gonads and gametes - NOT USED Flashcards
D: sex
the process by which a genetically novel individual is formed as the result of mixing of genes from two or more individuals
The core elements of sex are highly conserved across virtually all eukaryotic lineages and are:
?
MEIOSIS – the generation of haploid gametes
SYNGAMY – the coming together of the two sets of gametic chromosomes on the same mitotic spind
Mammals = ____ offspring, but ___ of genetic diversity
Mammals = few offspring, but lots of genetic diversity
T or F
◦it’s not universal which sex is homogametic
T
eg, a female chick may have XY (two differnet ones)
whats meant by dosage compensation/
◦X chromosome contains the majority of the genetic material, therefore in XX females one of the X chromosomes is inactivated on a random basis = forming a barr body (done at epiblast stage of development) = equalises expression of genes between members of different biological sexes
what are barr bodies
Barr bodies (dense masses of chromatin seen adjacent to the nuclei, visualised using Carbol Fuschin staining)
how did the Y chromosome evolve?
First step thought to be the acquisition of a male-determining gene to form a proto-Y chromosome.
Further acquisition of antagonistic mutations, aided by a series of inversions, suppresses opportunities for recombination
Lack of recombination leads to accumulation of repetitive sequences or deleterious mutations, which are then deleted
T or F
where the X chromosome largely resembles the autosome from which it derived, and the Y chromosomes has lost most of its ancestral genes, and may instead have accumulated repetitive DNA.
T
D: Karyotype ..
Karyotype – complement of chromosomes within a cell
describe turners syndrome
Turners (45XO – X usually comes from the mother due to non-disjunction from the father)
describe Klinefelter’s syndrome
(47XXY – due to non-disjunction by either the mother or father)
what is nondisjunction
- (Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division)
what is a persons somatic sex?
Somatic = penis, scrotum, prostate, vasa – vs clitoris, vagina, uterus, oviducts
what is teh defauly state (sex wise)
the female
describe SRY
transcription factor encoding a DNA /RNA binding protein
on Y chromosome
encodes the HMG DNa binding box
Affects the expression of a number of other genes (eg. SOX9, SOX3) involved in gonad differentiation, but precise molecular mechanisms not yet understood
Disruption between genetic and gonadal sex = v rare (primary ___________)
Disruption between genetic and gonadal sex = v rare (primary hermaphroditism)
Primary (True) Hermaphroditism:
describe
◦Also known as intersex
◦Can be:
◦Ovary on one side and testis on other (rare)
◦mixed ovarian testicular tissue in one or both gonads (partial or mixed gonadal dysgenesis, more common and often seen where sex chromosome mosaicism exists
form both sexes - where do the gonads arise from?
the genital ridge
what week is the genital ridge formed in?
5
Genital ridges form during 5th and 6th weeks on medial side of the……
Genital ridges form during 5th and 6th weeks on medial side of the mesonephric ridges
the gential ridge is colonised by?
Colonised by primordial germ cells migrating from the extraembryonic mesoderm close to the yolk sac.
where do the primordial germ cells come from?
germ cells differentiate from the amnion as a result of wnt3A signalling from the cytotrophoblast.
This, along with chemoattractant production at the gonadal ridges, triggers the migration of the primordial germ cells (common origins of spermatozoa and oocytes) from the extraembryonic mesoderm, into the caudal part of the yolk sac, and then along the dorsal mesentery into the genital ridges.
Occurs via amoeboid movement
at the formation of the primitive sex cords - is there male or female characteristics yet?
no - SRY hasnt come into play yert
do primordial germ cells determine sex?
NO
primordial germ cells are influenced by the environment they are in – they do NOT determine sex – their arrival just triggers sex specific gene expression, driving sexual differentiation
are the gonads bipotential before SRY activation?
yes
MALES:
◦SRY expression in the _________ cells then drives male gonadal differentiation
◦SRY expression in the mesenchymal cells then drives male gonadal differentiation
for male developemnt:
describe week 7:
◦WEEK 7
◦Here, the sex cord cells proliferate, and form testis cords (Sertoli cells). Germ cells are incorporated into these
MALE Development
describe week 24
◦Testis cords anastomose and connect with remnants of the mesonephric tubules, the rete testis.
◦Leydig cells differentiate from mesonephric mesenchyme.
when at what do letdig cells differentiate from?
◦Leydig cells differentiate from mesonephric mesenchyme.
week 24
◦Sertoli cells produce …
◦Sertoli cells produce Müllerian Inhibiting Substance
◦Leydig cells produce….
◦Leydig cells produce androgens
bascially describe how a bipotential thing differentiates into a male
- SRY switched on in cells of the sex cords (sertoli cells) and in stromal cells (Leydig cells)
- sertoli cells proliferate to form smeiniferous tubules
- Seminiferous tubules connect with degenerating mesonephric tubules of the rete testis.
- Androgens from Leydig cells maintain the mesonephric duct,
- and Müllerian Inhibiting Substance from Sertoli cells stimulates degeneration of the paramesonephric duct.
describe how a bipotential thingy turns into a female
- No SRY
- Medullary sex cords degenerate
- Coelomic epithelium proliferates to form cortical cords
- Cells from cortical cords surround oogonia to form primordial follicles.
- Absence of androgens causes mesonephric duct to degenerate.
- Absence of Müllerian Inhibiting Substance permits maintenance of the paramesonephric duct.
Leydig cells produce what?
effect?
