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Notes based on PowerPoint 15

by: Bennett Notetaker

Notes based on PowerPoint 15 Bio 130, 15017

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Discusses sex differentiation
BIO130LEC000:Perspectives in Human Bio
James Lafountain
Class Notes
sex, Chromosomes
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This 5 page Class Notes was uploaded by Bennett Notetaker on Thursday April 21, 2016. The Class Notes belongs to Bio 130, 15017 at University at Buffalo taught by James Lafountain in Spring 2016. Since its upload, it has received 24 views.


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Date Created: 04/21/16
Bio 130 Block 4: PowerPoint 15 04/21/2016 ▯ MRI:  Body is surrounded in a core by powerful electromagnets  Strong field of magnets causes alignment of hydrogen atoms  When ‘on’ alignment is displaced  When ‘off’ realignment  Realignment gives off a signal that can be converted to an image by a computer using an algorithm ▯ Human Development and Sex Determination:  Phenotypic sex is generally determined by the sex chromosome content of the karyotype  Exceptions are evident in cases where X-Y translocation occurs or where sex hormone receptors are defective ▯ Range of Sex Chromosome Combinations in Humans:  Only having one sex chromosome o 45,X: Turner’s syndrome female o 45,Y: lethal  Having two sex chromosomes o 46,XX: female o 46,XY: male  At least one X is needed and a Y with an X yields male phenotype ▯ During Embryogenesis: (pictures on PowerPoint) Sex determination is at fertilization based on genotype of embryo Sex differentiation is evident at about week 8 based on development of external genitalia (phenotypic sex) Differentiation of internal sex organs (gonadal differentiation) is subject to hormonal control but is normally complete at time of birth ▯ Sex Differentiation begins in the Embryo:  Undifferentiated duct systems are established  In 46,XX females, the absence of a Y chromosome allows the indifferent Mullerian ducts to develop  In 46,XY males the SRY gene on the Y chromosome causes the indifferent Wolffian system to develop testes and the X chromosome produces necessary androgen receptors ▯ SRY (Sex-determining region Y):  Sex-determining gene on the Y chromosome in the therians  Gene encodes a transcription factor (DNA binding protein)  Protein is called testis determining factor (TDF), which initiates male sex differentiation  Mutations in this gene give rise to XY females with gonadal dysgenesis (Swyer syndrome) o Gonadal Dysgenesis-  Essentially the phenotype seen with Turner’s syndrome (45,X) in (46,XY) with mutant SRY  No ovarian development, fibrous masses  Without AMH, the other elements of Mullerian ducts develop (fallopian tubes, cervix, uterus, vagina)  Immature female phenotype at puberty, due to absence of hormones  Infertility  Translocation of part of the Y chromosome containing this gene to the X chromosome causes XX male syndrome ▯ Two pathways to sex differentiation:  Default pathway leads to femaleness, possible with just one X chromosome two X required for fertility, Mullerian ducts develop in (46,Xx)  SRY-directed pathway to maleness, dependent on a Y chromosome, X chromosome needed for x-linked genes, particularly androgen receptor, Wolffian ducts develop in (46,XY) ▯ Hormones play important roles in sex differentiation:  Testosterone is a potent androgen that is secreted by Leydig cells of the developing testes and it acts to develop pre-genitalia and pre- reproductive tract cells of embryonic males  Anti-Mullerian hormone is secreted by Sertoli cells of the embryonic testes  AMH targets Mullerian ducts, causing degeneration as male development proceeds o Testis structure reviewed:  Seminiferous tubules are sperm generating ducts many meters long  Space between tubules contains interstitial cells  Leydig cells are a major type of interstitial cell that secretes androgen hormones o Within seminiferous tubules:  Spermatocytes, spermatids are supported by Sertoli cells which function to supply nutrients  Sertoli cells in embryonic testes secrete AMH ▯ AMH targets Mullerian ducts, causing degenerations of Mullerian ducts as male