Genetics of sex Flashcards
what is sex defined as?
combing of two individual genome to make a new individuals genome
what makes human unique?
polymorphism in human genes means no two humans are genetically identical
what is recombination
a part of sex that means genes meet up in new combinations
how do bacteria recombine genes?
swap them through mechanisms such as a pillus
take up DNA from the environment and incorporate this into their genome
what does meiosis make?
haploid cells which join together in sex
how can recombination occur?
segregation or crossing over between linked genes
what is anisogamy?
differences between the gametes
what passes on an autosomal mutation?
individulas to half of offspring
what passes on an X chromosome mutations
mothers of half of offspring
fathers to daughters but not sons
males hemizygous, unmasking recessive mutations
how is Y chromosome mutations passed on?
fathers to sons
how is a mitochrondria mutations passed on
mothers to all offspring
example of autosomal disorder
cystic firbosis
example of X linked disease
colour blindness
what is the main consequence of being a sexual species?
reproduction becomes as important as surival in terms of evolution
what is the down side to sex/
it can spread diseases such as pathogens and parasites easily
what is another smaller issue of having sex?
a species genome has to be able to make both sexes
this is an issue for gene regulation
what size is the human male gene?
40mb
is there any recombination in the male gene?
no
only the pseudoautosomal regions marked PAR at the ends do and these parts alow it to connect with the X
whatis SRY?
sexdetermining region of the Y chromosome
what is PAR
pseudoautosomal region
what is MSY?
male-specific region of the y chromosome
how was it known that the Y turns something on in embryos?
studys of the karyotype of people with sex chromosome aneuploidy
hwo did karotypes of sex chromosome aneuploidies demonstrate Y turns something on to make males?
XO females have turners syndrome
so having only one X doesnt make you male
XXY are males with a syndrome so it isnt two X’s making you female
so the Y must turn something on to male the embryo male
how was SRY located
finding rare people with sex reversal syndromes
what is a sex reversal sydrome?
wrong sex phenotype for their karyotype
some has translocation: part of Y attached to other chromosomes, became males.
how did sex reversal translocations help find SRY
by finding out which parts of the Y had translocated they were able to narrow down the region of SRY and find the gene responsible
what actually is SRY?
sex determining gene
short protein of 204 amino acids
transciption factors for turning off or on genes
when is the bipotential stage?
in a mammalian gonad this is around 4-7 week
it can take the male or female route
what way of at the bipotential stage does SRY go?
male
how does SRY make males
switches on SOX9
this is also a transciponal factor and autoregulatory
positive feedback loop created
embryo stays male
what does autoregulatory mean for SOX 9
it can switch other genes on or off but aso turn itself futher on
it increases the transciption of SOX9 even more creating a positive feedback loop
what does SOX make the cell do?
switches on growth factors that make the undiffertiated cell in the gonad secrete hormones turning it into a teste making testosterone
without SOX9 what happens to the gonad cells?
undifferentiated gonad cells turn on genes such as ESR1 and FOXL2 that keep sox9 turned off
controlling sex with chromsomes causes another issue…
gene dosage
what is down syndrome
a form of aneuploidy
they have an extra chromosome
how do mammals deal with gene dosage
shut on X down entireley at random in each cell
this way males and females only have one X active and everything is equal
this happens in embroygenesis
how is X inactivation show in female mammals>
heterochromatic lump called a Barr body
what is Xic
the X inactivation centre
what does Xic contain?
4 genes:
Xist
Tsix
what is a holiday junction?
chromosomes connecting with each other via an intermediate
what can be a purpose of a holiday junction?
recombination
if the junctions are resolved in oppsosite orientations recombination occurs
what is heteroduplex dna?
areas of homologous DNA that are mostly similar can form DNA duplexes with mismatches in them
what turns a heteroduplex into a homoduplex?
cells have systems to detect and mend mismatched DNA and sort these issues out
what proofreads and mends DNA?
DNA polymerases can do this job and then mismatch enzymes can help
when can DNA damage occur?
DNA replication most commonly
then after replication
what kind of dna damage can occur after replication?
abnormal base single strand breaks base adducts thymidine dimers chemical mutagens interstrand crosslinks double strand breakd base insertions base deletions AG/ TC missmatches
what causes damage after replication?
spontaneous or UV light
what do chemical mutagens do
attack dna or interfere with replication
what encodes reverse transciptase
retrviruses and retrotransposons
what is a processed pseudogene?
mRNA after introns are removed is sometime transcribed and accidentally incorporated into the chromosome
what makes ectopic recombination more likely?
areas of high similarity in the genome
what is ectopic recombination?
regions of homology on chromsomes that are similar enough for recombination to occur causing abnormalities or deletions.
how can mutations affect mutation rates?
mutations can abolish proofreading ability of DNA polymerasse resulting in higher mutation rates
how can bacteria get around mutation rates?
some will be deficient and error prone and will die rather than mutating so their mutation rates are very low
what affects mutation rates?
selection for accuracy
trade-off against replication speed
genetic drift
