Form6 Biology

原帖由 Momo熊 于 22-9-2005 08:45 PM 发表
根據Pelangi那本,
Absolute estimation
-use of direct measurements
-may be continuous/discontinuous
-based on arbitrary opinion

Relative estimation
-product of 2 absolute measurements estimat ...

谢谢你Momo熊。我想问根据MPM的marking scheme生物的essay一个point是不是半分？

Momo熊

不用客气。
这我就没听说过了耶。
学校老师改都是一分一个idea。

蝎杰

我老师是用半分一个point的方法。
有谁可以解释给我知道genetic drift是什么吗？？？
还有怎样用pedigree analysis来分辨疾病是由gene autosom dominant/reccesive呢？？

蝎杰

有谁可以解释formation of urine 吗？尤其是reabsorption里的loop of henle那一part.

回去看学校用的CD就行了。CD解释得很清楚。

QooLuo

前几天考试的时候碰到这个题目：
A strain of the African Clawed Toad, Xenopus laevis exists in which there is only one nucleolus in the nucleus of each cell instead of the usual two.
When such animal are mated, approximately one quarter of the offspring have two nucleoli per nucleus, one half have one nucleolus per nucleus and one quarter have no nucleoli at all. Offspring without nucleoli die about four days after hatching.
These offspring die because they
A. do not have DNA that control the activities of cells.
B. have abnormal mitochondria that cannot generate energy effectively.
C. do not have ribosomes and are unable to manufacture protein.
D. do not have yolk and are unable to feed.

答案是C。 但为什么是C？

asapolh

如果他放 unable to manufacture protein 我还可能会选它，但为什么和 ribosome 有关呢？
我也想知道。。。

katsudon

知不知道nucleolus的功能是produces ribosomes？
没有nucleolus就没有ribosomes也就不能manufacture protein了。

QooLuo

原来如此。。谢谢katsudon的解答。。

请问你们有雨天之魂坛主的生物笔记吗？有的话麻烦你们寄给我。我的e-mail是[email protected]。谢谢

蝎杰

原帖由 lmenwe 于 4-10-2005 03:39 PM 发表
回去看学校用的CD就行了。CD解释得很清楚。

抱歉，我校应该不会借学生的。
你知道吗？可以解释给我听吗？

蝎杰

有些问题，不会做，不知道有谁为我解答呢？
在此先谢谢了！！

the flower of garden pea plants may be either white or purple.it is determined by 2 pairs of alleles(R,r,and S,s).if at least 1 dominat allele from each allelic pair is present,then the colour is purple.if a purpleplant with a genotype RrSs had 2 pure-breeding white parental plants,the genotypes of these plants would be。。。
A RRss and rrss
B RRss and RRss
C rrSS and rrss
D rrSS and RRss

in maize plant,the allele which codes for the synthesis of strach (S) is dominant to the allele (s) which cannot code for its synthesis.if 2 heterozygous (Ss) maize plant are crossed,what would be the possible genotypes of the resulting endosperm tissue?
A 1/4 SSs   1/2 Sss  1/4 sss
B 1/4 SSS   1/2 Sss  1/4 sss
C 1/4 SSS   1/2 SSs  1/4 Sss
D 1/4 SSS   1/4 SSs  1/4 Sss  1/4 sss

a couple who are both normal for blood clotting have 2 sons.what is the probability that both of them will be haemphiliacs?

a man shows normal blood clotting and is a non-taster for the chemical(PTC).his wife also shows normal blood cloting but is a taster.she is heterozygous for both the traits.what is the probability that their first child will be a son being a haemophliac and non-taster?

wispyjas

the flower of garden pea plants may be either white or purple.it is determined by 2 pairs of alleles(R,r,and S,s).if at least 1 dominat allele from each allelic pair is present,then the colour is purple.if a purpleplant with a genotype RrSs had 2 pure-breeding white parental plants,the genotypes of these plants would be。。。
A RRss and rrss
B RRss and RRss
C rrSS and rrss
D rrSS and RRss

答案應該是：D

“at least 1 dominat allele from each allelic pair is present,then the colour is purple.”

這句話的意思是在兩雙alleles有 R ＋ S的話，花的顏色就是紫色，這等於 RRSs，RrSS，RrSs 都是紫色。

rrss，RRss，rrSs，Rrss 和 rrSS 都是白色。

因為兩個父母都是白色rrSS and RRss符合這個條件，加上只有這個組合才能夠配出genotype RrSs

wispyjas

in maize plant,the allele which codes for the synthesis of strach (S) is dominant to the allele (s) which cannot code for its synthesis.if 2 heterozygous (Ss) maize plant are crossed,what would be the possible genotypes of the resulting endosperm tissue?
A 1/4 SSs   1/2 Sss  1/4 sss
B 1/4 SSS   1/2 Sss  1/4 sss
C 1/4 SSS   1/2 SSs  1/4 Sss
D 1/4 SSS   1/4 SSs  1/4 Sss  1/4 sss