development proceeds:  Anti-Mullerian hormone is secreted by the Sertoli cells of the embryonic testes: action of AMH is on Mullerina ducts, causing them to degenerate ▯ Androgens secreted by embryonic testes are steroid hormones:  Secreted by Leydig cells (interstitial, non-germ line cells) of embryonic testis  Diffuse throughout the embryo  When reach target cells, androgens enter the cytosol and are bound by hormone receptor  Hormone/receptor complexes diffuse into nucleus  Target cell-specific genes are activated ▯ Leydig Cells:  Interstitial cells between seminiferous tubules  Steroid hormones (androgens) are secreted from Leydig cells into entire embryo ▯ Mechanism of action: steroid hormones:  Hormones enters target cell from extracellular space  Mechanism of entry is diffusion across plasma membrane  Binding to inactive receptor occurs in cytosol  Activated receptor and bound hormone diffuse into nucleus  Hormone/receptor complex binds to target genes o Notable steroid hormones:  Estradiol- released from ovary in promoting secondary sex features  Testosterone- released from testes in promoting virilizing effects in males  Aldosterone- released form adrenal cortex in regulating blood volume  Cortisol- released from adrenal cortex in regulating sugar metabolism  Progesterone- from ovary to regulate cervical mucus o Steroid Hormones:  Are synthesized from cholesterol  They are lipids  Steroid hormones are both water soluble  Properties allow them to pass through a cell’s membrane ▯ AMH is a peptide hormone:  Secreted by Sertoli cells (non-germ line cells) of embryonic seminiferous tubules  AMH diffuses throughout embryo  Binds to AMH-ll receptors in cell membranes of Mullerian ductwork  Binding initiates a signal cascade  Outcome is programmed cell death (apoptosis) of Mullerian ductwork cells ▯ More on Sertoli cells:  Cells within seminiferous tubules, adjacent to germ-line cells  A kind of “nurse cell” that support germ-line cells  Secretory cells, based on endoplasmic reticulum-Golgi- secretory vesicle pathway  AMH is a peptide hormone secreted by Sertoli cells ▯ Mechanism of action: Peptide hormones:  Hormone binds to receptor on cell surface  Receptor is activated and facilitates activation of ‘first-line’ effectors  Second-line effectors are activated  Signal cascade results in activation of transcription factors that activate target cell genes o Notable peptide hormones:  Growth hormone from anterior pituitary acts on muscle, bone  ACTH from anterior pituitary acts on adrenal gland  Prolaction from anterior pituitary acts on mammary glands  Leutinizing hormones form anterior pituitary on ovary/ovulation ▯ In females lacking Y:  Default mechanism prevails  Wolffian ducts degenerate in the absence of androgen  Mullerian ducts develop ▯ In males possessing Y chromosome:  If androgen hormone receptor present in target tissues, then male development  If androgen hormone receptor is defective or absent in target tissues, then default female development ▯ Androgen Receptors:  A large cytosolic protein- 910 amino acids  Gene locus is on X chromosome  Each receptor consists of a portion that binds the androgen and a portion that binds to DNA in steroid-sensitive areas of nuclear chromatin, that control transcription of male-related genes  Androgen is bound to receptor in cytosol and then moves into the nucleus for its action on male-related genes  Androgen “activates” it’s receptor for binding to maleness-related genes in the nucleus  Specific binding to maleness-related gene promotes  Causes chromatin remodeling in such genes  Active receptor acts as a transcription factor in regulating gene expression ▯ Where in the embryo is this occurring:  Within cells of the Wolffian duct system  Wolffian ducts develop into male reproductive tract: testes, vas deferens, epididymis, prostate  Within cells of indifferent genitalia to cause male genitalia to form ▯ This does not happen in cells of the Mullerian ducts:  In the embryo, androgen receptors are specifically in cells of Wolffian ducts  Androgens may diffuse into degenerating Mullerian cells, but have no effect in absence of receptors ▯ ▯


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