Presentation on theme: "Sex for the purposes of this class refers to 4 components"— Presentation transcript:
1Sex for the purposes of this class refers to 4 components Gonadal sexGonads or where gametes are produced by meiosisSomatic sexSomatic cells are cells that undergo mitosis.They can be divided into primary and secondary characteristicsSecondary somatic sex characteristics are divided further into hair and bodySexual identificationSexual orientation
2FOR HUMAN MALES Gonadal sex Consists of the testes where the gametes or sperm are producedSomatic sex characteristicsPrimary and SecondaryMale primary somatic sex characteristicspenis and scrotumMale secondary somatic sex characteristicsHairfacial hair chest hair body hairBodypelvic build straight hipsmuscular build upper bodyAbility to generate muscle mass at a faster rate than females following puberty
3FOR HUMAN FEMALES Gonadal sex Ovaries where eggs are produced Female primary somatic sex characteristicsClitoris, labia, vagina, cervix, uterus, fallopian tubes, and the ability to bear childrenFemale secondary somatic sex characteristicsHair vellus rather than terminal hairBodyrounded hips, breasts, ability to nurse offspring, menstrual cycle, increased body fat composition, decreased upper body strength, decreased ability to generate muscle mass at a fast rate
5Sex chromosomes determine gender Human males are the heterogametic sex with two different sex chromosomes, (XY).Human females are the homogametic sex (XX).In other species sex determination differs:male birds ZZfemale birds ZW
6Sexual development At the beginning of human development either male orfemale development ispossible.Unspecialized gonads andtwo sets of reproductiveducts exist until 6th week of development.An embryo develops as amale or female usinginformation from the Ychromosome.
7Genes on the Y chromosome Y chromosome first seen 1923Tips of Y chromosome are pseudoautosomal regions PAR1 and PAR2They make up 5% of the chromosomeContain 63 pseudoautosomal genes that cross over with the X chromosomeMost of the Y is male specific region or MSY
8Genes on the Y Chromosome Y chromosome has 2 pseudoautosomal regions whose genes match genes on the X chromosomeAnd a large central region that does not recombine with the X chromosomeThis non-recombining region makes up about 95% of the chromosome
93 Classes of Genes on the Y Genes shared with X chromosome define the pseudoautosomal regions (PAR)Genes similar to X chromosome genes are X-Y homologsGenes unique to the Y including SRY gene
10Genes on the Y chromosome Y chromosome is small and gene poor and prone to deletionSince the Y can not recombine with X, its genes began to rotGenes decayed except for SRY and the tipsThe Y is degrading fast, losing genes at the rate of 5/million yearsMay have a way out of complete degredationMany of the DNA segments are palindromes
12During male meiosis a synaptonemal complex forms and one chiasma will always form in this region This results in regular exchange of material between the tips of XP and YPAny genes in this region are inherited as thought they are autosomal and that is why it is called the pseudoautosomal region PARContains known genes including the RSP gene for making ribosomes
14SEX REVERSALThis mutant hybrid chromosome is called an X (TDF) chromosomeWhen it fertilizes an X bearing egg it results in a 46 XX (TDF) maleWhen the corresponding mutant y chromosome fertilizes an egg it results in a 46 XY female
15SEX REVERSALKaryotype is XX but this individual will develop as an XY male because of the presence of the testes determining factor geneRemember the presence of testes, determines gonadal sex in malesEven though these individual will look male they will suffer from testicular atrophy or small testes and sterilityWhat causes the sterility?
16SEX REVERSALIn humans if there are 2 X chromosomes in a male germ line , it acts as a poison to the germ cells and kills them during meiosisThe gonadal sex of this individual will be male because they will have testesBut they can not make viable sperm
17SEX REVERSALWhen a sperm carrying a Y (delTDF) chromosome fertilizes an X bearing egg the result is anXY(delTDF) zygoteThis individual develops as female even though the karyotype is XYOvaries are reduced and eggs that are produced will not surviveHave a female build but little pubic or underarm hair
21Mutations in genes involved in sexual development affect gender Mutation/absence of:SRY gene Normal female developmentAnti-Mullerian hormone Mullerian ducts persist in malegeneTestosterone gene Early development as femaleMasculinization at pubertyDHT converting enzyme External structures lack signaland develop as female,internal structures are male.
