CBG16 Flashcards
In honet bees what is the gene to determine sex?
complementary sex determining gene csd
How does csd gene work?
targets feminizer gene needed for female development
which then makes product that acts on double sex gene.
haploids are hemizygous and become males as dont produce feminizer gene
alternative splicing in males adds stop codons into feminizer coding sequence
females=2n males=n
When might a male honey bee be produced by fertilisation?
the locus for csd is honey bees is highly variable. - 13 alleles
generally females are heterozygous at the locus.
in an inbred population the locus can be homozygous
which can result in male production from fertilisation as stop codon stops feminzer.
- ussually the males die, as lethal
What is the default sex in drosophilia?
male
how are females produced in drosophilia?
sex lethal sx1 gene starts cascade of mRNA alternate splicing to produce female specific proteins.
female double sex represses male genes and activates female.
* male double sex represses female genes*
What are the chromosomes for male and female in grasshoppers?
female = XX male = X0
What are the chromosomes for male and female in humans?
female = XX, XXX, X0 male = XY, XXY
What are the chromosomes for male and female in drosophillia?
Male = XY X0 female = XX, XXY metafemale = XXX
What are the chromosomes for male and female in birds?
male = ZZ female = ZW
What is a metafemale?
low viability fruit fly with female phenotype
no. of sex chromosomes exceeds number of autosomes.
How is sex identified?
- anatomy
- endocrinology, conc of sex hormones
- chromosomes
- genes, eg. genes in testes development pathway.
What is the SRY+ gene?
male determining gene
y genes not found on X active only in testes
if present inhibits od - ovary development gene
shows homology to SOX3 in playpus
What determines sex in humans?
sry gene in males
od -ovary development gene in females
if sry present it inhibit od -> gonads, testes - boy 8weeks
if by week 13 there is no sry gene, od is switched on = ovaries- girl.
what is dsd?
disorder of sexual development
- difference between internal/external chromosomal gender identity
What sex do these chromosomes represent: XYSRY+ XXSRY+ XYSRY- XXSRY-
XYSRY+ normal male
XXSRY+ translocation from y-x
XYSRY- deletion/mutation of sry gene
XXSRY- normal female
What leads to intersex or DSD?
uncoupling of human chromosomal and phenotypic sex.
What is androgen insensitivity syndrome?
recessive mutation that causes 46XY SRY+ chromosomal males to be insensitive to androgens
leading to phenotypic female AIS
complete AIS genitalia female - no female internal organs
partial AIS = can be male female or in the middle
When can 46XY SRY+ be phenotypically female?
AIS
if DAX1 gene is duplicated on X chromosome
= anti testis gene
What is required to maintain testic function in adult males?
DMRT1 female specific genes are blocked fox12 b-catenin -rspof
What does X0SRY- genotype produce?
female
but 2X chromosomes are required for functioning ovaries.
What is required to prevent trans differentiation to testes in females?
on going presence of foxl2 in ovaries r
Give 2 examples of ESD?
environmental sex determination
eg. parthenogenetic females produce clonal females (Daphnia) but males in stress
larval setting behaviour in green spoon worm
- free swimming in sea = female
large probiscus
land on prodbiscus and become male - sperm donor. - tiny
How are turtles under the influence of ESD?
egg incubation critical at certain times in embryonic development
eg. CXPIA gene priduces aromatase converts testosterone to estradiol in gonads.
low temperates correlate with female development
What is protoandry give an example?
protoandry
begin life as male and change into female
eg. clown fish.
In what species does protogyny occur?
wrasse
female - male
