Week 12 Flashcards
Sexual Dimorphism
Differences in phenotype of the two reproductive species
Bipotential Gonads
Mullerian duct
Wolffian duct
Exist in both males and females during fetal development, set of cells make up either gonads.
During fetal development males and females are indistinguishable.
Male development
Secretion of Testosterone and antimullerian duct hormone trigger regression of the mullerian duct (MIH) and development of the wolffian duct into the urethra and vas deferens (testosterone)
Female development
Wolffian duct is degraded due to the lack of testosterone and the mullerian duct develops into parts of the vagina, uterus and cervix due to the lack of MIH
How does sec determination occur?
sex of the gonad cells can influence the development of the bipotential gonad, these sex hormones control secondary sex characteristics
Genetics of Sex determination
1- DNA sequence variations affecting sex determination are generally viable but may be sterile
2- DNA sequence variations have clear phenotypes
Androgen insensitivity syndrome
XY
Testes
Female secondary sex (genitals) characteristics
Androgens are secreted, the gene encoding androgen receptors on the X-chromosome is inactive. The presence of androgens can be detected.
testosterone cannot act because there were no receptors
-no wolffian duct, no mullerian duct, just testes and urethra
Heterogametic systems (humans/drosophila)
Male (heterogametic): XY
Females (homogametic): XX
Heterogametic systems (Birds/Butterfly)
Male (homogametic): ZZ
Female (heterogametic): WZ
many mechanisms determines sex
X0 and Haplodiploid systems
Male: X0
Female: XX
Male: 1n
Female: 2n
Gated Systems
Temperature and social systems in turtles (temperature) and fish (social systems)
Which Chromosome is humans is repsonsible for determining sex?
The presence of the Y chromosome
One X is sufficient for female development (Turner’s syndrome)
XX Male
Sex reversal gene on the Y chromosome (sry) translocation of sry onto the X chromosome
XY female
Deletion of sry on the y chromosome
SRY
Encodes a transcription factor. Secretion of androgens and anti-mullerian hormone present in male gonads but not in females
Sex determination in drosophila
the presence of the Y chromosome is not important for male development, the y chromosome has some gene that are important for fertility but not sex determination
Drosophila primary sex determination
Polyploid in drosophila
X;A, 0.5 = males
XX; AA 1>= Females
0.5/1 Ratio
In males the 0.5 ratio does not transcribe enough tf to bind to the sxl gene promoter no sxl is produced
In females the 1 ratio is enough to produce the tf required for sxl gene expression and sxl product
SXL males
Binds to intron of TRA pre-mrna
in males there is no SXL to bind to the intron of TRA pre-mRNA and U1 binds to the 5’ss and U2AF binds to the male 3’ss
Mature tra messenger rna with an early stop codon resulting in an inactive truncated tra protein
SXL in females
SXL binds to the intron of TRA pre-mRNA
SXL pushes U2 to use a 3’SS furhter down the pre-mRNA. SXL blocks the use of the male 3’SS
When SXL protein is present the female transcript is produced resulting in the expression of TRA protein.
TRA
transformer protein is produced when SXL tf binds
TRA activates TRA2 when it binds to it
Doublesex (dsx)
Alternative splicing of dsx is responsible for the last important step of somatic sex determination.
TRA2 is expressed in both males and females
no tra in males to activate tra2
tra2 is inactive in males leading to splicing that results in male dsx
Loss of DSX function
Partially formed male sexcombs
male claspers and vagina,
male pigmentation
genitals are both male and female
DSXM
Suppresses female differentiation
male sex combs
no vagina
male colouring
claspers
DSXF
Surpresses male differentiation no sex combs femlae colouring no male genetalia vagina
Double sex genes in turtles
Red eared turtle
26 c- male: dmrt is expressed, loosens chromatin (euchromatin;epigenetic phenomenon)
31 c-female
Behaviour
Responses of an organism to stumuli
includes neurobiology but is not exclusive to neurobiology
you don’t need to have a nervous system (chemotaxis, mating pheromones, sunflowers following the sun)
Behavioural genetics
Analysis of genes required for behaviour
Drosophila male courtship behaviour
Vibrate wings to sing tapping orienting licking attempting copulation
if the female is receptive to courtshil behaviour they will receive the male, if not the female will kick the male in the head
Genes responsible for male courtship behaviour
Tra+Tra2 in females force the splicing of the fruitless mRNA so that no aactive gene product is formed
Fru gene
Multiple promoters
fru loss-of-function alleles results in a lack of male courtship behaviour
Splicing transcripts from the P1 fru promoter (alternative _’ splicing)
5’
splicing
fru female TRA+TRA2 results in extra information in female transcript, no product is detected from the transcript even is it can be translated (tra2+tra forces the splice machinery to use 5’ splice site further 3’)
in males tra2 binds to the binding sites in the extra region to splice it out
What would happen if the TRA2 binding sites were removed?
The splicing machinery cannot be forced to use the female splice site
Females exhibits male behaviour
Connectomics
Systematic mapping of the neurons and synapses in an organism.
Sliced the nematode worm in crossections and at each section they are able to track the neuronal by stakcing them against one another, giving a neural representation of the neurons of the c.elegans brain
How can the presynaptic neuron be activated independently of a signal?
Light activated pores can be used to stimulate action potential. Opsin’s are activated by a center wavelength of light to allow ions to flow
Used in vertebrates to manipulate the activity of neurons, used a focused beam of light to stimulate cells expressing opsin.
Express proteins specifically in neurons
Binary system
driver and uas line
Visualize neurons expressing gal4, gives us info on where gal4 is expressed
