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EMBRYO SQ 17-18.docx

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BIOL 303
Dragana Miskovic

Study Questions Lectures 17-18 Aaron 1. Define environmental and chromosomal sex determinations. (When is sex determined in each of them?) L17 S3,5 a. Environmental sex determination i. Sex determined AFTER fertilization ii. Factors = temperature, location (position of embryo), stress b. Chromosomal Sex determination i. Determined at fertilization ii. Genotypic sex determination iii. Sex chromosomes 1. XY = human, mammal, drosophila 2. X-Y-XY – organism w/ alternating generation 3. ZZ ZW – bird, snake 4. XO – insects iv. Development of gonads (Primary) mostly through XY chromosomes v. Secondary Sex Characteristics w/ hormones by gonads (Secondary) 2. What is aromatase? What is the role of aromatase in sex determination? Give examples. S7 a. Aromatase – enzyme that converts the androgen testosterone into estrogen which is the rate limiting step in estrogen biosynthesis i. Correlated with environmental sex determination by temperature 1. low aromatase yields male offspring (testosterone not converted to estrogen) 2. Some species have temperature sensitive aromatase ii. Made in brain, gonads 3. What is the difference between mammalian and bird sex determination? (What is the similarity?) S3,5,13, P518 Difference Similarity Mammal Bird Sex Chromosomes Both sexes have XX (female), XY (male) ZZ (Male), ZW(Female) 1 sex -sex chromosome chromosome in autosomal in mammal common (X, Z) Male Determination Sry gene Dmrt1 gene 1 Study Questions Lectures 17-18 Aaron 4. List and briefly explain 2 female and two male sex chromosome abnormalities. S14 Male Klinefelter Syndrome Inherit 1+ X = XX+Y = tall, sterile, feminine body, may not show symptoms if ratio of XY: XXY low XYY Syndrome Inherit extra Y = XYY = high testosterone, tall, acne, fertile Female Turner Syndrome Inherit only 1 X = X0 = sterile, mental Metafemale Inherit extra X = XXX+ = fertile, tall, mental 5. Define primary and secondary sex determination in mammals. S17, P512 a. Primary sex determination = determination of gonads i. Only chromosomal, no environmental 1. Y always makes male a. Carries SRY gene that encodes testis-determining factor ii. Development of egg vs sperm b. Secondary sex determination – sexual phenotype development outside gonads through hormones i. External genitalia ii. Duct system (Wolffian vs Mullerian) 6. Where do the mammalian genitalia originate? (Remember there are two “places” of origin, one for external and one for internal genitalia). S18 a. External Genitalia – genital tubercle and urogenital sinus i. Male – Penis, Prostate, Scrotum ii. Female – labia, clitoris, lower vagina b. Internal Genitalia – potential genital ducts i. Male – Wolffian Duct – epididymis, vas deferens, seminal vesicle ii. Female – Mullerian Duct – uterus, oviduct, cervix, upper vagina 7. From what part of what germ layer do the gonads develop? Is this the same in both sexes? S19 a. Intermediate mesoderm develop into germ layer (bipotential gonads), same for both sexes 8. From what cells do the sperm and oocytes develop? Is this the same in both sexes? a. Sperm and oocytes develop from germ cells and this is the same in both sexes b. Germ cells put through different conditions to specify spermatogenesis and oogenesis 2 Study Questions Lectures 17-18 Aaron 9. Where is the gene for "maleness" located in mammals? What is this gene called (full name)? S32 a. Located in the Y chromosome on the short arm b. Sex-determing Region of the Y chromosome (SRY gene) 10. What is truly unique feature of mammalian gonads at the beginning of embryonic development and how are they called? S19 a. Bipotential Gonads are indifferent in beginning and can develop into ovaries or testes (usually gonads cannot make both) b. Unique feature of mammal gonads – go through bipotential (indifferent) stage 11. What is the origin of Sertoli and Leydig cells and what do they secrete? What are their (cells’) homologs in female gonads and what do they secrete? S22, 24 Male Female Sertoli Leydig Granulosa Cells Thecal Cells Origin Epithelial cells from Interstitial Epithelial cells Mesenchyme genital ridge mesenchyme cells of genital ridge cells of ovary Secrete Anti-mullerian factor, Testosterone estrogen androgen GDNP 12. What is the major signaling pathway responsible for the formation of testis vs. ovary from the bipotential gonad? How does this signaling work (what other proteins are involved)? S27, P530 a. Ovary i. B-catenin Pathway – Wnt4 and Rspo1 activated by genital ridge factors 1. Rspo1 further stimulate Wnt pathway > make B-catenin 2. B-catenin further activate Rspo1 and Wnt4, initiate ovarian pathway (positive feedback loop), inhibit Sox9 accumulation b. Testis i. Testis-determining pathway – genital ridge factor activate SRY gene 1. Sry activate sox9 and fgf9 2. Fgf9, repress B-catenin, prevent ovary forming pathway 3. Testis form 3 Study Questions Lectures 17-18 Aaron 13. Briefly describe the ovary pathway. S28, P517 a. Genital Ridge activate Wnt4, Rspo1 b. Wnt4 activate Wnt pathway, Rspo1 improves pathway c. Wnt pathway cause b-catenin to accumulate d. B-catenin i. induce transcription of ovary producing genes 1. activate ovary-specific transcription factors (Tatabox activating factors) ii. blocks testosterone pathway (inhibit Sox9, Sry) e. Positive loop of Wnt4/b-catenin f. Non-functional rspo1 = male development 14. Briefly describe the testis pathway. S34, P517 a. Presence of SRY gene > block b-catenin b. SRY work with Sf1 to activate sox9 c. Sox9 activate fgf9 = stimulate testis development d. Sox9 prevent b-catenin from activate ovary-producing genes e. Sox9/fgf9 loop specifies testis 15. Which protein is considered to be an autosomal testis-determining gene? What type of morphogen is it (function)? How many copies of this gene are present in the normal male cell? Could this protein be expressed from the normal (un-modified) female genome? Why or why not? What happens if XX individual has an extra copy of this gene? S34,35, P519 a. Sox9 is autosomal testis-determining gene (high mobility group box protein?) i. Transcription factor morphogen that binds to DNA to induce testis formation ii. 2 copies are present in normal male cell because autosomal iii. This protein cannot be expressed in normal female genome 1. Repressed by b-catenin, need sry and sf1 to activate sox9 iv. If XX has extra copy, will develop testis but will not have sperm development 1. Has sox9 gene expression and anti-mullerian factor 2. Seminiferous tubules lack sperm b/c 2 X chromosomes in sertoli cells 16. What is the role of Fgf9 in normal testis development? L18 S4 - Migration of mesonephric cells into XY Gonad and induction of sertoli cells 17. What is the role of SF1 in testis development? L18 S5 a. Formation of bipotential gland b. Downregulated in females, high in males c. Induce testosterone-related genes d. Regulate AMH expression (Anti-mullerian hormone) e. Convert wolffian duct to epididymis, vas deferens 4 Study Questions Lectures 17-18 Aaron 18. What is the role of Dax1 in gonadal developm
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