Sex Determination Flashcards
(42 cards)
1
Q
what is the difference between male and female system organization
A
male: hypothalamus - gonads - paired testes - gametes (gametogenesis) - spermatozoa - sex hormones testosterone (external genitalia)
female: hypothalamus - gonads - ovaries - gametes (gametogenesis) - ova - sex hormones = estrogen and progesterone (internal genitalia)
2
Q
female reproduction functions
A
- production of ova ( oogenesis) and ovulation
- reception of sperm (for fertilization)
- transport of sperm and ovum to a common site for fertilization (in ampullary region)
- nourishment of the developing fetus internally (gestation and pregnancy) in placenta and marsupial animals
- giving birth (parturition and laying eggs)
- nourishing offspring by milk production (lactation in maamals) deriving from mammary glands
3
Q
female reproductive organs
A
- ovaries lie within the pelvic and abdominal cavities
- reproductive tract = oviduct (capture ova on ovulation, site of internal fertilization and deposition of nonembryonic egg materials (albumin) in oviparous and ovoviviparous animals),
- uterus = protective and nutritive structure for maintaining the fetus (shell gland for calcification of the egg in birds and reptiles)
- cervix = caudal portion of uterus that projects into the vagina, passageway for sperm deposition and for delivery of fetus)
- vagina = copulation and reception of sperm
- external genitalia (vulva) - labia majora and labia minora and clitoris
4
Q
male reproductve functions
A
- production of sperm continuously and in large numbers = spermatogenesis
- delivery of sperm to the female in a liquid vehicle
- generation of male sex hormones = androgens
5
Q
male reproductive organs
A
- testes are suspended outside the abdominal cavity in the skin sack called the scrotum
- reproductive tract (in sequence to sperm movement): vasa efferentia epididymis, ductus deferens, ejaculatory duct and urethra
- secretions from the male accessory sex glands provide seminal fluid ( seminal vesicles, prostate gland, bulbourethral gland)
- penis and hemipenis - deposits semen into the female
6
Q
What animal lacks male accessory glands?
A
birds
7
Q
sexual dimorphism
A
two distinct, non overlapping forms of a trait that differentiate members of the same species of sex
- ornamentation
- coloration
- size
- behaviour
8
Q
what sexual dimorphism is seen in humans
A
- gonads
- internal and external genitalia
- mammary glands
9
Q
sex differences
A
significant differences in the average of a phenotype between males and females - including sexual dimorphism
- humans: height, hormone level, immune cell composition and disease
- sex differences in complex traits can change over time
10
Q
what is the sex of an animal
A
(male or female) is defined as its the ability to produce a particular type if gamete (sperm or oocyte), along with any associated phenotypic trait (external genitalia)
- tremendously variable among species
- can be the result of expression of sex- determining genes, hormone encoding genes and environment inside and outside the body
11
Q
what 3 things can influence the sex of an animal
A
- sex-determining genes
- hormone encoding genes
- environment inside and outside the body
12
Q
intersex individual
A
- females and males can be blurred with intersex
- animal born with varying presentations of male and female genitalia
- honeycreeper ( bird can be half male half female depending on colour - blue = male green =female )
13
Q
what is sex determination
A
- process where an organism beings the development of ovaries or testes from the embryonic gonad
gonad differentiation can drive the development of other sex-specific traits through hormone production - complex integration of several molecule events that push a community of cells towards a tissue fate
- outcomes of sex determination are central aspect of phenotypic sec of the organisms
14
Q
sex determination
A
- genetic (genotypic) sex determination (GSD) all mammals, birds and some other vertebrates - also some invertebrates
- sex initiation is determined by the sex chromosomes inherited at time of fertilization
15
Q
sex chromosomes of mammals and frogs
A
- males are heterogametic XY
- females are homogametic XX
16
Q
sex chromosomes in birds and urodele amphibians
A
- males are homogametic ZZ
- females are heterogametic ZW
17
Q
sex chromosomes in insects
A
- males have one sex chromosome XO
- females have two sex chromosomes XX
18
Q
environmental sex determination (ESD)
A
- reptiles like crocodiles, lizards many turtles some fish and a few snakes
- sex determination depends on external factors (temperature)
- sex chromosomes are absent
19
Q
what is the oldest known animal sex chromosomes
A
- octopus
- males two copies ZZ
- females one copies ZO
20
Q
events in the development of reproduction system
A
- initial step in sex determination in mammals begins at fertilization by sperm ( +/- Y)
- genetic initiation of sex differentiation processes can occur in the individual animal
21
Q
promordial germ cells
A
- during formation of early embryo, a population of cells are put aside for formation of the germ line
- displaced to the definitive yolk sac and part of the allantois
- separated from the embryo so they are not influenced by other cells
22
Q
PGC migration
A
- proliferate and migrate as a group from the base of the allantois and yolk sac into the hindgut then towards the gonadal ridge
- somatic cells around the PGCs secrete chemoattractants and PGCs have receptors for these to induce their migration
- somatic cells also produce survival factors during migration to gonadal ridge
- membrane adhesion proteins help to keep PGCs grouped together during migration
- membrane receptors promote interaction with the extracellular environment for migration to proceed
- PGCs that remain outside the gonadal genital ridge largely die
23
Q
gonadal ridge
A
- also known as bipotential (indifferent) gonad because at this time of development it can differentiate along different paths (ovary or testes )
- the gonadal ridge forms near the embryonic kidneys (mesonephros )
