q Brooksloale Cangaga Learning Sex Testing Maria Patino was XY and did not form Barr bodies Patino passed one sex test indicates the test is unreliable Other tests were used but testing caused emotional stress stigmatization and discrimination Sex testing was abolished before the 2000 Olympic Games Case B Questions ls Maria Patino a female What legal issues are important in this case See the textbook for further questions on this case 14 Legal and Ethical Issues Discrimination based on genetic conditions may occur Laws to protect discrimination based on race color sex religion or age Intersexuality Chromosomal sex of a person is not consistent with his or her phenotypic sex Or the phenotype is not classifiable as either male or female Other conditions in this category CAI Klinefelter syndrome 47XXY and Turner syndrome 45X Americans with Disabilities Act ADA Addresses the problems disabled Americans have in employment insurance and other areas This Federal act was signed into law in 1990 and protects the rights of people with disabilities Many disabilities are caused by genetic conditions Who should be covered Disability as Defined by ADA Has physical or mental impairment that substantially limits one or more major life activities or Has record or history of such impairment or Is perceived or regarded as having such an impairment Ethical and Legal Questions Question How are these questions decided Related case or legal issue Can a person be denied a job because of their sex Laws require one to hire without dis crimination Law suits are filed and decided by indi vidual judges It is difficult to determine why a person is not hired unless it is specifi cally stated a victim of discrimination Was Maria Patino The rules ofthe committee and the Olympics did not allow someone to compete as a woman if they could not pass the chromosomal test No lawsuit was filed by Maria Patino but others have forced the removal of the sex testquot rules in international ath letic competitions a Bmokleola Cengage Learning Spotlight on Law Fe v US James Frye charged with murder Took a truth test using systolic blood pressure Court did not admit testimony Scientific principle must have general acceptance in particular field to which it belongs v 1 Thank You
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