I just received my results for my Term 3 Science Test, and the mark drove me up the wall. 29.5/40, that's half mark away from A1!!
For one of the MCQs, I was pondering whether bronze or limestone is a compound. I choose bronze, but ironically, I put bronze as a mixture in another question!! I was thinking to myself that limestone could not be a compound and either I would get this question incorrect, or the other one. Ah...
Now I realised, we use mercury as tooth fillings. I thought that mercury was a liquid at room temperature, so it could never be the material for fillings, so wrote iron as my answer...
These evil mistakes have ruined my possibility for an exemption, that leaves only Infocomm Studies, Art Elective Programme and Higher Chinese as the possibilities for exemption.
Ahh... I hate myself! Why couldn't I achieve 30.5, like I did in Term 1? Now, I must concentrate on the coming Language Arts, Mathematics and Higher Chinese paper. What's the past is the past. Look to the future.
ああ～嫌いですね！ソファバード！この分はよくありませんでした！ああ～
Friday, August 20, 2010
Sex-determination systems
I have recently researched on the various systems that determine the gender of an animal. Here are some of the systems:
XY : The XY system is used in all placental, marsupial and echidna monotrome mammals, fruit flies and gingkoes. Females would have two X chromosomes and are called the homogametic sex. Males would have one X and one Y chromosome, and are referred to as the heterogametic sex. In this system, it is the male's sperm that determines the gender of the offspring. This was first described independently by Nettie Stevens and Edmund Beecher Wilson in 1905.
Video on XY system: http://www.youtube.com/watch?v=r0byeqI0FRg
ZW : The ZW system is used in all species of birds, some fish, crustaceans, insects and reptiles. This system's name is created to differentiate it from the XY system. The females have one Z and one W chromosome and are called the heterogametic sex, while the males have two Z chromosome and are referred to as the homogametic sex, as opposed to the XY system. Here, it is the ovum that determines the offspring's sex. In birds, no ZWW set has been found, though it is possible for moths. Though XY and ZW systems have no genes in common, they originated from a same ancestor.
X0 : The X0 system is used in grasshoppers, crickets, cockroaches and several other insect species. The male would have one X chromosome while the female has two. Like the XY system, the sperm of the male determines the sex, but it may contain no chromosome at all. For the fruit flies in the XY system, if they lose a Y chromosome, they would have X0 chromosomes as well.
Haplodiploid : The haplodiploid system is used in bees, wasps, ants, bark bettles, rotifers and spider mites. In this system, the union of a sperm and egg forms a female, while an unfertilized egg develop into a male. In this case, males have half the number of chromosomes females have.
Temperature-dependent : This system relies on temperature to determine the sex, and is used in crocodilians, tortoises and tautaras. Lower temperatures produce females while higher temperatures produce males. However, the biggest downside to this system is, as today's climate gets highly unpredictable due to environmental issues and pushes temperatures to the extremes, the eggs produced might be only of one gender so the offspring cannot reproduce, thus will become extinct. This might be one of the possible reasons why dinosaurs, plesiosaurs and pterosaurs died out.
Sex Change : Some animals that would change their gender during their lifetime include:
- snails (start as male, then become female)
- clown fish (dominant one is female, others are all male)
- blue wrasse fish (dominant one is male, others are all female)
- potato bass (change sex whenever they want)
- marine worm (turns male when contacting with female, turns female when contacted with the sea floor)
- human beings (through surgical means for own's preference)
Animals with unusual/uncomprehendable systems:
- swordfish
- chironomous midge
- platypus
XY : The XY system is used in all placental, marsupial and echidna monotrome mammals, fruit flies and gingkoes. Females would have two X chromosomes and are called the homogametic sex. Males would have one X and one Y chromosome, and are referred to as the heterogametic sex. In this system, it is the male's sperm that determines the gender of the offspring. This was first described independently by Nettie Stevens and Edmund Beecher Wilson in 1905.
Video on XY system: http://www.youtube.com/watch?v=r0byeqI0FRg
ZW : The ZW system is used in all species of birds, some fish, crustaceans, insects and reptiles. This system's name is created to differentiate it from the XY system. The females have one Z and one W chromosome and are called the heterogametic sex, while the males have two Z chromosome and are referred to as the homogametic sex, as opposed to the XY system. Here, it is the ovum that determines the offspring's sex. In birds, no ZWW set has been found, though it is possible for moths. Though XY and ZW systems have no genes in common, they originated from a same ancestor.
X0 : The X0 system is used in grasshoppers, crickets, cockroaches and several other insect species. The male would have one X chromosome while the female has two. Like the XY system, the sperm of the male determines the sex, but it may contain no chromosome at all. For the fruit flies in the XY system, if they lose a Y chromosome, they would have X0 chromosomes as well.
Haplodiploid : The haplodiploid system is used in bees, wasps, ants, bark bettles, rotifers and spider mites. In this system, the union of a sperm and egg forms a female, while an unfertilized egg develop into a male. In this case, males have half the number of chromosomes females have.
Temperature-dependent : This system relies on temperature to determine the sex, and is used in crocodilians, tortoises and tautaras. Lower temperatures produce females while higher temperatures produce males. However, the biggest downside to this system is, as today's climate gets highly unpredictable due to environmental issues and pushes temperatures to the extremes, the eggs produced might be only of one gender so the offspring cannot reproduce, thus will become extinct. This might be one of the possible reasons why dinosaurs, plesiosaurs and pterosaurs died out.
Sex Change : Some animals that would change their gender during their lifetime include:
- snails (start as male, then become female)
- clown fish (dominant one is female, others are all male)
- blue wrasse fish (dominant one is male, others are all female)
- potato bass (change sex whenever they want)
- marine worm (turns male when contacting with female, turns female when contacted with the sea floor)
- human beings (through surgical means for own's preference)
Animals with unusual/uncomprehendable systems:
- swordfish
- chironomous midge
- platypus
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