Lecture 6 Flashcards

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1
Q

What are the 5 ways of determining sex in organisms?

A

1.Environment 2.Genes 3.Haplo/diploidy 4.Balance of autosome to sex chromosomes 5.Sex chromosome

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2
Q

How is sex determined in marine worm?

A

–combianation of genetic and environmental marine worm (Bonellia viridis), female is like a tube, little larvae get out of her and sex is determined by how far they fall from the mother’s proboscis, if close = male. Releases a chemical switching on the maleness gene.

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3
Q

How is sex determined in reptiles?

A

-environmental reptiles- incubation temperature of eggs lizards and alligators- higher temperature = more males turtles = higher temperatures = more female -temperature affects the production of sex hormones in turtles cholesterol—testosterone (aromatase can change it to oestrogen) -in higher temperature more aromatase = more oestrogen= females

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4
Q

How can genes change the phenotype in drosphilas (tra)?

A

Drosphila: XX-female XY-male tra+ needed for normal female development tra= mutant allele at the transformer locus, switches what we’d expect to be a female to the male phenotype (not the other way around) tra tra XX- phenotypically male (missing the tra+ so can’t be female, happens only when tra homozyg.) tra tra XY- phenotypically male (no change)

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5
Q

What are disorderd of sexual development?

A

Disorders of Sexual Development (DSD) Human: androgen insensitivity locus on the X chromosome (testicular feminisation) tfm- testosterone receptor so XtfmY appear as females -females can be carriers and then the baby boy phenotypically a female, they have internal testes, the tissues normally sensitive to testosterone aren’t because of the defect in the testosterone receptor (have the testes removed as the internal ones increase chances of cancer)

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6
Q

How is sex determined in honey bees?

A

-haplo/diploidy honey bees (and others from the Hymenoptera family) female bees- workers and queen – diploid 2N- arising from fertilised eggs- heterozygous males- drones- haploid N- arising from unfertilised eggs- hemizygous at the locus -femaleness associated with being heterozygous -for any locus males have one allele (hemizygous), Queen has two so can be hetero or homozygous -royal jelly fed to a female triggers the gene expression for a queen, when mature goes for nuptial flight, gets sperm from a male, stores it and produces eggs, some are fertilised and some unfertilised by the sperm she has stored -non-reproductive females share the genes from the father and 50% of the Queen’s so on average they share 75% of their genes

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7
Q

What is unusual in drosphila sex determination?

A
  • unusual because it doesn’t rely only on sex chromosomes but also on the ratio of the X chromosomes vs the autosome chromosomes (X/A)
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8
Q

What are the normal ratios of X versus autosome chromosome in drosphilas?

A

if X/A= 1 female, normal females are AAXX so 2/2= 1 then sxl gene on if X/A= ½ male, normal males are AAX so ½= ½ then sxl gene off

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9
Q

What is the sxl gene (drosphila)?

A

sex lethal gene- required to complete female differentiation numerator-product of X denominator- product of A in the X/A equation to switch on the sxl gene need numerator (X) dimmers (so two Xs), then sxl switches on which is required for the normal function of the tra gene to produce the tra protein which is only expressed in females XX dimmer switches on sxl gene-sxl protein- switches on tra gene—tra protein -in a male fewer Xs /numerator so rarely get proteins that are homodimers both XX produced so sxl is not switched on

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10
Q

What are the phenotypes of the following drosphilas: XXAA X/A= XOAA X/A= XXXAA X/A= XYAA X/A= XXYAA X/A= XYYAAA X/A=

A

XXAA X/A= 1 female XOAA X/A= ½ male sterile XXXAA X/A= 3/2 meta female XYAA X/A= ½ male XXYAA X/A= 1 female XYYAAA X/A= 1/3 meta male Smaller than ½- male bigger than 1- female, but those are puny weak and sterile Something in between ½ and 1 (except those exact numbers) intersex= gynandromorphy (lost X in a cell line)

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11
Q

What causes maleness in humans?

A

-Y causes maleness -have to have at least one X to survive

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12
Q

Do aneuploidies cause miscarriages?

A

-over 50% of miscarriages -7.5% of all birth defects are related to DSD disorders of sexual development -1/4500 children born with a significant DSD from ambiguous genitalia to complete sex reversal -sex aneuploidies arise at meiosis (non-disjunctions in a male- end up with sperm XY and O, in female end up with XX and O, non disjunction at anaphase I or II or both)

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13
Q

What is Turner syndrome?

A

X -cause of many miscarriages (15%, 1/2000 survive) -webbing at the back of the neck -no breasts, no secondary sex characteristics, no functioning ovaries, usually infertile -birthmarks, swelling of limbs -very short (110cm) -it is very variable! Some almost normal (gymnast example)

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14
Q

What are XXX conditions?

