C. elegans Sex determination Flashcards
What is sexual reproduction and what are its advantages?
sexual = meiosis (to reduce ploidity before restoring diplodity upon fertilization)
gaining new genotypes to fight against unfavorable conditions and predators
faster than random gaining of mutations
What are microgametes?
What are macrogametes?
sperm
oocyte
What sex is XX in humans?
C. elegans?
Drosophila?
female
hermaphrodite
none
What sex is XY in humans?
C. elegans?
Drosophila?
male
none
none
What sex is XXY in humans?
C. elegans?
Drosophila?
Klinefelter syndrome
none
female (because of the chromosomal ratio; Y not actually a sex chromosome)
What sex is X0 in humans?
C. elegans?
Drosophila?
Turner syndrome
male
sterile male
What sex is XXX in humans?
C. elegans?
Drosophila?
none
none
dumpy hermaphrodite
Who introduced the term dosage compensation and what does it mean?
H. J. Muller
to explain that the amount of activity produced by a single gene copy of a gene on the X chromosome of a male Drosophila is equivalent to the total activity produced by the same gene when present in 2 copies on the X chromosomes in the female fly
Explain Muller’s experiment with redness of Drosophila eyes.
female flies = 2xX
male flies = 1xX
2 copy of white gene in female flies = 1 copy of white gene in male flies
1 copy of white gene in female flies while disabling the other (reducing the dosage) = white phenotype
in male flies, w gene is upregulated
(so it’s not the case of downregulating it in females)
Describe sex chromosome evolution.
2 systems:
XY = heterogametic males
AA -> AA* -> XY*
WZ = heterogametic females
AA -> AA -> WZ
autosomes retain the same diploid organisation
as the sex chromosome degenerates over evolutionary time, dosage compensation mechanisms play a role
this progressive degradation can lead to a complete loss of a chromosome
then: conversion of another autosome to sex chromosome/environmental sex determination/X:A ratio
Describe bottom up evolution of sex determination regulation.
M = TF that drives expression of male specific genes B = TF necessary for expression of M
M/m = male m/m = female but: M/M or M/m b/b is female M/M or M/m B/b or B/B is male
if the m allele is lost, B becomes in charge of sex determination
because if M always present, B is the gene that determines the sex
Write down the sex determination pathway in C. elegans.
high X:A inhibits xol-1
xol-1 cannot inhibit sdc, so sdc inhibits her-1
her-1 inhibits tra-2 (which can be activated by tra-3)
tra-2 cannot inhibit fem
fem cannot inhibit tra-1
tra-1 inhibits male fate
= high X:A worm is hermaphrodite
if xol-1 is active, it is male
(XO lethal = lethal in males = required in males = on in males)
also: mab3 is downstream of tra-1 (?), negative regulator
Which genes are required for female development?
tra - transformer
What are him mutations ad what causes them?
In which complementation groups can these mutations be sorted?
high incidence males
cause improper segregation of X chromosome
tra-1, tra-2, tra-3
Why do XXX worms have a dumpy hermaphrodite phenotype?
dosage compensation is not perfect –> too much expression of some X loci causes dpy phenotype (dpy-21/26/27/28)
