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MSc - embryo exam > battle of the sexes > Flashcards

battle of the sexes Flashcards

1
Q

what is sex determination?

A

the development of characteristics which allow an individual to be identified as male or female

  • reproductive system - testis vs ovaries
  • external phenotype
  • behaviour - hormone induced
  • metabolism
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2
Q

what did Aristotle say about sex determination?

A

’ the heat of the male partner during interocurse determines the sex of the baby’
- if the males heat overwhelms the woman coldness then a male with form

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3
Q

in mammals what determine the sex?

A

the y chromosome

since all females are XX, all oocytes carry an X chromosome.
males are XY so sperm can carry an X or a Y sex chromosome.
so the male partner determines the sex of the offspring

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4
Q

what gene determines the sex?

A

SRY gene - sex determining region Y - one found on the Y chromosome
SRY gene encodes transcription factors that activate testis formation (testis determining factor)

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5
Q

how does SRY gene determine sex?

A

several testis specific genes contain SRY-binding sites in their promoters
binding of SRY to these sites initiates testis development

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6
Q

what is meant by biopotential embryonic gonad?

A

the gonads are gene driven
early embryonic gonad is indifferent or biopotential
formation of embryos or testis is an active gene directed process (no default process)

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7
Q

when does sex differentiation occur?

A

at 7 weeks of development

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8
Q

what are the two stem of ducts?

A

wolffian - male
mullerian - female

development of ducts is hormone dependant.

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9
Q

which phenotype predominates if the gonads are removed?

A

if the biopotential gonads are removed the female reproductive system develops

female phenotype predominates

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10
Q

how do males develop?

A

in humans SRY gene stimulates the indifferent gonad to form a testis
the testis produce two hormones
- testosterone (forms male reproductive organs, wolffian duct - vas deferens, inhibits breast primordia)
- anti-mullerian hormone (degeneration of mullerian duct

testis determining factor (encoded by SRY gene) activates SOX9 - testicular development and sertoli cell proliferation
SOX9 induces steroidogenic factor 1 SF1 - up regulates AMH from sertoli cells and increases production of testosterone in leydig cells

XX humans with an extra copy of SOX9 gene develop as males despite SRY absence.

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11
Q

what gene appears to stop SRY

A

DAX1

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12
Q

what two genes stimulate biopotential gonad to form an ovary?

A

DAX1 and WNT4

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13
Q

how does the female develop?

A

DAX21 and WNT4 stimulate the biopotential gonad to develop into an ovary
ovary secretes oestrogen
oestrogen acts on mullerian duct
development of uterus , oviducts and cervix.

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14
Q

is it only the male chromosome that influences sex of offspring?

A

since equal number of X?Y sperm are produced, there should be equal numbers of female/male offspring

but environment had a strong influence in some species.

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15
Q

how is the snapping turtle egg affected when incubated at different temperatures?

A

bellow 22 or above 29oC = females

intermediate temps = males

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16
Q

how is the american alligator egg affected when incubated at different temperatures?

A

above 30oC = females
below 25oC = males
at 28.5oC = equal numbers

17
Q

in reptiles what determines sex?

A

genotypic sex determination
also a thermo-sensitive period of development
Australian skink
-males XY
- females XX
- low temp: genotypic xx females become phenotypic males XXmales

Australian dragon lizard

  • males ZZ
  • females ZW
  • high temps: genotypic ZZ males become phenotypic females ZZ females
18
Q

why does temperature affect sex differentiation?

A

high temperatures increase aromatase

  • converts androgens to oestrogen
  • biased sex ratio towards females
19
Q

what are the advantages of skewed sex ratio?

A

sex allocation hypothesis

  • dominant males father most offspring
  • subordinate males do not mate
  • all females will get pregnant
  • but only females with high rank/body condition will produce males which join the dominant reproducing males.

so to maximise reproductive output

  • females with good condition should opt to produce male offspring
  • females with poor condition should opt to produce female offspring

supported in many wild species including deer an mice

20
Q

why may adaptive control of genes bias occur? which species may it occur in?

A

in many non-mammalian species

evolved as a response to changing environmental conditions e.g. food availability, temp, disease, population density, maternal condition, season

21
Q

what is an adaptive control of gender bias in fig wasp?

A

low population density - sex bias in favour of males

- disperse to fertilise females in other colonies, maximise genetic potential and minimise inbreeding

22
Q

what is an adaptive control of gender bias in ruffs?

A

poor food availability - sex bias in favour of females

  • maximise offspring numbers, cost to mothers,
  • don’t waste food on multiple males - you only need one male
23
Q

what affects offspring sex ratio in red deer?

A

maternal dominance correlates offspring sex ratio
- dominant females have more male offspring (dominance correlates with testosterone concentration
this sex bias is eliminated with high population density - nutritional stress and increased confrontation to maintain dominant position

24
Q

what affects offspring sex ration in american opossum?

A

maternal condition correlates offspring sex ration
- increase in male offspring with high n-3 fatty acid diet
- marsupials move to the pouch 14 days after conception
mechanisms must act before conception or very early om

25
Q

what affects offspring sex ration in non human primates?

A

– Maternal condition correlates offspring sex ratio
– Social structure is important
• Colobine monkey high ranking females have more
males
• Opposite is true in baboons (matriarchal society)

26
Q

do humans show adaptive control of gender bias?

A
  • socioeconomic variables (famine)
  • environmental stressors
  • psychological stressors
27
Q

how does preconception nutrients affect sex ratio?