Leydig cells
androgens
Development of penis, scrotum, vasa, accessory sex glands
tistis produces what hormone? (its like something)
effect?
testis
Insulin like hormone 3
Gubernaculum contraction - testis descent
what substance do sertoli cells produce?
sertoli cells:
◦Müllerian Inhibiting Substance
Uterine primordium regresses in males
what does the gonadal sex in males depend on ?
endocrine stuff
androgens cause the growth of the ………
◦Androgens – cause growth of the mesonephric duct;
eventually forming the vas deferens, epididymis and the seminal vesicles
what does MIS do?
◦degrades the paramesonephric duct
Differentiation of the external genitalia is driven primarily by ….
Differentiation of the external genitalia is driven primarily by dihydrotestosterone (DHT
DHT is produced from ….
DHT is produced from testosterone by the activity of the enzyme 5 alpha reductase that is present in the local tissues
what does absence of 5 alpha reductase lead to?
female genitalia
Mesonephric duct = …..
Paramesonephric duct =…..
alternative names
Mesonephric duct = wolffian duct
Paramesonephric duct = Mullerian duct
mesonephric duct remnant =…..
mesonephric duct remnant = Gartner’s cyst in wall of vagina
diference in HPG axis for men and women
◦Somatic sex development involves ….
◦Somatic sex development involves the formation of both the internal and external genitalia
somatic sex development is:
◦Endocrine ________ in the male, _________ in the female
◦Endocrine dependent in the male, independent in the female
3 main hormones in somatic sex for males
◦3 main hormones
- Androgens – stimulates development of the bipotential genital tubercle to form the glans of the penis. It also triggers fusion of the urogenital and labioscrotal folds, and development of the prostate
- MIS – causes uterine primordium to regress
- Insulin-like hormone 3 (INSL3) – causes the gubernaculum to shorten and the testes to descend
INSL3 – produced by the …..
INSL3 – produced by the Leydig cells
describe how somatic sex is hormone dependant in females
◦Hormone independent:
- Uterus forms from the medial fusion of the inferior portion of the paramesonephric duct at the midline
- Upper 1/3 of the vagina from the paramesonephric duct, lower 2/3 from the urogenital sinus
- Bipotential genital tubercle bends caudally to form the clitoris
- Genital swellings and urethral folds form the labia majora and minora respectively
describe masculinisationof the brain
There is evidence of differences between male and female brains at various levels:
Structural – e.g. size of certain areas
Chemical – e.g. level of transmitters
Physiological – e.g. metabolism, cyclicity
Psychological – e.g. gender, aggression
Cognitive – e.g. verbal fluency, spatial ability
manifestations of Primary hermaphroditism or intersex
- anomalies of the gonad
ovary on one side and testis on other (rare)
mixed ovarian testicular tissue in one or both gonads (partial or mixed gonadal dysgenesis, more common and often seen where sex chromosome mosaicism exists, eg somatic loss of Y or translocation to X.
describe the physical manifestations of secondary hermaphroditism or intersex
anomalies of soma
Testicular feminisation or Androgen insensitivity syndrome (complete = testis + female soma 0.005%; partial = poorly developed male soma 0.01% of births)
- Congenital adrenohyperplasia or Adrenogenital syndrome (ovary + variable somatic maleness: partial 1%, complete 0.01% of births)
- Micropenis (poorly developed phallus 0.002%)
- Hypospadias (urethra opens in ventral penis or in vagina 0.05-0.2% of births)
describe congenital adrenal hyperplasia
CAH
- XX
- Deficient in 21-hydroxylase (enzyme that converts progestogens to corticosteroids)
- Results in an increase in precursors, which are then shunted down the androgen synthesis pathway
- In males this results in precocious puberty
- In females this causes the mesonephric duct to persist and external male genitalia to form = potentially a blind ended vagina and micropenis
describe 5-alpha reductase deficiency
5-alpha reductase deficiency
- XY
- Known as Guevodoces
- Unable to make peripheral DHT
- May present with ambiguous genitalia/micropenis at birth, undergo virilization at puberty with androgen surge
- But urethra often remains opening near the anus
- Most are heterosexual
describe androgen insensitivity
Androgen insensitivity syndrome
- XY
- Have normal testes and androgen production – often phenotype is less severe than textbooks suggest as some DHT may be able to bind:
- Completely female = 0.005%
- Poorly developed male characteristics = 0.01%
- At puberty when there is a surge of androgens – secondary sexual characteristics may develop
- Due to mutations in the androgen receptor in peripheral tissues
describe Hypospadia
Hypospadia (urethra opens into ventral penis/vagina)
Treatment for Congenital Adrenal Hyperplasia is generally ….
Treatment for Congenital Adrenal Hyperplasia is generally glucocorticoid replacement therapy, usually in the form of hydrocortisone.
is the concept of gender learned>
yess
gender:
◦2 years =
◦3 years =
◦5 years =
◦7 years =
◦2 years = identity
◦3 years = role
◦5 years = constancy
◦7 years = policing
D: puberty
◦State of transition encompassing all physiological, morphological and behavioural changes when developing from a juvenile to a fecund
what are the effectors of puberty?
◦Steroids are the effectors of puberty
D: ◦Gonadarche –
◦Gonadarche – level of maturation required to produce gonadal hormones
Puberty is considered precocious if secondary sexual characteristics occur before the age of _ in girls and _ years in boys
Puberty is considered precocious if secondary sexual characteristics occur before the age of 8 in girls and 9 years in boys
◦What are the main regulators of puberty and where are they produced?
◦GnRH - produced by neurons in the hypothalamus and released into the pituitary portal vein to the anterior pituitary
◦FSH and LH– released from the anterior pituitary in response to GnRH
◦In males
◦Testicular androgens
◦In females
◦Ovarian oestrogens
◦Androgens from the ovary and adrenal gland