22HORMONES Travel in the blood stream to receptors on the target cell Receptors bind the hormone and carry it across the plasma membrane of the cell to the nucleusOnce inside the nucleus the hormone binds to DNA to promote gene expressionIt is the protein products of these genes that lead to sexual differentiation
23HORMONESChemical messengers that are produced by one cell type, released into the bloodstream and received by the target cellHormones regulate gene expression in the target cellWe will look at:testosteroneexcreted by testes and adrenal cortex in malesestrogenexcreted by ovaries and adrenal cortex in females
24HORMONE RECEPTORS AND GENE REGULATION The TDF gene is on the Y chromosome and codes for the development of testes which produce testosteroneBut the receptor for testosterone is regulated by a gene on the X chromosomeThis AR gene or androgen receptor gene codes for the testosterone receptorA mutation in this gene cause testicular feminizationIndividuals are XY with a normal Y chromosome with a normal TDF gene
25HORMONE RECEPTORS AND GENE REGULATION They can not respond to testosterone’s masculinizing effects because they have no receptors to transport testosterone across the cell membraneAffected individuals develop as phenotypic females who are sterileThis mutation is known as the AIS mutation, androgen insensitivity syndrome
26ANDROGEN INSENSITIVITY SYNDROME Produce testosteroneThis is where they differ from the XY (TDF del) individualsThey have no receptors to transport testosterone across the cell membraneReferred to as AIS femalesOccur 1/20,000 birthsTaller than averageExternal genitals are femaleVagina looks normal from the outsideNewborn is declared a girl and raised as such
27ANDROGEN INSENSITIVITY SYNDROME In utero AIS females develop testes because TDF gene present so their gonadal sex is maleProduce MIF and Mullerian ducts regressBut the cells of the embryo cannot sense testosteroneInstead they respond to the low levels of estrogen being produced by the adrenal cortex and develop as femaleAt birth appear femaleNo vagina, cervix, uterus or fallopian tube
283 WAYS TO MANIFEST TESTICULAR FEMINIZATION XY (TDF del)no testosteroneXY point mutation of TDF geneXY with normal Y but with AIS mutation so no receptors for testosteroneAll these individuals will be tall
29SEX DETERMINATION IN HUMANS REQUIRES 4 ELEMENTS TO BECOME MALE Y chromosome intact TDF gene (no point mutations)Sensing mechanism in the indifferent gonad to the testes determining factorTestosterone or estrogen produced by the gonadsTestosterone or estrogen receptors in the somatic tissues intact. No AIS (androgen insensitivity syndrome)
31Born XY with female genitalia GUEVEDOCESBorn XY with female genitaliaAt puberty the adrenal gland begins to produce testosteroneCauses masculinizationvoice deepensmuscles developno breast development and no mensesadrenal testosterone causes clitoris to enlarge and resemble a penis
32SEX CHROMOSOME ANEUPLOIDY Aneuploidy refers to an abnormal number of chromosomesSuch anomolies occur often enough that they have been recognized and studied by medical scienceWe will discuss 3 different cases of aneuploidyKlinefelter males XXYXYYTurner syndrome XO
33Nondisjunction in Sex Chromosomes XXXXXYKlinefelter syndromeXOTurner Syndrome
34What determines gender? Number of X chromosomes, orpresence of Y chromosome?Individuals with unusual chromosomecombinations provide a clue:X0XXYXY femalesXX malesFemale with Turner syndromeMale with Klinefelter syndromeSRY gene missingSmall bit of Y with SRY gene present=> Y chromosome determines gender.=> SRY gene on Y chromosome determines gender.
35KLINEFELTERKlinefelter males have an extra X chromosome so they karyotype as XXY malesOccurs 1/1000 live births1940 Harry Klinefelter at Massachusetts General Hospital described a syndrome occurring in males not usually detected until after puberty
36The testes are atrophied and do not produce much testosterone KLINEFELTERThe testes are atrophied and do not produce much testosteroneThe level may be so low as to be about the same amount as the estrogen produced by the adrenal cortexBecause the level is so low during puberty these individuals do not undergo normal development of male secondary sex characteristics, including muscular upper body, narrow hips and chest and facial hair
37Remain sterile because the undeveloped testes can not produce sperm KLINEFELTERIf treated during puberty with testosterone then breast development will stop and the hips will narrow and become more male likeThey will develop muscular upper bodies, broad shoulders, square jaw and deep voicesRemain sterile because the undeveloped testes can not produce spermBut outwardly they will look like normal males
38They found 7 of those males had a 47 XYY karyotype XYY MALES1965 Jacobs in Scotland looked at the chromosomes of 197 mentally subnormal males with violent tendenciesThey found 7 of those males had a 47 XYY karyotype7/197 = 1/28 a much higher ratio than among other groups of males testedXYY occurs 1/1000 live birthsAmong tall males about 1/325Among tall penal inmates 1/30
39XYY males are over represented in mental and penal institutions Large scale study done by the Danish government suggested that tall males with lower intellectual function are more likely to be convicted of crimes regardless of their karyotypeXYY karyotype is over represented in tall males 1/325More than 95% of all XYY males are not in prison