A

Pre-conception nutrition
Maternal diet high in unsaturated fats or glucose
• Increasedmalesborn Maternal diet high in omega-6
polyunsaturated fatty acids (vegetable oils) • Increasedfemalesborn
Recent evidence: not a consistent dietary intake that determines offspring sex, but a change in nutritional status
• Females gaining condition produce sons
• Females losing condition produce daughters

28
Q

environmental stressors effect offspring in humans?

A

Exposure of males to endocrine disruptors skews sex ratio in offspring
Dioxin exposure of males at puberty
• Bi-product of chemical, steel/iron industry
• Increased male offspring in adulthood
Dichloroethylsulphide (Mustard gas)
• Exposure of Iranian soldiers during the Iran-Iraq war
• Decreased male:female ratio in offspring
• Decreased testosterone:gonadotrophin ratio in males
• Increased sperm DNA damage
– Sperm DNA integrity linked to ability
to progress through the female tract
– Are Y chromosome sperm more susceptible to chemically induced DNA damage?

29
Q

psychological stress in humans affect sex ratio?

A

Severe life event pre-conception or early pregnancy
– Death/cancer diagnosis in spouse or child
– Decrease in male:female sex ratio
–>Differential fertilisation – more X chromosome sperm fertilised? or Differential embryo survival–more XY embryos aborted?

Kobe earthquake and 10-day war in Slovenia – Both resulted in decrease in male:female sex ratio
– Reduced sperm motility
• Stress induced increase in prolactin and testosterone in males
• Interfereinspermatogenesis
• Differential effect on X or Y bearing spermatozoa?

Confounding factors with psychological stress!
– Sexual abstinence
– Hormone concentrations differ from the norm
– Poor nutrition
– All affect semen quality and embryo survival

30
Q

how might fathers influence the sex of their children? (preconception)

A

Natural inseminations from the most fertile males result in increased male offspring
– Sons likely to disperse
– Fathers pass on genes without competitive threat

Paternal influence on sex ratio related to sperm variation
– Biochemical
– Morphological
– Ability to fertilise

But, is there evidence that X and Y sperm differ?

31
Q

how might mothers influence the sex of their children?

A

As the female has a disproportionate role in production of offspring it is likely that most influence on offspring sex ratio is under maternal control

Female reproductive tract might control gender bias – Sex specific sperm selection/progression?
– Sex specific fertilisation?
– Sex specific embryo implantation/survival?

Less ‘costly’ for female to manipulate gender bias before/at fertilisation than later during pregnancy

32
Q

how is the female reproductive tract selective?

A

Female tract is not passive – it controls sperm progression
– Pig, 30 billion sperm inseminated, but only 1000-5000 reach oviduct
– Human, conception falls 40% to 24% <1.5 million sperm inseminated

Cervix: mucus removes DNA damaged sperm
– Possibly because DNA-damage is reflected in poor motility

Uterus: immunological (neutrophils) removes membrane damaged sperm

Utero tubal junction
– Prevents 90% of sperm in uterus
passing into oviduct
– Restricts entry to minimise polyspermy
– Opportunity to exercise choice

Oviductal storage/selection

Controls which sperm are given access to the oocyte

33
Q

is there sperm selection at utero tubal junction?

A
  • molecular recognition system in place
  • failure to express sperm surface proteins
    A-disintegrin and metalloprotease 3 (ADAM3)
    other surface proteins identified for UTJ

there is evidence for sperm selection via surface proteins

do these sperm serfuca proteins reflect genetic quality
is the sex-specific sperm selection via molecular recognition

34
Q

what evidence is there that sperm surface markers reflect genetic information?

A

electronegative charge of sperm plasma membrane correlates with DNA integrity in sperm nucleus.

  • negative charge correlates with stage of epididymal maturation
  • chromatin fragmentation and nuclear integrity related to epididymal maturation.
  • negative charge on sperm attributed to CD52 (membrane anchored glycoprotein with highly charged N-linked carbohydrate moiety, CD52 added to sperm during epididymal maturation)
  • CD52 involved in sperm binding to oviductal epithelial cells and zona pellucida - female tract can select sperm genetic profiles via membrane bound CD52
35
Q

how can the female reproductive tract select good sperm?

A
  • negative charge on sperm attributed to CD52 (membrane anchored glycoprotein with highly charged N-linked carbohydrate moiety, CD52 added to sperm during epididymal maturation)
  • CD52 involved in sperm binding to oviductal epithelial cells and zona pellucida - female tract can select sperm genetic profiles via membrane bound CD52

Sperm surface markers of genetic information
• Female tract can bind/select sperm using CD52 as a marker of genetic integrity
• So, we know female tract uses sperm surface molecules to identify DNA damage to maximise fertilisation
• What other molecules exist?
• Do molecular expression patterns differ between X and Y sperm?
• Might expression patterns be manipulated by environmental stressors known to skew gender bias?

36
Q

are X and Y chromosome sperm different?

A

Nuclear content differs by 2.8-4% dependant on species
• Morphology differs subtly between X and Y sperm – X sperm increased head, mid-piece and tail length
– Sperm morphology reflects DNA integrity
• Differentially expressed proteins
– Associated with cytoskeletal structures
influencing motility
– Regulation of metabolism
• Glycolyticenzymesandcalmodulin
– Levels of expression NOT presence/absence of gene product
• Individual sperm microRNAs
– Adopt unique 3D shapes for sperm recognition in oviduct – Powerful modulators of gene expression

37
Q

where may mothers manipulate offspring sex by sperm selection?

A

progressions at UTJ and oviduct

fertilisation (zona pellucida)

MSc - embryo exam (13 decks)

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