[生物] Genetic 問題

我諗你或者將Allele 同 DNA 既 nitrogen bases 混淆左

首先, 我地要先攪清楚Allele, Gene 同 Chromosomes 既定義:

Chromosomes = 扭埋一團既 DNA
Gene = DNA 既一部分
Allele = 唔同版本既 Gene

換而言之, 其實 Gene 係大過 Chromosomes. 而當我地比較兩個相同大少形狀既 Chromosomes (Homologous Chromosomes), o係一個位置有唔同既 Gene 既時候, 我地就會分果兩個唔同既 Gene 做兩個 Alleles.

Meiosis 分裂出黎既 Gamete 有 23 粒[唔同既] Chromosomes
因為佢地冇一樣大少同形狀既Chromosome 去比較, 所以雖然佢地有好多好多個Gene, 侮一個Gene 只係一個 "Allele".

2007-05-02 00:41:37 補充：
Allele = Gene < Chromosomes加油!!

我想問 DNA 係咪由 Allele -> Gene -> Chromosomes 組成?
No, the DNA is formed by three chemicals (1)organic bases: Adenine,(A), Thymine, (T), Cytosine ,(C) and Guanine ,(G). Organic bases bind to (2) pentose, a kind of 5-Carbon sugar to give nucleoside which will finally form phosphoester linkage with (3)phosphoric acid to give nucleotides. When nucleotides link together and pair up, a DNA is formed.
allele在gene裏面,而gene又在DNA裏面,一條highly coiled的DNA在metaphase (one of the steps of cell division)中形成chromosomes. The correct sequence should be: Allele -> Gene -> DNA->Chromosomes

(2 sets of alleles = 1 gene?) NO, see below.

每個 Gamete 係咪得一個 Allele? Of course NOT. In human, the male gamete is sperm containing all genetic information such as blood group, skin color, tall or short and any genetically related diseases' genes, coming from the foetus's father. At the same time, the female gamete is egg cell containing all genetic information coming from the foetus's mother. When they fuse together inside the fallopian tube, mitosis occurs and the genetic information will pass to the next generation during embryo formation. This means that a gamete contains a lot of alleles controlling different types of functions and traits.
即係得一個英文字母? Of course NOT. As blood groups, there are 4 types if they are classified at your level. They are A, B, AB and O. In genotype forms written as IAIA ,IAi(A形血), IBIB , IBi(B形血), IAIB(AB形血) and ii(O形血). They are called multiple allele. This means that in one gene there should be different alleles controlling the blood groups. 就算不是血形,而是豆的外形, 在一條gene裏面,也可以有平滑(smooth,用R表示dominant)及皺紋(用r表示recessive)之分別. 也即是說在一條gene裏面可以有多於一種的allele存在.

如果係既話, 起 Meiosis 果陣分裂出黎既 Gamete 有 23 Chromosomes,
咁點解得一個 Allele?
First, you concept is not so true. As you know, in our body, there are twenty three chromosomes. However, each chromosome is made up of high coiled DNA. Then the question is what is a gene? A gene is a segment of DNA molecules(是DNA的一節) which control our body's function. As the above mentioned, a gene may contain more than one allele and a gamete has different types of genes. This means that a gamete doesn't contain one allele only and this testifies your concept is not so right.
I hope you may find my writing helpful.

""我想問 DNA 係咪由 Allele -> Gene -> Chromosomes 組成?
(2 sets of alleles = 1 gene?)""

There is sth wrong in your concept.

First, DNA(DeoxyriboNucleic Acid) is an acidic molecule, DNA carries genetic info that determines the sequence of amino acids in proteins and regulates protein synthesis. It also determines the body characteristics of organisms and the metabolic activities of cells.

Second, Chromosome is made up of a lot of DNA molecules, they are found in nucleus.

Third, Gene(基因) is a small section of chromosome, which are basic units of inheritance. Each inherited characteristic is controlled by a gene or several genes.

Fourth, for each characteristic, there may be more than one type, eg blood type, there is blood type A, B, O, AB. This implies that there is more than one gene(at least a separate gene for each blood type). These alternative forms of genes representing characteristic of the same kind are called alleles(等位基因). Note that they could be found at the same place of homologous chromosome(同源染色體).

Thus considering the size, we have chromosome > gene, allele > DNA molecule

""每個 Gamete 係咪得一個 Allele? 即係得一個英文字母?
如果係既話, 起 Meiosis 果陣分裂出黎既 Gamete 有 23 Chromosomes,
咁點解得一個 Allele?""

As your previous concepts are wrong, this is then also wrong.

When we consider inheritance, we usually consider each different characteristic separately. In CE level(I think you are at CE level), characterisitc controlled by one gene is studied only. Maybe this time we consider tongue rolling(a characterisitc controlled by one gene), the relevant gene in the gametes is then shown graphically. But it doesn't mean that each gamete contains only one gene.

For human gametes, each contains 23 chromosomes, each chromosomes can be divided into a lot of sections, thus there is more than 23 genes, actually thousands of genes.

Additional info: Steps of mitosis and meiosis

step of mitotic cell division
1)chromosomes replicate
2)chromosomes appear visible like "X", ie w/2 chromatids
3)nuclear membrane disintegrates
4)chromosomes line up at equator
5)spindle fibre pull chromatids towards the poles
6)formation of nuclear membrane around 2set of chromosomes
7)chromosomes appear invisible
8)cell membrane constricts and cytoplasm is divided(animal cells)
formation of new cell walls and cell membranes between nuclei(plant cells)

step of meiotic cell division
1)chromosomes replicate
2)chromosomes shorten and thicken and appear visible as small threads
3)homologous chromosomes pair up
4)nuclear membrane disintegrates, chromosomes appear w/2 chromatids
4)homologous chromosomes line up at equator in pairs
5)spindle fibre pull homologous chromosomes towards the poles(E-W direction)
ie homologous chromosomes members separate from each other
6)formation of nuclear membrane around 2 haploid set of chromosomes
7)nuclear membrane disintegrates
8)chromosomes line up at equator
9)spindle fibre pull chromatids towards the poles(N-S direction)
10)formation of nuclear membrane around 4 haploid set of chromosomes
11)chromosomes uncoil and appear invisible
12)cytoplasm divides and formation of new cell membranes