3.1DNA, Chromosome and Gene
DNA or acid is a huge and complex deoxyribonucleic molecule. It carries the genetic code that determines the characteristics of a living thing. It is located in the nucleus of a cell. Everyone has a unique set of DNA. except identical twins.
The DNA molecule is made up of long chains of nucleotides. Each nucleotide has three parts a nitrogenous base, a pentose(five-carbon sugar molecule and a phosphate group.
The nucleotides join up by condensation reactions to form a long polynucleotide. The backbone of this long chain is a chain of sugar and phosphate molecules.
There are four types of nitrogenous bases in the polynucleotide - adenine(A), thymine(T), (C) and guanine(G). A DNA molecule actually consists of two polynucleotide chains that twisted around each other to form a double helix.
The two polynucleotide chains are linked together by hydrogen bonds between the bases. Cytosine(C) always pairs with guanine(G), and adenine(A) always pairs with thymine(T).
The DNA molecule has two important features. It can make copy of itself during cell division and it can carry information.
Gene
A gene is a section of DNA. Genes are coded instructions to make everything the body needs, specially proteins.
Chromosome
In the nucleus, the DNA is tightly packed into structures known as chromosomes. Figure 3.6 shows the relationship between chromosome and gene.
The number of chromosomes in each species is constant. As the chromosomes in the nuclei are always in pair, the chromosome number is said to be diploid and is represented by the symbol 2n. Different species have different chromosome numbers.
Species
- Homo sapiens (human)
- Zea mays (corn)
- Gallus domesticus (chicken)
- Sacchoromyces cerevisiae (yeast)
- Drosophila melanogaster (fruit fly)
In our body cells, there are 23 pairs of chromosomes and about 20 000 to 25 000 genes located on them. Each pair of the chromosomes is called a pair of homologous chromosomes. Homologous chromosomes are similar in shape and size, and carry the same types of genes.
3.1DNA, Chromosome and Gene DNA or acid is a huge and complex deoxyribonucleic molecule. It carries the genetic code that determines the characteristics of a living thing. It is located in the nucleus of a cell. Everyone has a unique set of DNA. except identical twins. The DNA molecule is made up of long chains of nucleotides. Each nucleotide has three parts a nitrogenous base, a pentose(five-carbon sugar molecule and a phosphate group. The nucleotides join up by condensation reactions to form a long polynucleotide. The backbone of this long chain is a chain of sugar and phosphate molecules.There are four types of nitrogenous bases in the polynucleotide - adenine(A), thymine(T), (C) and guanine(G). A DNA molecule actually consists of two polynucleotide chains that twisted around each other to form a double helix.The two polynucleotide chains are linked together by hydrogen bonds between the bases. Cytosine(C) always pairs with guanine(G), and adenine(A) always pairs with thymine(T). The DNA molecule has two important features. It can make copy of itself during cell division and it can carry information.Gene A gene is a section of DNA. Genes are coded instructions to make everything the body needs, specially proteins.ChromosomeIn the nucleus, the DNA is tightly packed into structures known as chromosomes. Figure 3.6 shows the relationship between chromosome and gene.จำนวน chromosomes ในแต่ละชนิดจะคง เป็น chromosomes ในแอลฟาเสมอในคู่ จำนวนโครโมโซมกล่าวได้ว่า เป็น diploid และถูกแทน ด้วย 2n สัญลักษณ์ สายพันธุ์ต่าง ๆ มีจำนวนโครโมโซมแตกต่างกันสปีชีส์ -กะเทย sapiens (มนุษย์)-ซี mays (ข้าวโพด) -Gallus domesticus (ไก่) -Sacchoromyces cerevisiae (ยีสต์) -แมลงวันทอง (แมลงวันผลไม้)ในเซลล์ร่างกายของเรา มี 23 คู่ของ chromosomes และยีนเกี่ยวกับ 20 000 กับ 25 000 อยู่นั้น แต่ละคู่ของ chromosomes เรียกว่าคู่ของ homologous chromosomes Homologous chromosomes คล้ายในรูปร่างและขนาด และมียีนเหมือนกัน
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