Lecture 6 Flashcards
What are the 5 ways of determining sex in organisms?
1.Environment 2.Genes 3.Haplo/diploidy 4.Balance of autosome to sex chromosomes 5.Sex chromosome
How is sex determined in marine worm?
–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.
How is sex determined in reptiles?
-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
How can genes change the phenotype in drosphilas (tra)?
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)
What are disorderd of sexual development?
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)
How is sex determined in honey bees?
-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
What is unusual in drosphila sex determination?
- 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)
What are the normal ratios of X versus autosome chromosome in drosphilas?
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
What is the sxl gene (drosphila)?
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
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=
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)
What causes maleness in humans?
-Y causes maleness -have to have at least one X to survive
Do aneuploidies cause miscarriages?
-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)
What is Turner syndrome?
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)
What are XXX conditions?
-1/1200 individuals -normal, only have trouble with conception -sometimes produce viable gametes
What are XXXX conditions?
-IQ with a mean of 55, many abnormalities -speech and language delays -behavioural problems, oddly shaped legs
Describe the process of sex differentiation in humans. 7 steps
- undifferentiated gonads (5-6 weeks)
- medulla XX cortex XY(SRY)
- ovaries testes
- oestradiol AMH=antimullerian hormone (inhibition of Mullerian ducts) plus testosterone
- female genitalia test. converted into dihydrotestosterone by alpha 5 reductase
- mullerian ducts: external genitalia plus wolffian ducts develop into internal genital
- internal genitalia (uterus etc)