答案應該是：D

之前，你要瞭解什麼是endosperm tissue。endosperm tissue是2個POLAR NUCLEI 加 MALE NUCLEUS 形成的 TRIPLOID TISSUE。

POLAR NUCLEI 可以是 SS 或者是 ss，不可以是 Ss （參考OVARY DEVELOPMENT 的過程）
MALE NUCLEUS 可以是 S 或者是 s

所以組成的組合應該有四個。

wispyjas

抱歉！第三的問題我不明白問題的要求，所以幫不到你了。

蝎杰

谢谢wispyjas替我解答！
其实这些问题是选择题，只是我懒得打它的选择答案出来而已。
a couple who are both normal for blood clotting have 2 sons.what is the probability that both of them will be haemphiliacs?
A 1/16
B 1/8
C 1/4
D 1/2

a man shows normal blood clotting and is a non-taster for the chemical(PTC).his wife also shows normal blood cloting but is a taster.she is heterozygous for both the traits.what is the probability that their first child will be a son being a haemophliac and non-taster?
A 0.0625
B 0.125
C 0.5
D 0.75

然后还有这些，我不懂....
the incidence of recessive albinism is 0.0004 in a human population .what is the frequency of the homozygous dominant individuals?

in a population where 7% of the babies are born with sickle-cell anaemia ,what is the heterozygous genotype?

asapolh

怪不得觉得这些问题很熟，是 longman 的吧？
先回答你前两个问题。。。
a couple who are both normal for blood clotting have 2 sons.what is the probability that both of them will be haemphiliacs?
A 1/16
B 1/8
C 1/4
D 1/2
答案是 A， 妈妈是 carier, 也就是 heterozygous for blood cotting. 他们的孩子有0.5机会是男的，男的有0.5机会是haemophiliac，所以是0.5 x 0.5 = 0.25
现在要both of the son is haemophiliac， 就 0.25 x 0.25 = 0.125 ＝ １／１６

a man shows normal blood clotting and is a non-taster for the chemical(PTC).his wife also shows normal blood cloting but is a taster.she is heterozygous for both the traits.what is the probability that their first child will be a son being a haemophliac and non-taster?
A 0.0625
B 0.125
C 0.5
D 0.75
答案是 B
这问题 involve sex-linked n somatic gene（忘了叫什么，我先这样称呼）
这里说到father是normal blood clotting and is a non-taster for the chemical(PTC)，所以他会是hemizygous 还有 homozygous for PTC taster. Mother 则是 heterozygous for both.....
Father:XHY　 tt
Mother:XHXh　Tt
(t = allele for non taster, T = allele for taster)
他们有儿子的 probability 是 0.5
孩子是 taster 的 probability 是 0.5
孩子是 haemophiliac 的 probability 是 0.5
所以是 0.5 x 0.5 x 0.5 ＝ 0.125

asapolh

the incidence of recessive albinism is 0.0004 in a human population .what is the frequency of the homozygous dominant individuals?
p: freq. for dominant allele
q: freq. for recessive allele
qq = freq. for homozygous recessive = 0.0004
q = 0.02
p = 1-0.02 = 0.98
pp = freq. for homozygous domonant = 0.98 x 0.98
   = 0.96


in a population where 7% of the babies are born with sickle-cell anaemia ,what is the heterozygous genotype?
这答案有问题，它给的答案是 for homozygous dominant 的。。。

蝎杰

谢谢asapolh替我解答！

想问SPECIATION的问题。
造成SPECIATION的原因isolation,genetic drift,hybridisation,和adaptive radiation。
而isolation又分为extrinsic&intrinsic isolation对吗？但我不明白的就是intrinsic isolation它是prevent formation of hybrid zygote哪又何来有SPECIATION呢？
而genectic drift的原理我不是很懂，有谁可以清楚地解释给我听吗？（尤其是founder effect的）
bottleneck effect 为何会lost of genectic variantion呢？
如果它是没有variantion1的话，那么有怎么能进行speciation呢？

雨天之魂

现在的情况不容许我回复太多。

针对你genectic drift的部分， 指的是随机而造成的改变。
给你一个例子， 同样数量的白色虫虫和黑色虫虫在一片叶子上。
一阵风刮来， 很多白色的虫虫被吹走了。
白色虫虫在这个 population 里占的比例相对就少了。
造成这个情形的原因纯粹是随机 (random， change by chance).
不是任何一方有特别的优势。

founder effect  指在一个地区， 特定的一个属性被大量的遗传下来， 而事实上该属性并没有什么特别的优势， 纯粹是运气而已。

bottleneck effect is serious in small population， and may lead to lose of genetic variation.
当一个地区的 population 小， 变动就会占很大的比例。如果总共有一万只虫， 风吹走了一只白色的， 变动的比例是万分之一。 如果只有十只， 变动的就是十分一了。

比如说， 再一阵大风来， 所有的白虫都被消灭了。 白色的品种就不见了。