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Sex differentiation
Determination, clinical diseases
| Term | Definition |
|---|---|
| What does meiosis do? | Generates haploid gametes, sets up gametes for fertilisation, produces new genetic combinations |
| What is the process of meiosis? | M1 -> homologous chr pair up to form tetrads -> programmed induction of ds breaks -> rearrangement of genetic info sequences in each chr (chiasmata) -> haploid gametes, M2 -> chromatid separation |
| What is syngamy? | Coming together of 2 sets of gametic chr on same mitotic spindle |
| What chr do humans have? | 22 pairs of autosomes common to both sexes, 1 pair of sex chr -> XX (homogametic -> female), XY (heterogametic -> male) |
| What sex chr do chickens have? | WZ (heterogametic -> female), ZZ (homogametic -> male) |
| What is the evolution of the Y chr? | 2-300 million years ago -> autosomal acquisition of SRY -> proto-Y chr -> antagonist mutations/inversions -> suppress recombination opportunities -> repetitive sequences/deleterious mutations accumulate -> truncated -> genes selected for sex determination |
| What is the charcterisation of genetic sex? | Y chr present/absent |
| What is the characterisation of gonadal sex? | Testis present/absent |
| What is the characterisation of somatic/phenotypic sex? | Male -> penis, scrotum, prostate, vas deferens, female -> clitoris, vagina, uterus, oviduct |
| What is the characterisation of brain sex? | Male -> constant HPG activity, female -> cyclical HPG activity correlating w/ menstrual cycle |
| What does presence of SRY gene produce? | Male gonadal phenotype w/ testes |
| What is Turner's syndrome? | XO -> female gonadal sex -> ovary present |
| What is Kleinfelter's syndrome? | XXY -> male gonadal sex -> testes present |
| What is XY*? | Deletion of part of Y chr (no SRY gene) -> female gonadal sex -> ovary present |
| What is XXSxr? | X-Y translocation of SRY from Y chr to X chr -> male gonadal sex -> testes present |
| What and when is female X inactivation? | All X chr apart from 1 is inactivated as inactive Barr bodies -> prevent X gene overdosage -> random selection among cells in epiblast at primitive streak stage |
| Where is SRY expressed and what is its structure and function? | Expressed in genital ridge (not PGCs) -> encodes 223 aa DNA/RNA binding protein (79aa HMG box as master TF -> conserved DNA binding domain) -> affect SOX9/3 gene expression (accessibility/stability) -> gonad differentiation (Wolffian duct) |
| Where do PGCs originate from? | Differentiate in amnion (endoderm) via OCT4 -> migrate onto caudal yolk sac -> migrate to genital ridge on posterior dorsal mesentery |
| Where is SRY switched on in males and what are the effects? | SRY switched on in Sertoli cells -> seminiferous tubule formation -> connect w/ degenerating rete testis mesonephric tubules, SRY switched on in stromal Leydig cells -> androgen production -> maintain mesonephric duct |
| What does the Sertoli cell produce and what are the effects? | Produces anti-Mullerian hormone (AMH) -> stimulate paramesonephric duct degneration/uterine primordium regression |
| What duct do males have? | Mesonephric duct -> epididymis, vas deferens, seminal vesicle |
| What happens to individuals w/out SRY? | Sertoli cells degenerate, coelomic epithlium proliferates to form cortical cords -> surround oogonia to form primordial follicles |
| What duct do females have? | Mesonephric duct degenerates -> no Leydig cell androgens, paramesonephric duct -> maintained by lack of AMH, oviduct, uterus, cervix, top 1/3 of vagina |
| How do the male external genitalia differentiate? | DHT (dihydrotestosterone) -> converted from testosterone by 5-alpha-reductase -> development of penis, scrotum, vasa, accessory sex glands |
| What is the cause and effect of guevodoces? | Mutated 5-alpha reductase -> testosterone not converted to more potent DHT -> no differentiation of male external genitalia |
| What is primary hermaphroditism? | Gonadal anomalies -> mixed ovarian/testicular tissue in 1/both gonads (partial/mixed gonadal dysgenesis - ovotestis), sex chr mosaicism -> mitotic recombination removes SRY -> some tissues differentiate fe/male -> low androgen -> incomplete masculinsation |
| What is secondary hermaphroditism? | Somal anomalies -> androgen insensitivity (poorly developed male soma), congenital adrenohyperplasia/adrenogenital syndrome (ovary + variable somatic maleness), micropenis, hypospadias (urethra opens into ventral penis/vagina) |
| What is the cause and effect of androgen insensitivity syndrome? | Mutated androgen receptor -> feminisation of XY -> mutation in ligand binding domain, testosterone cannot bind androgen receptor -> no male external genitalia |
| What is the appearance of androgen insensitivity syndrome? | Phenotypically female (no male external genitalia), gonadally/chromosomally male (SRY gene present) |
| How does androgen insensitivity syndrome present? | 'Female' patient presents at puberty w/ no menstrual cycle/breast development -> treat w/ female hormones to support female development, remove testes (no scrotal sac so higher temperatures predispose to testicular cancer) |
| What is the cause and effect of congenital adrenal hyperplasia? | Deficient 21-hydroxylase enzyme (low cortisol production from adrenal cortex) -> no -ve feedback on hypothalamus/ant pituitary -> increased CRH/ACTH production -> adrenal androgens produced -> bind to androgen receptor -> stimulate male differentiation |
| What is the appearance of congenital adrenal hyperplasia? | Phenotypically weak male (external male genitalia), gonadally/chromosomally female (XX) |
| What internal genitalia are present in congenital adrenal hyperplasia? | No SRY (XX) -> no testes/androgen/AMH production -> female paramesonephric duct maintained -> uterus, oviducts, cervix, upper 1/3 of vagina |
| How does congenital adrenal hyperplasia present? | Micropenis w/ empty scrotum (no testes) -> treat w/ surgical removal of male genitalia -> ovaries intact so fertility not compromised |
| What is the apperance of guevedoces? | Phenotypically female (no male external genitalia), gonadally/chromosomally male -> (SRY gene present) |
| What internal genitalia are present in androgen insensitivity syndrome? | SRY present (XY) -> normal testes/androgen/AMH production -> regressed female paramesonephric duct -> epididymis, seminal vesicle, vas deferens |
| What internal genitalia are present in guevedoces? | SRY present (XY) -> normal testes/androgen/AMH production -> regressed female paramesonephric duct -> epididymis, seminal vesicle, vas deferens |
| How does guevedoces present? | Urethra opens near anus -> treat w/ increased testosterone at puberty to drive penis formation |
Created by:
vykleung
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