Read the text and answer the questions




Do you look more like your father or grandfather? Do you have yourfather'seyes? What about Uncle Adam's cheekbones? Brown eyes, blue, green, or gray; black, brown, blond, or red hair-these are just a few examples of the traits that are inherited from parents. What genetic principles account for the transmission of such traits from parent to offspring? The answer is the gene.


What is genetics?


Genetics is the study of genes. In other words, it is the branch of biology that deals with the study of heredity. A gene is a segment of DMA that codes a partic­ular trait. It is the basic unit of hereditary. Genes are located on chromosomes. They control an organism's body form and function. The different forms of a trait that a gene may have are called alleles. Some alleles can be dominant and others can be recessive. If you get a dominant gene from either of your parents, you will look more like the one from whom you received that gene.



The molecular basis of inheritance


Why was the alphabet one of the first things you learned when you started school? Letters are a code that you need to know before you learn to read.

A cell also uses a code that is stored in its hereditary material. The code is a chemical called deoxyribonucleic acid, or DNA. It contains infor­mation for an organism's growth and function.

DNA is stored in cells that have a nucleus. When a cell divides, the DNA code is copied and passed to the new cells.

In this way, new cells receive the same coded information that was in the original cell. Every cell that has ever been formed in your body or in any other organism contains DNA

Genome sizes

Organism Genome size Estimated gene number
Human 3200 Mb 30.000-40.000
Fruit fly 180 Mb 13000
Yeast 12 Mb 6000
Bacteria 1.8 Mb 1700

1 Mb = million base




Genes in action (Protein synthesis)

Most of your characteristics, such as the color of your hair, your height, and even how things taste to you, depend on the kinds of proteins your cells make. DNA in your cells stores the instructions for making these proteins. Proteins build cells and tissues or work as enzymes. The instructions for making a spe­cific protein are found in a gene, which is a section of DNA on a chromosome.

Each chromosome contains hundreds of genes. Proteins are made of chains of hundreds or thousands of amino acids. The gene determines the order of amino acids in a protein. Changing the order of the amino acids makes a different pro­tein

What might occur if an important protein couldn't be made or if the wrong protein was made in your cells? Genes are found in the nucleus, but proteins are made on ribosomes in the cyto­plasm. The codes for making proteins are carried from the nucleus to the ribosomes by another type of nucleic acid called ribonucleic acid, or RNA.






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