A

-1/1200 individuals -normal, only have trouble with conception -sometimes produce viable gametes

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15
Q

What are XXXX conditions?

A

-IQ with a mean of 55, many abnormalities -speech and language delays -behavioural problems, oddly shaped legs

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16
Q

What is Klinfelter syndrome?

A

XXY -infertile, undeveloped testes -often mentally impaired but not necessarily -male phenotype -not as much testosterone so some female sexual characteristics -can lead a relatively normal life -1/500 male births

17
Q

What is XXXXX?

A

-more Xs = more severe affliction

18
Q

What is XXXXY?

A
  • Klinfelter variation -even more severe retardation
19
Q

What is XYY syndrome?

A

-controversial if it’s a syndrome or not -first described in 1961 (male: aggressive, tall and low IQ) - 2-3% of males in institutions are XYY because of mental retardation or antisocial behaviour -could plea not guilty for murder due to XYY syndrome- not anymore!

20
Q

What is XXYY?

A

-mental retardation) -characteristic hands

21
Q

What phenotype is XY deletion of tdf?

A
  • tdf = testis determining factor (caused by SRY) -appear female because they don’t have the gene causing the cascade of male sexual differentiation
22
Q

What phenotype is XX with tdf from Y?

A

-appear male because get tdf locus transferred from the Y (crossing over) hence mouse XX with SRY inserted and normal male XY look the same! Male!

23
Q

How is sex determined in humans (the process)?

A

-Up to 5-6 weeks of gestation: mass of undifferentiated tissue -after if Y chromosome present has the SRY gene that encode for the testis determining factor - if no Y present, mass turns into ovary -the start is the same for both sexes, if something goes wrong the default is female -the external genitalia parallel- clitoris=penis

24
Q

Describe the process of sex differentiation in humans. 7 steps

A
  1. undifferentiated gonads (5-6 weeks)
  2. medulla XX cortex XY(SRY)
  3. ovaries testes
  4. oestradiol AMH=antimullerian hormone (inhibition of Mullerian ducts) plus testosterone
  5. female genitalia test. converted into dihydrotestosterone by alpha 5 reductase
  6. mullerian ducts: external genitalia plus wolffian ducts develop into internal genital
  7. internal genitalia (uterus etc)
25
Q

What is andorgen insensitivity?

A

if get to dihydrotestosterone but tissues insensitive to it so don’t turn into penis etc, then get external female bits

26
Q

What is pseudohermaphroditism?

A

normal male prenatal development activation of a set of genes beginning with SRY stimulates sustentacular cells (structural support cells, here Sertolli cells) to produce hormones that lead to the destruction of female rudiments and stimulates interstitial cells to activate the biochemical pathway that produces testosterone and DHT (dihydrotestosterone) Those two promote the development of male structures.

27
Q

What is alpha reductase deficiency?

A
  • autosomal recessive
  • reduced levels can result in ambiguous genitalia (testosterone doesn’t get converted to DHT as much)
  • genotype XY- look like girls because they don’t produce enough 5 alpha reductase, till puberty then levels of testosterone increase and they turn into boys
28
Q

List attributes of X chromosome:

A

X chromosome:

  • 3x bigger than Y
  • 165 Mb of DNA
  • sequenced 801 loci so far
  • have to have at least one X to survive
29
Q

List attributes of the Y chromosome:

A
  • quite small, short arm (=p arm, petite arm) centromere quite near one end
  • long arm= mostly inactive DNA (heterochromatin)
  • 60Mb (60x10 to 6) base pairs of DNA
  • in the long arm the genes are very important for fertility
  • sequenced 53 loci so far
30
Q

What is pseudoautosomal region (PAR) ?

A

-X and Y have homologous regions on the ends

(upper arm bit) = always crossing over

31
Q

How can SRY get to the X?

A
  • if crossing over not exact SRY can be transferred to X (XX males XY females)
32
Q

Why are X and Y chromosomes called heteromorphic chromosomes?

A

-different in size and centromere position

33
Q

Heterogametic:

A

producing more than one type of gamete

Man, drosphila- heterogametic X, Y gametes

34
Q

Homogametic:

A

producing one type of gamete

Females human: homogametic- always X

35
Q

Is it in all species like in humans, females homogametic and males heterogametic?

A

No. In some species the reverse- birds, fish, butterflies Z=X W=Y (when reverse using Z and W)

Females heterogametic
Males homogametic

36
Q

Are there equal numbers of males and females?

A

no

Sperm- expected equal amounts of X and Y ones but not true
China: 113 males/100 females
At conception: 120-160 males / 100 females