Hi,
During the learning journey to Body Worlds Exhibition at the Singapore Science Centre on 9th Feb, many of you were asking about the plastinated models of the pregnant woman and her foetus. Many were asking about the size of the human placenta and other related questions.
I think the three videos below will answer some of your questions. Also many of us really want to know exactly how birth occurs. The natural way via the vagina and the surgical way by caesarean-section. Learn more about these two birth processes now.
cesarean-section birth
normal virginal birth
virginal birth 2
Tuesday, February 9, 2010
Sunday, February 7, 2010
Sex determination systems
What do tiny insects like aphids and some sharks have in common? Read on to find out.
Do you know that not all organisms are like humans having the XY sex determination system?
Human males are XY and females are XX. (humans beings)
The female has two large sex chromosomes and the male has one large and one small sex chromosome.
The other systems are:
(1) XX female and XO males (grasshopper, cockroaches and crickets)
The females have two sex chromosome and the male has only one sex chromosome.
(2) ZZ male and ZW females (most birds and some insects)
The males are the ones who have two large sex chromosomes and the female has one large and one small sex chromosomes ie the reverse of that of human beings.
(3) Diploid females and haploid males (honey bees and ants)
The fertilised eggs become females (queens and worker bees) and the un-fertilised becomes the drones or kings.
(4) Temperature during incubation of eggs controls sex of offspring(crocodiles, turtles and tortoises)
(5) Sex changes with the environment. The dominant fish may change from one sex to the other depending on the population requirements at the time. (clown fish and many other fish)
(6) Hermaphrodites (nematodes, snails, slugs and earthworms)
They are both male and female at the same time as they have both fully functional male and female sex organs.
(7) Parthenogenesis (many species of insects, especially aphids)
The females give rise to offspring without sex. the eggs develop into new babies without the need for fertilisation. This is also known as virgin birth. It has also been documented in lonely female sharks kept in labs from birth with no other sharks in sight for miles around.
You may want to click on the following link to read more on this topic. Sex determination systems
Please do understand that these are all normal sex determination systems in these particular organisms. Do not mix these up with sex aberrations which are actually mistakes in chromosome or chromosomal mutations.
Cheers
We will discuss the sex aberrations in man on another posting as you have requested many times in class.
Do you know that not all organisms are like humans having the XY sex determination system?Human males are XY and females are XX. (humans beings)
The female has two large sex chromosomes and the male has one large and one small sex chromosome.
The other systems are:
(1) XX female and XO males (grasshopper, cockroaches and crickets)
The females have two sex chromosome and the male has only one sex chromosome.
(2) ZZ male and ZW females (most birds and some insects)
The males are the ones who have two large sex chromosomes and the female has one large and one small sex chromosomes ie the reverse of that of human beings.
(3) Diploid females and haploid males (honey bees and ants)
The fertilised eggs become females (queens and worker bees) and the un-fertilised becomes the drones or kings.
(4) Temperature during incubation of eggs controls sex of offspring(crocodiles, turtles and tortoises)
(5) Sex changes with the environment. The dominant fish may change from one sex to the other depending on the population requirements at the time. (clown fish and many other fish)
(6) Hermaphrodites (nematodes, snails, slugs and earthworms)They are both male and female at the same time as they have both fully functional male and female sex organs.
(7) Parthenogenesis (many species of insects, especially aphids)
The females give rise to offspring without sex. the eggs develop into new babies without the need for fertilisation. This is also known as virgin birth. It has also been documented in lonely female sharks kept in labs from birth with no other sharks in sight for miles around.
You may want to click on the following link to read more on this topic. Sex determination systems
Please do understand that these are all normal sex determination systems in these particular organisms. Do not mix these up with sex aberrations which are actually mistakes in chromosome or chromosomal mutations.
Cheers
We will discuss the sex aberrations in man on another posting as you have requested many times in class.
Panda galore
Read more about the panda-monium at Wolong National Nature Reserve, in Sichuan Province, south west China
All hese 16 pandas were bred at the breeding centre in southern China. They are extremely rare even in China where they are endemic. They are also difficult to bred as they are very slow breeders who give birth to only one or at most 2 cubs per pregnancy. Their diet is also very restrictive, feeding only on bamboo leaves and shoots.
Cheers
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