24
Q
origin of gonadal ridge
A
- when PGCs arrive in gonadal ridge, they stimulate cells around them to grow
- compact strands of tissue = ptimitive sex cords incorporate PGCS
- forming the basic structure of the gonad
25
gonadal development
- the eventual adult structures of each ovary of testes is remarkable similar across vertebrates
- no singular factor is responsible for activation of ovary or testies development in all vertebrates
- in vertebrates, sex determination pathways tend to utilize the same cohort of genetic regulators to maintain and stabalize gonad fate
26
gonadal sex differentiation
- whether testes or ovaries develop
- determined by the presence or absence of a Y chromosome in mammals
- sex determining region of the Y chromosome (SRY) stimulates production of testes-determining factor (TDF) by primordial germ and gonadal cells
- TDF directs differentiation of the gonads into testes
- females lacking the SRY gene develop ovaries - ovarian development lacks a single genetic switch - key genes exist through that are essential for correct development
- cells without SRY express female promoting genes and inhibit male promoting genes
27
phenotypic sex
- the apparent anatomic sex of an individual
- depends on the presence or absence of testes
- testosterone, secreted by the developing testes, is reduced to duhydrotestosterone
- stimulates development od male reproductive tract and external genetalia
28
wolffian ducts
- (mesonephric ducts ) develop into male reproductive tract
- mullerian ducts regress due to anti mullerian hormone secreted by developing testes = to block female reproductive system development
- the absence of testosterone, mullerian ducts (paramesonephric ducts) develop into the female reproductive tract and wolffian ducts regress
29
the interplay of testes and ovary pathways
- strong evidence now exists that male and female sex determination pathways actively suppress one another (durin gonad differentiation, after testes if ovaries are developed )
- studies have shown that testes and ovaries are easily converted (constant expression of specific genes is needed to suppress opposing pathway and prevent transdifferentiation)
30
environmental sex determination
- environmental sex determination (reptiles, lizards turtles fish ad snakes)
- external factors
- sex chromosomes are absent
- control of differentiation of sex traits through effects of steroid hormones and other factors made by gonad
- arisen independently in multiple lineages
- involves epigenetic regulation of gene networks (altering gene expression and phenotype without altering DNA sequence Eg: methylation(repression) or demethylation (activation)
31
STAT3
in the red eared turtle, research showed transcription factor was involved in capturing temperature cues
- signal transducer and activator of transcription
- major signaling factor in response to multiple cues
32
development window
- process of ESD is cumulative
- development window durin which enviroment influences sex is long (weeks)
- changing fertlized eggs between female-promoting and male - promoting temeratures can switch the sexual program up until specific development of the gonads takes place
- the later the shift the less the animals change
33
control of sex determination
- appropriate determination, differentiation and development of gonads needs a tightly regulated network of transcription factors and cell signaling molecules
- otherwise differences (disorders) of sex development occur or DSDs
- ambiguous or maldeveloped genitalia
- gonadal dysfunction
- infertility
- complete sex reversal in both male and females
34
sex reversal
- pig and goat present a relatively high frequency compared to other species (0.1-0.6%)
35
polled intersex syndrome
- goats
- due to deletion within chromosome (Ch1) that directly transcrips of two genes, one that is associated with hornlessness (polled) and the other for ovarian development (Foxl2)
- deletion of chromosome 1 effects two genes running in opposite directions in the same region
- Foxl2 is very important for female development
36
turners syndrome
- gonadal dysgenesis
- occurs when only one X chromosome is present (XO) no YO has ever been reported suggestive tgar one X chromosome must always be present for viability
- the primordial germ cells reach the gonad but many degenerate shorty after arrival (hypoplastic ovary, small uterus, underdeveloped external genitalia)
- infertial genitalia results from lack of gonadal hormones
- most prevelant in horses - also found in humans, pigs dogs and cats
37
klinefelters syndrome
- results from non-disjunction during meiosis giving XXY
- the presence of the Y chromosome result in male determining genes influencing development
- male gonads form, produce male related hormones and thus the individual develops phenotypically as male
- presence of female chromosome drives production of female related genes such that a hypoplastic testes can result and prevention od spermatogenesis
- found in humans, dogs, cats sheep wine and cattle
38
pathenogenesis
- also considered a form pf unisexual reproduction
- among vertebrates, reproduction in complete absence of males occur in reptiles = true pathenogenesis
- since essentially a form of cloning, once thought to make species phrone to disease, mutations, paracites
39
obligate
- reproduction exclusively through asexual means
- among vertebrates found in all female species of certain lizards and snakes
40
fucultative
- reproduction in sexually reproducing species that sometimes utilizes asexual means
extremely rare in nature : stress, captivity, hormones
- no instances of facultative parthogenesis in mammals to date
41
obligate parthenogenesis steps
- requires doubling of chromosomes in egg-producing cells prior to meiosis
- enables production of eggs with complete somatice chromosome complement of mother without abandoning meiosis
42
facultative pathogenesis steps
- differs from obligate
- diploid chromosome complement of eggs restore by failure of second meiotic division of fusion of second polar body with egg nucleus
